#
This Clause describes components that C++ programs may use to perform input/output operations.
2
#
The following subclauses describe requirements for stream parameters, and components for forward declarations of iostreams, predefined iostreams objects, base iostreams classes, stream buffering, stream formatting and manipulators, string streams, and file streams, as summarized in Table 135.
Table 135 — Input/output library summary [tab:iostreams.summary]
🔗
Subclause
Header
🔗
Requirements
🔗
Forward declarations
<iosfwd>
🔗
Standard iostream objects
<iostream>
🔗
Iostreams base classes
<ios>
🔗
Stream buffers
<streambuf>
🔗
Formatting and manipulators
<istream>, <ostream>, <iomanip>, <print>
🔗
String streams
<sstream>
🔗
Span-based streams
<spanstream>
🔗
File streams
<fstream>
🔗
Synchronized output streams
<syncstream>
🔗
File systems
<filesystem>
🔗
C library files
<cstdio>, <cinttypes>

31.2 Iostreams requirements [iostreams.requirements]

31.2.1 Imbue limitations [iostream.limits.imbue]

1
#
No function described in [input.output] except for ios_base​::​imbue and basic_filebuf​::​pubimbue causes any instance of basic_ios​::​imbue or basic_streambuf​::​imbue to be called.
If any user function called from a function declared in [input.output] or as an overriding virtual function of any class declared in [input.output] calls imbue, the behavior is undefined.
🔗
using streamoff = implementation-defined;
1
#
The type streamoff is a synonym for one of the signed basic integral types of sufficient size to represent the maximum possible file size for the operating system.247
🔗
using streamsize = implementation-defined;
2
#
The type streamsize is a synonym for one of the signed basic integral types.
It is used to represent the number of characters transferred in an I/O operation, or the size of I/O buffers.248
247)247)
Typically long long.
248)248)
Most places where streamsize is used would use size_t in C, or ssize_t in POSIX.

31.2.3 Positioning type limitations [iostreams.limits.pos]

1
#
The classes of [input.output] with template arguments charT and traits behave as described if traits​::​pos_type and traits​::​off_type are streampos and streamoff respectively.
Except as noted explicitly below, their behavior when traits​::​pos_type and traits​::​off_type are other types is implementation-defined.
2
#
[Note 1: 
For each of the specializations of char_traits defined in [char.traits.specializations], state_type denotes mbstate_t, pos_type denotes fpos<mbstate_t>, and off_type denotes streamoff.
— end note]
3
#
In the classes of [input.output], a template parameter with name charT represents a member of the set of types containing char, wchar_t, and any other implementation-defined character container types ([defns.character.container]) that meet the requirements for a character on which any of the iostream components can be instantiated.
1
#
Concurrent access to a stream object ([string.streams], [file.streams]), stream buffer object ([stream.buffers]), or C Library stream ([c.files]) by multiple threads may result in a data race ([intro.multithread]) unless otherwise specified ([iostream.objects]).
[Note 1: 
Data races result in undefined behavior ([intro.multithread]).
— end note]
2
#
If one thread makes a library call a that writes a value to a stream and, as a result, another thread reads this value from the stream through a library call b such that this does not result in a data race, then a's write synchronizes with b's read.

31.3 Forward declarations [iostream.forward]

31.3.1 Header <iosfwd> synopsis [iosfwd.syn]

🔗
namespace std { template<class charT> struct char_traits; template<> struct char_traits<char>; template<> struct char_traits<char8_t>; template<> struct char_traits<char16_t>; template<> struct char_traits<char32_t>; template<> struct char_traits<wchar_t>; template<class T> class allocator; template<class charT, class traits = char_traits<charT>> class basic_ios; template<class charT, class traits = char_traits<charT>> class basic_streambuf; template<class charT, class traits = char_traits<charT>> class basic_istream; template<class charT, class traits = char_traits<charT>> class basic_ostream; template<class charT, class traits = char_traits<charT>> class basic_iostream; template<class charT, class traits = char_traits<charT>, class Allocator = allocator<charT>> class basic_stringbuf; template<class charT, class traits = char_traits<charT>, class Allocator = allocator<charT>> class basic_istringstream; template<class charT, class traits = char_traits<charT>, class Allocator = allocator<charT>> class basic_ostringstream; template<class charT, class traits = char_traits<charT>, class Allocator = allocator<charT>> class basic_stringstream; template<class charT, class traits = char_traits<charT>> class basic_spanbuf; template<class charT, class traits = char_traits<charT>> class basic_ispanstream; template<class charT, class traits = char_traits<charT>> class basic_ospanstream; template<class charT, class traits = char_traits<charT>> class basic_spanstream; template<class charT, class traits = char_traits<charT>> class basic_filebuf; template<class charT, class traits = char_traits<charT>> class basic_ifstream; template<class charT, class traits = char_traits<charT>> class basic_ofstream; template<class charT, class traits = char_traits<charT>> class basic_fstream; template<class charT, class traits = char_traits<charT>, class Allocator = allocator<charT>> class basic_syncbuf; template<class charT, class traits = char_traits<charT>, class Allocator = allocator<charT>> class basic_osyncstream; template<class charT, class traits = char_traits<charT>> class istreambuf_iterator; template<class charT, class traits = char_traits<charT>> class ostreambuf_iterator; using ios = basic_ios<char>; using wios = basic_ios<wchar_t>; using streambuf = basic_streambuf<char>; using istream = basic_istream<char>; using ostream = basic_ostream<char>; using iostream = basic_iostream<char>; using stringbuf = basic_stringbuf<char>; using istringstream = basic_istringstream<char>; using ostringstream = basic_ostringstream<char>; using stringstream = basic_stringstream<char>; using spanbuf = basic_spanbuf<char>; using ispanstream = basic_ispanstream<char>; using ospanstream = basic_ospanstream<char>; using spanstream = basic_spanstream<char>; using filebuf = basic_filebuf<char>; using ifstream = basic_ifstream<char>; using ofstream = basic_ofstream<char>; using fstream = basic_fstream<char>; using syncbuf = basic_syncbuf<char>; using osyncstream = basic_osyncstream<char>; using wstreambuf = basic_streambuf<wchar_t>; using wistream = basic_istream<wchar_t>; using wostream = basic_ostream<wchar_t>; using wiostream = basic_iostream<wchar_t>; using wstringbuf = basic_stringbuf<wchar_t>; using wistringstream = basic_istringstream<wchar_t>; using wostringstream = basic_ostringstream<wchar_t>; using wstringstream = basic_stringstream<wchar_t>; using wspanbuf = basic_spanbuf<wchar_t>; using wispanstream = basic_ispanstream<wchar_t>; using wospanstream = basic_ospanstream<wchar_t>; using wspanstream = basic_spanstream<wchar_t>; using wfilebuf = basic_filebuf<wchar_t>; using wifstream = basic_ifstream<wchar_t>; using wofstream = basic_ofstream<wchar_t>; using wfstream = basic_fstream<wchar_t>; using wsyncbuf = basic_syncbuf<wchar_t>; using wosyncstream = basic_osyncstream<wchar_t>; template<class state> class fpos; using streampos = fpos<char_traits<char>::state_type>; using wstreampos = fpos<char_traits<wchar_t>::state_type>; using u8streampos = fpos<char_traits<char8_t>::state_type>; using u16streampos = fpos<char_traits<char16_t>::state_type>; using u32streampos = fpos<char_traits<char32_t>::state_type>; }
1
#
Default template arguments are described as appearing both in <iosfwd> and in the synopsis of other headers but it is well-formed to include both <iosfwd> and one or more of the other headers.249
249)249)
It is the implementation's responsibility to implement headers so that including <iosfwd> and other headers does not violate the rules about multiple occurrences of default arguments.
1
#
The class template specialization basic_ios<charT, traits> serves as a virtual base class for the class templates basic_istream, basic_ostream, and class templates derived from them.
basic_iostream is a class template derived from both basic_istream<charT, traits> and basic_ostream<charT, traits>.
2
#
The class template specialization basic_streambuf<charT, traits> serves as a base class for class templates basic_stringbuf, basic_filebuf, and basic_syncbuf.
3
#
The class template specialization basic_istream<charT, traits> serves as a base class for class templates basic_istringstream and basic_ifstream.
4
#
The class template specialization basic_ostream<charT, traits> serves as a base class for class templates basic_ostringstream, basic_ofstream, and basic_osyncstream.
5
#
The class template specialization basic_iostream<charT, traits> serves as a base class for class templates basic_stringstream and basic_fstream.
6
#
[Note 1: 
For each of the class templates above, the program is ill-formed if traits​::​char_type is not the same type as charT ([char.traits]).
— end note]
7
#
Other typedef-names define instances of class templates specialized for char or wchar_t types.
8
#
Specializations of the class template fpos are used for specifying file position information.
[Example 1: 
The types streampos and wstreampos are used for positioning streams specialized on char and wchar_t respectively.
— end example]
9
#
[Note 2: 
This synopsis suggests a circularity between streampos and char_traits<char>.
An implementation can avoid this circularity by substituting equivalent types.
— end note]

31.4 Standard iostream objects [iostream.objects]

31.4.1 Header <iostream> synopsis [iostream.syn]

🔗
#include <ios> / see [ios.syn] #include <streambuf> / see [streambuf.syn] #include <istream> / see [istream.syn] #include <ostream> / see [ostream.syn] namespace std { extern istream cin; extern ostream cout; extern ostream cerr; extern ostream clog; extern wistream wcin; extern wostream wcout; extern wostream wcerr; extern wostream wclog; }
1
#
In this Clause, the type name FILE refers to the type FILE declared in <cstdio>.
2
#
The header <iostream> declares objects that associate objects with the standard C streams provided for by the functions declared in <cstdio>, and includes all the headers necessary to use these objects.
The dynamic types of the stream buffers initially associated with these objects are unspecified, but they have the behavior specified for std​::​basic_filebuf<char> or std​::​basic_filebuf<wchar_t>.
3
#
The objects are constructed and the associations are established at some time prior to or during the first time an object of class ios_base​::​Init is constructed, and in any case before the body of main ([basic.start.main]) begins execution.
The objects are not destroyed during program execution.250
4
#
Recommended practice: If it is possible for them to do so, implementations should initialize the objects earlier than required.
5
#
The results of including <iostream> in a translation unit shall be as if <iostream> defined an instance of ios_base​::​Init with static storage duration.
Each C++ library module ([std.modules]) in a hosted implementation shall behave as if it contains an interface unit that defines an unexported ios_base​::​Init variable with ordered initialization ([basic.start.dynamic]).
[Note 1: 
As a result, the definition of that variable is appearance-ordered before any declaration following the point of importation of a C++ library module.
Whether such a definition exists is unobservable by a program that does not reference any of the standard iostream objects.
— end note]
6
#
Mixing operations on corresponding wide- and narrow-character streams follows the same semantics as mixing such operations on FILEs, as specified in the C standard library.
7
#
Concurrent access to a synchronized ([ios.members.static]) standard iostream object's formatted and unformatted input ([istream]) and output ([ostream]) functions or a standard C stream by multiple threads does not result in a data race ([intro.multithread]).
[Note 2: 
Unsynchronized concurrent use of these objects and streams by multiple threads can result in interleaved characters.
— end note]
See also: ISO/IEC 9899:2024, 7.23.2
250)250)
Constructors and destructors for objects with static storage duration can access these objects to read input from stdin or write output to stdout or stderr.

31.4.3 Narrow stream objects [narrow.stream.objects]

🔗
istream cin;
1
#
The object cin controls input from a stream buffer associated with the object stdin, declared in <cstdio>.
2
#
After the object cin is initialized, cin.tie() returns &cout.
Its state is otherwise the same as required for basic_ios<char>​::​init.
🔗
ostream cout;
3
#
The object cout controls output to a stream buffer associated with the object stdout, declared in <cstdio>.
🔗
ostream cerr;
4
#
The object cerr controls output to a stream buffer associated with the object stderr, declared in <cstdio>.
5
#
After the object cerr is initialized, cerr.flags() & unitbuf is nonzero and cerr.tie() returns &cout.
Its state is otherwise the same as required for basic_ios<char>​::​init.
🔗
ostream clog;
6
#
The object clog controls output to a stream buffer associated with the object stderr, declared in <cstdio>.

31.4.4 Wide stream objects [wide.stream.objects]

🔗
wistream wcin;
1
#
The object wcin controls input from a stream buffer associated with the object stdin, declared in <cstdio>.
2
#
After the object wcin is initialized, wcin.tie() returns &wcout.
Its state is otherwise the same as required for basic_ios<wchar_t>​::​init.
🔗
wostream wcout;
3
#
The object wcout controls output to a stream buffer associated with the object stdout, declared in <cstdio>.
🔗
wostream wcerr;
4
#
The object wcerr controls output to a stream buffer associated with the object stderr, declared in <cstdio>.
5
#
After the object wcerr is initialized, wcerr.flags() & unitbuf is nonzero and wcerr.tie() returns &wcout.
Its state is otherwise the same as required for basic_ios<wchar_t>​::​init.
🔗
wostream wclog;
6
#
The object wclog controls output to a stream buffer associated with the object stderr, declared in <cstdio>.

31.5 Iostreams base classes [iostreams.base]

31.5.1 Header <ios> synopsis [ios.syn]

🔗
#include <iosfwd> / see [iosfwd.syn] namespace std { / [stream.types], types using streamoff = implementation-defined; using streamsize = implementation-defined; / [fpos], class template fpos template<class stateT> class fpos; / [ios.base], class ios_base class ios_base; / [ios], class template basic_ios template<class charT, class traits = char_traits<charT>> class basic_ios; / [std.ios.manip], manipulators ios_base& boolalpha (ios_base& str); ios_base& noboolalpha(ios_base& str); ios_base& showbase (ios_base& str); ios_base& noshowbase (ios_base& str); ios_base& showpoint (ios_base& str); ios_base& noshowpoint(ios_base& str); ios_base& showpos (ios_base& str); ios_base& noshowpos (ios_base& str); ios_base& skipws (ios_base& str); ios_base& noskipws (ios_base& str); ios_base& uppercase (ios_base& str); ios_base& nouppercase(ios_base& str); ios_base& unitbuf (ios_base& str); ios_base& nounitbuf (ios_base& str); / [adjustfield.manip], adjustfield ios_base& internal (ios_base& str); ios_base& left (ios_base& str); ios_base& right (ios_base& str); / [basefield.manip], basefield ios_base& dec (ios_base& str); ios_base& hex (ios_base& str); ios_base& oct (ios_base& str); / [floatfield.manip], floatfield ios_base& fixed (ios_base& str); ios_base& scientific (ios_base& str); ios_base& hexfloat (ios_base& str); ios_base& defaultfloat(ios_base& str); / [error.reporting], error reporting enum class io_errc { stream = 1 }; template<> struct is_error_code_enum<io_errc> : public true_type { }; error_code make_error_code(io_errc e) noexcept; error_condition make_error_condition(io_errc e) noexcept; const error_category& iostream_category() noexcept; }

31.5.2 Class ios_base [ios.base]

🔗
namespace std { class ios_base { public: class failure; / see below / [ios.fmtflags], fmtflags using fmtflags = T1; static constexpr fmtflags boolalpha = unspecified; static constexpr fmtflags dec = unspecified; static constexpr fmtflags fixed = unspecified; static constexpr fmtflags hex = unspecified; static constexpr fmtflags internal = unspecified; static constexpr fmtflags left = unspecified; static constexpr fmtflags oct = unspecified; static constexpr fmtflags right = unspecified; static constexpr fmtflags scientific = unspecified; static constexpr fmtflags showbase = unspecified; static constexpr fmtflags showpoint = unspecified; static constexpr fmtflags showpos = unspecified; static constexpr fmtflags skipws = unspecified; static constexpr fmtflags unitbuf = unspecified; static constexpr fmtflags uppercase = unspecified; static constexpr fmtflags adjustfield = see below; static constexpr fmtflags basefield = see below; static constexpr fmtflags floatfield = see below; / [ios.iostate], iostate using iostate = T2; static constexpr iostate badbit = unspecified; static constexpr iostate eofbit = unspecified; static constexpr iostate failbit = unspecified; static constexpr iostate goodbit = see below; / [ios.openmode], openmode using openmode = T3; static constexpr openmode app = unspecified; static constexpr openmode ate = unspecified; static constexpr openmode binary = unspecified; static constexpr openmode in = unspecified; static constexpr openmode noreplace = unspecified; static constexpr openmode out = unspecified; static constexpr openmode trunc = unspecified; / [ios.seekdir], seekdir using seekdir = T4; static constexpr seekdir beg = unspecified; static constexpr seekdir cur = unspecified; static constexpr seekdir end = unspecified; class Init; / [fmtflags.state], fmtflags state fmtflags flags() const; fmtflags flags(fmtflags fmtfl); fmtflags setf(fmtflags fmtfl); fmtflags setf(fmtflags fmtfl, fmtflags mask); void unsetf(fmtflags mask); streamsize precision() const; streamsize precision(streamsize prec); streamsize width() const; streamsize width(streamsize wide); / [ios.base.locales], locales locale imbue(const locale& loc); locale getloc() const; / [ios.base.storage], storage static int xalloc(); long& iword(int idx); void*& pword(int idx); / destructor virtual ~ios_base(); / [ios.base.callback], callbacks enum event { erase_event, imbue_event, copyfmt_event }; using event_callback = void (*)(event, ios_base&, int idx); void register_callback(event_callback fn, int idx); ios_base(const ios_base&) = delete; ios_base& operator=(const ios_base&) = delete; static bool sync_with_stdio(bool sync = true); protected: ios_base(); private: static int index; / exposition only long* iarray; / exposition only void* parray; / exposition only }; }
1
#
ios_base defines several member types:
  • (1.1)
    a type failure, defined as either a class derived from system_error or a synonym for a class derived from system_error;
  • (1.2)
    a class Init;
  • (1.3)
    three bitmask types, fmtflags, iostate, and openmode;
  • (1.4)
    an enumerated type, seekdir.
2
#
It maintains several kinds of data:
  • (2.1)
    state information that reflects the integrity of the stream buffer;
  • (2.2)
    control information that influences how to interpret (format) input sequences and how to generate (format) output sequences;
  • (2.3)
    additional information that is stored by the program for its private use.
3
#
[Note 1: 
For the sake of exposition, the maintained data is presented here as:
  • (3.1)
    static int index, specifies the next available unique index for the integer or pointer arrays maintained for the private use of the program, initialized to an unspecified value;
  • (3.2)
    long* iarray, points to the first element of an arbitrary-length long array maintained for the private use of the program;
  • (3.3)
    void* parray, points to the first element of an arbitrary-length pointer array maintained for the private use of the program.
— end note]

31.5.2.2.1 Class ios_base​::​failure [ios.failure]

🔗
namespace std { class ios_base::failure : public system_error { public: explicit failure(const string& msg, const error_code& ec = io_errc::stream); explicit failure(const char* msg, const error_code& ec = io_errc::stream); }; }
1
#
An implementation is permitted to define ios_base​::​failure as a synonym for a class with equivalent functionality to class ios_base​::​failure shown in this subclause.
[Note 1: 
When ios_base​::​failure is a synonym for another type, that type needs to provide a nested type failure to emulate the injected-class-name.
— end note]
The class failure defines the base class for the types of all objects thrown as exceptions, by functions in the iostreams library, to report errors detected during stream buffer operations.
2
#
When throwing ios_base​::​failure exceptions, implementations should provide values of ec that identify the specific reason for the failure.
[Note 2: 
Errors arising from the operating system would typically be reported as system_category() errors with an error value of the error number reported by the operating system.
Errors arising from within the stream library would typically be reported as error_code(io_errc​::​stream, iostream_category().
— end note]
🔗
explicit failure(const string& msg, const error_code& ec = io_errc::stream);
3
#
Effects: Constructs the base class with msg and ec.
🔗
explicit failure(const char* msg, const error_code& ec = io_errc::stream);
4
#
Effects: Constructs the base class with msg and ec.

31.5.2.2.2 Type ios_base​::​fmtflags [ios.fmtflags]

🔗
using fmtflags = T1;
1
#
The type fmtflags is a bitmask type ([bitmask.types]).
Setting its elements has the effects indicated in Table 136.
Table 136 — fmtflags effects [tab:ios.fmtflags]
🔗
Element
Effect(s) if set
🔗
boolalpha
insert and extract bool type in alphabetic format
🔗
dec
converts integer input or generates integer output in decimal base
🔗
fixed
generate floating-point output in fixed-point notation
🔗
hex
converts integer input or generates integer output in hexadecimal base
🔗
internal
adds fill characters at a designated internal point in certain generated output, or identical to right if no such point is designated
🔗
left
adds fill characters on the right (final positions) of certain generated output
🔗
oct
converts integer input or generates integer output in octal base
🔗
right
adds fill characters on the left (initial positions) of certain generated output
🔗
scientific
generates floating-point output in scientific notation
🔗
showbase
generates a prefix indicating the numeric base of generated integer output
🔗
showpoint
generates a decimal-point character unconditionally in generated floating-point output
🔗
showpos
generates a + sign in non-negative generated numeric output
🔗
skipws
skips leading whitespace before certain input operations
🔗
unitbuf
flushes output after each output operation
🔗
uppercase
replaces certain lowercase letters with their uppercase equivalents in generated output
2
#
Type fmtflags also defines the constants indicated in Table 137.
Table 137 — fmtflags constants [tab:ios.fmtflags.const]
🔗
Constant
Allowable values
🔗
adjustfield
left | right | internal
🔗
basefield
dec | oct | hex
🔗
floatfield
scientific | fixed

31.5.2.2.3 Type ios_base​::​iostate [ios.iostate]

🔗
using iostate = T2;
1
#
The type iostate is a bitmask type ([bitmask.types]) that contains the elements indicated in Table 138.
Table 138 — iostate effects [tab:ios.iostate]
🔗
Element
Effect(s) if set
🔗
badbit
indicates a loss of integrity in an input or output sequence (such as an irrecoverable read error from a file);
🔗
eofbit
indicates that an input operation reached the end of an input sequence;
🔗
failbit
indicates that an input operation failed to read the expected characters, or that an output operation failed to generate the desired characters.
2
#
Type iostate also defines the constant:

31.5.2.2.4 Type ios_base​::​openmode [ios.openmode]

🔗
using openmode = T3;
1
#
The type openmode is a bitmask type ([bitmask.types]).
It contains the elements indicated in Table 139.
Table 139 — openmode effects [tab:ios.openmode]
🔗
Element
Effect(s) if set
🔗
app
seek to end before each write
🔗
ate
open and seek to end immediately after opening
🔗
binary
perform input and output in binary mode (as opposed to text mode)
🔗
in
open for input
🔗
noreplace
open in exclusive mode
🔗
out
open for output
🔗
trunc
truncate an existing stream when opening

31.5.2.2.5 Type ios_base​::​seekdir [ios.seekdir]

🔗
using seekdir = T4;
1
#
The type seekdir is an enumerated type ([enumerated.types]) that contains the elements indicated in Table 140.
Table 140 — seekdir effects [tab:ios.seekdir]
🔗
Element
Meaning
🔗
beg
request a seek (for subsequent input or output) relative to the beginning of the stream
🔗
cur
request a seek relative to the current position within the sequence
🔗
end
request a seek relative to the current end of the sequence

31.5.2.2.6 Class ios_base​::​Init [ios.init]

🔗
namespace std { class ios_base::Init { public: Init(); Init(const Init&) = default; ~Init(); Init& operator=(const Init&) = default; }; }
1
#
The class Init describes an object whose construction ensures the construction of the eight objects declared in <iostream> ([iostream.objects]) that associate file stream buffers with the standard C streams provided for by the functions declared in <cstdio>.
🔗
Init();
2
#
Effects: Constructs and initializes the objects cin, cout, cerr, clog, wcin, wcout, wcerr, and wclog if they have not already been constructed and initialized.
🔗
~Init();
3
#
Effects: If there are no other instances of the class still in existence, calls cout.flush(), cerr.flush(), clog.flush(), wcout.flush(), wcerr.flush(), wclog.flush().

31.5.2.3 State functions [fmtflags.state]

🔗
fmtflags flags() const;
1
#
Returns: The format control information for both input and output.
🔗
fmtflags flags(fmtflags fmtfl);
2
#
Returns: The previous value of flags().
🔗
fmtflags setf(fmtflags fmtfl);
4
#
Effects: Sets fmtfl in flags().
5
#
Returns: The previous value of flags().
🔗
fmtflags setf(fmtflags fmtfl, fmtflags mask);
6
#
Effects: Clears mask in flags(), sets fmtfl & mask in flags().
7
#
Returns: The previous value of flags().
🔗
void unsetf(fmtflags mask);
8
#
Effects: Clears mask in flags().
🔗
streamsize precision() const;
9
#
Returns: The precision to generate on certain output conversions.
🔗
streamsize precision(streamsize prec);
10
#
Returns: The previous value of precision().
🔗
streamsize width() const;
12
#
Returns: The minimum field width (number of characters) to generate on certain output conversions.
🔗
streamsize width(streamsize wide);
13
#
Returns: The previous value of width().
🔗
locale imbue(const locale& loc);
1
#
Effects: Calls each registered callback pair (fn, idx) ([ios.base.callback]) as (*fn)(imbue_event, *this, idx) at such a time that a call to ios_base​::​getloc() from within fn returns the new locale value loc.
2
#
Returns: The previous value of getloc().
🔗
locale getloc() const;
4
#
Returns: If no locale has been imbued, a copy of the global C++ locale, locale(), in effect at the time of construction.
Otherwise, returns the imbued locale, to be used to perform locale-dependent input and output operations.
🔗
static bool sync_with_stdio(bool sync = true);
1
#
Effects: If any input or output operation has occurred using the standard streams prior to the call, the effect is implementation-defined.
Otherwise, called with a false argument, it allows the standard streams to operate independently of the standard C streams.
2
#
Returns: true if the previous state of the standard iostream objects was synchronized and otherwise returns false.
The first time it is called, the function returns true.
3
#
Remarks: When a standard iostream object str is synchronized with a standard stdio stream f, the effect of inserting a character c by fputc(f, c); is the same as the effect of str.rdbuf()->sputc(c); for any sequences of characters; the effect of extracting a character c by c = fgetc(f); is the same as the effect of c = str.rdbuf()->sbumpc(); for any sequences of characters; and the effect of pushing back a character c by ungetc(c, f); is the same as the effect of str.rdbuf()->sputbackc(c); for any sequence of characters.251
251)251)
This implies that operations on a standard iostream object can be mixed arbitrarily with operations on the corresponding stdio stream.
In practical terms, synchronization usually means that a standard iostream object and a standard stdio object share a buffer.

31.5.2.6 Storage functions [ios.base.storage]

🔗
static int xalloc();
1
#
Returns: index ++.
2
#
Remarks: Concurrent access to this function by multiple threads does not result in a data race.
🔗
long& iword(int idx);
3
#
Effects: If iarray is a null pointer, allocates an array of long of unspecified size and stores a pointer to its first element in iarray.
The function then extends the array pointed at by iarray as necessary to include the element iarray[idx].
Each newly allocated element of the array is initialized to zero.
The reference returned is invalid after any other operation on the object.252
However, the value of the storage referred to is retained, so that until the next call to copyfmt, calling iword with the same index yields another reference to the same value.
If the function fails253 and *this is a base class subobject of a basic_ios<> object or subobject, the effect is equivalent to calling basic_ios<>​::​setstate(badbit) on the derived object (which may throw failure).
5
#
Returns: On success iarray[idx].
On failure, a valid long& initialized to 0.
🔗
void*& pword(int idx);
6
#
Effects: If parray is a null pointer, allocates an array of pointers to void of unspecified size and stores a pointer to its first element in parray.
The function then extends the array pointed at by parray as necessary to include the element parray[idx].
Each newly allocated element of the array is initialized to a null pointer.
The reference returned is invalid after any other operation on the object.
However, the value of the storage referred to is retained, so that until the next call to copyfmt, calling pword with the same index yields another reference to the same value.
If the function fails254 and *this is a base class subobject of a basic_ios<> object or subobject, the effect is equivalent to calling basic_ios<>​::​setstate(badbit) on the derived object (which may throw failure).
8
#
Returns: On success parray[idx].
On failure a valid void*& initialized to 0.
9
#
Remarks: After a subsequent call to pword(int) for the same object, the earlier return value may no longer be valid.
252)252)
An implementation is free to implement both the integer array pointed at by iarray and the pointer array pointed at by parray as sparse data structures, possibly with a one-element cache for each.
253)253)
For example, because it cannot allocate space.
254)254)
For example, because it cannot allocate space.
🔗
void register_callback(event_callback fn, int idx);
1
#
Preconditions: The function fn does not throw exceptions.
2
#
Effects: Registers the pair (fn, idx) such that during calls to imbue() ([ios.base.locales]), copyfmt(), or ~ios_base() ([ios.base.cons]), the function fn is called with argument idx.
Functions registered are called when an event occurs, in opposite order of registration.
Functions registered while a callback function is active are not called until the next event.
3
#
Remarks: Identical pairs are not merged.
A function registered twice will be called twice.

31.5.2.8 Constructors and destructor [ios.base.cons]

🔗
ios_base();
1
#
Effects: Each ios_base member has an indeterminate value after construction.
The object's members shall be initialized by calling basic_ios​::​init before the object's first use or before it is destroyed, whichever comes first; otherwise the behavior is undefined.
🔗
~ios_base();
2
#
Effects: Calls each registered callback pair (fn, idx) ([ios.base.callback]) as (*fn)(​erase_event, *this, idx) at such time that any ios_base member function called from within fn has well-defined results.
Then, any memory obtained is deallocated.

31.5.3 Class template fpos [fpos]

🔗
namespace std { template<class stateT> class fpos { public: / [fpos.members], members stateT state() const; void state(stateT); private: stateT st; / exposition only }; }
🔗
void state(stateT s);
1
#
Effects: Assigns s to st.
🔗
stateT state() const;
2
#
An fpos type specifies file position information.
It holds a state object whose type is equal to the template parameter stateT.
Type stateT shall meet the Cpp17DefaultConstructible (Table 30), Cpp17CopyConstructible (Table 32), Cpp17CopyAssignable (Table 34), and Cpp17Destructible (Table 35) requirements.
If is_trivially_copy_constructible_v<stateT> is true, then fpos<stateT> has a trivial copy constructor.
If is_trivially_copy_assignable_v<stateT> is true, then fpos<stateT> has a trivial copy assignment operator.
If is_trivially_destructible_v<stateT> is true, then fpos<stateT> has a trivial destructor.
In addition, the expressions shown in Table 141 are valid and have the indicated semantics.
In that table,
  • (1.1)
    P refers to a specialization of fpos,
  • (1.2)
    p and q refer to values of type P or const P,
  • (1.3)
    pl and ql refer to modifiable lvalues of type P,
  • (1.4)
    O refers to type streamoff, and
  • (1.5)
    o and o2 refer to values of type streamoff or const streamoff.
Table 141 — Position type requirements [tab:fpos.operations]
🔗
Expression
Return type
Operational
Assertion/note
🔗
semantics
pre-/post-condition
🔗
P(o)
P
converts from offset
Effects: Value-initializes the state object.
🔗
P p(o);
P p = o;
Effects: Value-initializes the state object.

Postconditions: p == P(o) is true.
🔗
P()
P
P(0)
🔗
P p;
P p(0);
🔗
O(p)
streamoff
converts to offset
P(O(p)) == p
🔗
p == q
bool
Remarks: For any two values o and o2, if p is obtained from o converted to P or from a copy of such P value and if q is obtained from o2 converted to P or from a copy of such P value, then p == q is true only if o == o2 is true.
🔗
p != q
bool
!(p == q)
🔗
p + o
P
+ offset
Remarks: With ql = p + o;, then: ql - o == p
🔗
pl += o
P&
+= offset
Remarks: With ql = pl; before the +=, then: pl - o == ql
🔗
p - o
P
- offset
Remarks: With ql = p - o;, then: ql + o == p
🔗
pl -= o
P&
-= offset
Remarks: With ql = pl; before the -=, then: pl + o == ql
🔗
o + p
convertible to P
p + o
P(o + p) == p + o
🔗
p - q
streamoff
distance
p == q + (p - q)
2
#
Stream operations that return a value of type traits​::​pos_type return P(O(-1) as an invalid value to signal an error.
If this value is used as an argument to any istream, ostream, or streambuf member that accepts a value of type traits​::​pos_type then the behavior of that function is undefined.

31.5.4 Class template basic_ios [ios]

🔗
namespace std { template<class charT, class traits = char_traits<charT>> class basic_ios : public ios_base { public: using char_type = charT; using int_type = traits::int_type; using pos_type = traits::pos_type; using off_type = traits::off_type; using traits_type = traits; / [iostate.flags], flags functions explicit operator bool() const; bool operator!() const; iostate rdstate() const; void clear(iostate state = goodbit); void setstate(iostate state); bool good() const; bool eof() const; bool fail() const; bool bad() const; iostate exceptions() const; void exceptions(iostate except); / [basic.ios.cons], constructor/destructor explicit basic_ios(basic_streambuf<charT, traits>* sb); virtual ~basic_ios(); / [basic.ios.members], members basic_ostream<charT, traits>* tie() const; basic_ostream<charT, traits>* tie(basic_ostream<charT, traits>* tiestr); basic_streambuf<charT, traits>* rdbuf() const; basic_streambuf<charT, traits>* rdbuf(basic_streambuf<charT, traits>* sb); basic_ios& copyfmt(const basic_ios& rhs); char_type fill() const; char_type fill(char_type ch); locale imbue(const locale& loc); char narrow(char_type c, char dfault) const; char_type widen(char c) const; basic_ios(const basic_ios&) = delete; basic_ios& operator=(const basic_ios&) = delete; protected: basic_ios(); void init(basic_streambuf<charT, traits>* sb); void move(basic_ios& rhs); void move(basic_ios&& rhs); void swap(basic_ios& rhs) noexcept; void set_rdbuf(basic_streambuf<charT, traits>* sb); }; }
🔗
explicit basic_ios(basic_streambuf<charT, traits>* sb);
1
#
Effects: Assigns initial values to its member objects by calling init(sb).
🔗
basic_ios();
2
#
Effects: Leaves its member objects uninitialized.
The object shall be initialized by calling basic_ios​::​init before its first use or before it is destroyed, whichever comes first; otherwise the behavior is undefined.
🔗
~basic_ios();
3
#
Remarks: The destructor does not destroy rdbuf().
🔗
void init(basic_streambuf<charT, traits>* sb);
4
#
Postconditions: The postconditions of this function are indicated in Table 142.
Table 142 — basic_ios​::​init() effects [tab:basic.ios.cons]
🔗
Element
Value
🔗
rdbuf()
sb
🔗
tie()
0
🔗
rdstate()
goodbit if sb is not a null pointer, otherwise badbit.
🔗
exceptions()
goodbit
🔗
flags()
skipws | dec
🔗
width()
0
🔗
precision()
6
🔗
fill()
widen(' ')
🔗
getloc()
a copy of the value returned by locale()
🔗
iarray
a null pointer
🔗
parray
a null pointer

31.5.4.3 Member functions [basic.ios.members]

🔗
basic_ostream<charT, traits>* tie() const;
1
#
Returns: An output sequence that is tied to (synchronized with) the sequence controlled by the stream buffer.
🔗
basic_ostream<charT, traits>* tie(basic_ostream<charT, traits>* tiestr);
2
#
Preconditions: If tiestr is not null, tiestr is not reachable by traversing the linked list of tied stream objects starting from tiestr->tie().
3
#
Returns: The previous value of tie().
🔗
basic_streambuf<charT, traits>* rdbuf() const;
5
#
Returns: A pointer to the streambuf associated with the stream.
🔗
basic_streambuf<charT, traits>* rdbuf(basic_streambuf<charT, traits>* sb);
6
#
Effects: Calls clear().
7
#
Returns: The previous value of rdbuf().
🔗
locale imbue(const locale& loc);
9
#
Effects: Calls ios_base​::​imbue(loc) and if rdbuf() != 0 then rdbuf()->pubimbue(loc).
10
#
Returns: The prior value of ios_base​::​imbue().
🔗
char narrow(char_type c, char dfault) const;
11
#
Returns: use_facet<ctype<char_type>>(getloc().narrow(c, dfault).
🔗
char_type widen(char c) const;
12
#
Returns: use_facet<ctype<char_type>>(getloc().widen(c).
🔗
char_type fill() const;
13
#
Returns: The character used to pad (fill) an output conversion to the specified field width.
🔗
char_type fill(char_type fillch);
14
#
Returns: The previous value of fill().
🔗
basic_ios& copyfmt(const basic_ios& rhs);
16
#
Effects: If (this == addressof(rhs)) is true does nothing.
Otherwise assigns to the member objects of *this the corresponding member objects of rhs as follows:
  • (16.1)
    calls each registered callback pair (fn, idx) as (*fn)(erase_event, *this, idx);
  • (16.2)
    then, assigns to the member objects of *this the corresponding member objects of rhs, except that
    • (16.2.1)
      rdstate(), rdbuf(), and exceptions() are left unchanged;
    • (16.2.2)
      the contents of arrays pointed at by pword and iword are copied, not the pointers themselves;255 and
    • (16.2.3)
      if any newly stored pointer values in *this point at objects stored outside the object rhs and those objects are destroyed when rhs is destroyed, the newly stored pointer values are altered to point at newly constructed copies of the objects;
  • (16.3)
    then, calls each callback pair that was copied from rhs as (*fn)(copyfmt_event, *this, idx);
  • (16.4)
    then, calls exceptions(rhs.exceptions().
17
#
[Note 1: 
The second pass through the callback pairs permits a copied pword value to be zeroed, or to have its referent deep copied or reference counted, or to have other special action taken.
— end note]
18
#
Returns: *this.
🔗
void move(basic_ios& rhs); void move(basic_ios&& rhs);
20
#
Postconditions: *this has the state that rhs had before the function call, except that rdbuf() returns nullptr.
rhs is in a valid but unspecified state, except that rhs.rdbuf() returns the same value as it returned before the function call, and rhs.tie() returns nullptr.
🔗
void swap(basic_ios& rhs) noexcept;
21
#
Effects: The states of *this and rhs are exchanged, except that rdbuf() returns the same value as it returned before the function call, and rhs.rdbuf() returns the same value as it returned before the function call.
🔗
void set_rdbuf(basic_streambuf<charT, traits>* sb);
22
#
Effects: Associates the basic_streambuf object pointed to by sb with this stream without calling clear().
24
#
Throws: Nothing.
255)255)
This suggests an infinite amount of copying, but the implementation can keep track of the maximum element of the arrays that is nonzero.

31.5.4.4 Flags functions [iostate.flags]

🔗
explicit operator bool() const;
1
#
Returns: !fail().
🔗
bool operator!() const;
2
#
Returns: fail().
🔗
iostate rdstate() const;
3
#
Returns: The error state of the stream buffer.
🔗
void clear(iostate state = goodbit);
4
#
Effects: If ((state | (rdbuf() ? goodbit : badbit)) & exceptions() == 0, returns.
Otherwise, the function throws an object of class ios_base​::​failure ([ios.failure]), constructed with implementation-defined argument values.
5
#
Postconditions: If rdbuf() != 0 then state == rdstate(); otherwise rdstate() == (state | ios_base​::​badbit).
🔗
void setstate(iostate state);
6
#
Effects: Calls clear(rdstate() | state) (which may throw ios_base​::​failure ([ios.failure])).
🔗
bool good() const;
7
#
Returns: rdstate() == 0.
🔗
bool eof() const;
8
#
Returns: true if eofbit is set in rdstate().
🔗
bool fail() const;
9
#
Returns: true if failbit or badbit is set in rdstate().256
🔗
bool bad() const;
10
#
Returns: true if badbit is set in rdstate().
🔗
iostate exceptions() const;
11
#
Returns: A mask that determines what elements set in rdstate() cause exceptions to be thrown.
🔗
void exceptions(iostate except);
12
#
Effects: Calls clear(rdstate().
13
#
Postconditions: except == exceptions().
256)256)
Checking badbit also for fail() is historical practice.

31.5.5 ios_base manipulators [std.ios.manip]

31.5.5.1 fmtflags manipulators [fmtflags.manip]

1
#
Each function specified in this subclause is a designated addressable function ([namespace.std]).
🔗
ios_base& boolalpha(ios_base& str);
2
#
Effects: Calls str.setf(ios_base​::​boolalpha).
3
#
Returns: str.
🔗
ios_base& noboolalpha(ios_base& str);
4
#
Effects: Calls str.unsetf(ios_base​::​boolalpha).
5
#
Returns: str.
🔗
ios_base& showbase(ios_base& str);
6
#
Effects: Calls str.setf(ios_base​::​showbase).
7
#
Returns: str.
🔗
ios_base& noshowbase(ios_base& str);
8
#
Effects: Calls str.unsetf(ios_base​::​showbase).
9
#
Returns: str.
🔗
ios_base& showpoint(ios_base& str);
10
#
Effects: Calls str.setf(ios_base​::​showpoint).
11
#
Returns: str.
🔗
ios_base& noshowpoint(ios_base& str);
12
#
Effects: Calls str.unsetf(ios_base​::​showpoint).
13
#
Returns: str.
🔗
ios_base& showpos(ios_base& str);
14
#
Effects: Calls str.setf(ios_base​::​showpos).
15
#
Returns: str.
🔗
ios_base& noshowpos(ios_base& str);
16
#
Effects: Calls str.unsetf(ios_base​::​showpos).
17
#
Returns: str.
🔗
ios_base& skipws(ios_base& str);
18
#
Effects: Calls str.setf(ios_base​::​skipws).
19
#
Returns: str.
🔗
ios_base& noskipws(ios_base& str);
20
#
Effects: Calls str.unsetf(ios_base​::​skipws).
21
#
Returns: str.
🔗
ios_base& uppercase(ios_base& str);
22
#
Effects: Calls str.setf(ios_base​::​uppercase).
23
#
Returns: str.
🔗
ios_base& nouppercase(ios_base& str);
24
#
Effects: Calls str.unsetf(ios_base​::​uppercase).
25
#
Returns: str.
🔗
ios_base& unitbuf(ios_base& str);
26
#
Effects: Calls str.setf(ios_base​::​unitbuf).
27
#
Returns: str.
🔗
ios_base& nounitbuf(ios_base& str);
28
#
Effects: Calls str.unsetf(ios_base​::​unitbuf).
29
#
Each function specified in this subclause is a designated addressable function ([namespace.std]).
🔗
ios_base& internal(ios_base& str);
2
#
Effects: Calls str.setf(ios_base​::​internal, ios_base​::​adjustfield).
3
#
Returns: str.
🔗
ios_base& left(ios_base& str);
4
#
Effects: Calls str.setf(ios_base​::​left, ios_base​::​adjustfield).
5
#
Returns: str.
🔗
ios_base& right(ios_base& str);
6
#
Effects: Calls str.setf(ios_base​::​right, ios_base​::​adjustfield).
7
#
Each function specified in this subclause is a designated addressable function ([namespace.std]).
🔗
ios_base& dec(ios_base& str);
2
#
Effects: Calls str.setf(ios_base​::​dec, ios_base​::​basefield).
3
#
Returns: str.257
🔗
ios_base& hex(ios_base& str);
4
#
Effects: Calls str.setf(ios_base​::​hex, ios_base​::​basefield).
5
#
Returns: str.
🔗
ios_base& oct(ios_base& str);
6
#
Effects: Calls str.setf(ios_base​::​oct, ios_base​::​basefield).
7
#
Returns: str.
257)257)
The function signature dec(ios_base&) can be called by the function signature basic_ostream& stream​::​operator<(ios_base& (*)(ios_base&) to permit expressions of the form cout << dec to change the format flags stored in cout.

31.5.5.4 floatfield manipulators [floatfield.manip]

1
#
Each function specified in this subclause is a designated addressable function ([namespace.std]).
🔗
ios_base& fixed(ios_base& str);
2
#
Effects: Calls str.setf(ios_base​::​fixed, ios_base​::​floatfield).
3
#
Returns: str.
🔗
ios_base& scientific(ios_base& str);
4
#
Effects: Calls str.setf(ios_base​::​scientific, ios_base​::​floatfield).
5
#
Returns: str.
🔗
ios_base& hexfloat(ios_base& str);
6
#
Effects: Calls str.setf(ios_base​::​fixed | ios_base​::​scientific, ios_base​::​floatfield).
7
#
[Note 1: 
ios_base​::​hex cannot be used to specify a hexadecimal floating-point format, because it is not part of ios_base​::​floatfield (Table 137).
— end note]
🔗
ios_base& defaultfloat(ios_base& str);
9
#
Returns: str.

31.5.6 Error reporting [error.reporting]

🔗
error_code make_error_code(io_errc e) noexcept;
1
#
Returns: error_code(static_cast<int>(e), iostream_category().
🔗
error_condition make_error_condition(io_errc e) noexcept;
2
#
Returns: error_condition(static_cast<int>(e), iostream_category().
🔗
const error_category& iostream_category() noexcept;
3
#
Returns: A reference to an object of a type derived from class error_category.
4
#
The object's default_error_condition and equivalent virtual functions shall behave as specified for the class error_category.
The object's name virtual function shall return a pointer to the string "iostream".

31.6 Stream buffers [stream.buffers]

31.6.1 Header <streambuf> synopsis [streambuf.syn]

🔗
namespace std { / [streambuf], class template basic_streambuf template<class charT, class traits = char_traits<charT>> class basic_streambuf; using streambuf = basic_streambuf<char>; using wstreambuf = basic_streambuf<wchar_t>; }
1
#
The header <streambuf> defines types that control input from and output to character sequences.

31.6.2 Stream buffer requirements [streambuf.reqts]

1
#
Stream buffers can impose various constraints on the sequences they control.
Some constraints are:
  • (1.1)
    The controlled input sequence can be not readable.
  • (1.2)
    The controlled output sequence can be not writable.
  • (1.3)
    The controlled sequences can be associated with the contents of other representations for character sequences, such as external files.
  • (1.4)
    The controlled sequences can support operations directly to or from associated sequences.
  • (1.5)
    The controlled sequences can impose limitations on how the program can read characters from a sequence, write characters to a sequence, put characters back into an input sequence, or alter the stream position.
2
#
Each sequence is characterized by three pointers which, if non-null, all point into the same charT array object.
The array object represents, at any moment, a (sub)sequence of characters from the sequence.
Operations performed on a sequence alter the values stored in these pointers, perform reads and writes directly to or from associated sequences, and alter “the stream position” and conversion state as needed to maintain this subsequence relationship.
The three pointers are:
  • (2.1)
    the beginning pointer, or lowest element address in the array (called xbeg here);
  • (2.2)
    the next pointer, or next element address that is a current candidate for reading or writing (called xnext here);
  • (2.3)
    the end pointer, or first element address beyond the end of the array (called xend here).
3
#
The following semantic constraints shall always apply for any set of three pointers for a sequence, using the pointer names given immediately above:
  • (3.1)
    If xnext is not a null pointer, then xbeg and xend shall also be non-null pointers into the same charT array, as described above; otherwise, xbeg and xend shall also be null.
  • (3.2)
    If xnext is not a null pointer and xnext < xend for an output sequence, then a write position is available.
    In this case, *xnext shall be assignable as the next element to write (to put, or to store a character value, into the sequence).
  • (3.3)
    If xnext is not a null pointer and xbeg < xnext for an input sequence, then a putback position is available.
    In this case, xnext[-1] shall have a defined value and is the next (preceding) element to store a character that is put back into the input sequence.
  • (3.4)
    If xnext is not a null pointer and xnext < xend for an input sequence, then a read position is available.
    In this case, *xnext shall have a defined value and is the next element to read (to get, or to obtain a character value, from the sequence).

31.6.3 Class template basic_streambuf [streambuf]

🔗
namespace std { template<class charT, class traits = char_traits<charT>> class basic_streambuf { public: using char_type = charT; using int_type = traits::int_type; using pos_type = traits::pos_type; using off_type = traits::off_type; using traits_type = traits; virtual ~basic_streambuf(); / [streambuf.locales], locales locale pubimbue(const locale& loc); locale getloc() const; / [streambuf.buffer], buffer and positioning basic_streambuf* pubsetbuf(char_type* s, streamsize n); pos_type pubseekoff(off_type off, ios_base::seekdir way, ios_base::openmode which = ios_base::in | ios_base::out); pos_type pubseekpos(pos_type sp, ios_base::openmode which = ios_base::in | ios_base::out); int pubsync(); / get and put areas / [streambuf.pub.get], get area streamsize in_avail(); int_type snextc(); int_type sbumpc(); int_type sgetc(); streamsize sgetn(char_type* s, streamsize n); / [streambuf.pub.pback], putback int_type sputbackc(char_type c); int_type sungetc(); / [streambuf.pub.put], put area int_type sputc(char_type c); streamsize sputn(const char_type* s, streamsize n); protected: basic_streambuf(); basic_streambuf(const basic_streambuf& rhs); basic_streambuf& operator=(const basic_streambuf& rhs); void swap(basic_streambuf& rhs); / [streambuf.get.area], get area access char_type* eback() const; char_type* gptr() const; char_type* egptr() const; void gbump(int n); void setg(char_type* gbeg, char_type* gnext, char_type* gend); / [streambuf.put.area], put area access char_type* pbase() const; char_type* pptr() const; char_type* epptr() const; void pbump(int n); void setp(char_type* pbeg, char_type* pend); / [streambuf.virtuals], virtual functions / [streambuf.virt.locales], locales virtual void imbue(const locale& loc); / [streambuf.virt.buffer], buffer management and positioning virtual basic_streambuf* setbuf(char_type* s, streamsize n); virtual pos_type seekoff(off_type off, ios_base::seekdir way, ios_base::openmode which = ios_base::in | ios_base::out); virtual pos_type seekpos(pos_type sp, ios_base::openmode which = ios_base::in | ios_base::out); virtual int sync(); / [streambuf.virt.get], get area virtual streamsize showmanyc(); virtual streamsize xsgetn(char_type* s, streamsize n); virtual int_type underflow(); virtual int_type uflow(); / [streambuf.virt.pback], putback virtual int_type pbackfail(int_type c = traits::eof(); / [streambuf.virt.put], put area virtual streamsize xsputn(const char_type* s, streamsize n); virtual int_type overflow(int_type c = traits::eof(); }; }
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The class template basic_streambuf serves as a base class for deriving various stream buffers whose objects each control two character sequences:
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basic_streambuf();
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Effects: Initializes:258
  • (1.1)
    all pointer member objects to null pointers,
  • (1.2)
    the getloc() member to a copy of the global locale, locale(), at the time of construction.
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Remarks: Once the getloc() member is initialized, results of calling locale member functions, and of members of facets so obtained, can safely be cached until the next time the member imbue is called.
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basic_streambuf(const basic_streambuf& rhs);
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Postconditions:
  • (3.1)
    eback() == rhs.eback()
  • (3.2)
    gptr() == rhs.gptr()
  • (3.3)
    egptr() == rhs.egptr()
  • (3.4)
    pbase() == rhs.pbase()
  • (3.5)
    pptr() == rhs.pptr()
  • (3.6)
    epptr() == rhs.epptr()
  • (3.7)
    getloc() == rhs.getloc()
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~basic_streambuf();
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Effects: None.
258)258)
The default constructor is protected for class basic_streambuf to assure that only objects for classes derived from this class can be constructed.

31.6.3.3 Public member functions [streambuf.members]

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locale pubimbue(const locale& loc);
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Effects: Calls imbue(loc).
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Returns: Previous value of getloc().
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locale getloc() const;
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Returns: If pubimbue() has ever been called, then the last value of loc supplied, otherwise the current global locale, locale(), in effect at the time of construction.
If called after pubimbue() has been called but before pubimbue has returned (i.e., from within the call of imbue()) then it returns the previous value.

31.6.3.3.2 Buffer management and positioning [streambuf.buffer]

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basic_streambuf* pubsetbuf(char_type* s, streamsize n);
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Returns: setbuf(s, n).
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pos_type pubseekoff(off_type off, ios_base::seekdir way, ios_base::openmode which = ios_base::in | ios_base::out);
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Returns: seekoff(off, way, which).
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pos_type pubseekpos(pos_type sp, ios_base::openmode which = ios_base::in | ios_base::out);
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Returns: seekpos(sp, which).
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int pubsync();
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Returns: sync().
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streamsize in_avail();
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Returns: If a read position is available, returns egptr() - gptr().
Otherwise returns showmanyc().
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int_type snextc();
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Effects: Calls sbumpc().
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Returns: If that function returns traits​::​eof(), returns traits​::​eof().
Otherwise, returns sgetc().
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int_type sbumpc();
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Effects: If the input sequence read position is not available, returns uflow().
Otherwise, returns traits​::​to_int_type(*gptr() and increments the next pointer for the input sequence.
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int_type sgetc();
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Returns: If the input sequence read position is not available, returns underflow().
Otherwise, returns traits​::​to_int_type(*gptr().
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streamsize sgetn(char_type* s, streamsize n);
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Returns: xsgetn(s, n).
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int_type sputbackc(char_type c);
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Effects: If the input sequence putback position is not available, or if traits​::​eq(c, gptr()[-1]) is false, returns pbackfail(traits​::​to_int_type(c)).
Otherwise, decrements the next pointer for the input sequence and returns traits​::​to_int_type(*gptr().
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int_type sungetc();
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Effects: If the input sequence putback position is not available, returns pbackfail().
Otherwise, decrements the next pointer for the input sequence and returns traits​::​to_int_type(*gptr().
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int_type sputc(char_type c);
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Effects: If the output sequence write position is not available, returns overflow(traits​::​to_int_type(c)).
Otherwise, stores c at the next pointer for the output sequence, increments the pointer, and returns traits​::​to_int_type(c).
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streamsize sputn(const char_type* s, streamsize n);
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Returns: xsputn(s, n).

31.6.3.4 Protected member functions [streambuf.protected]

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basic_streambuf& operator=(const basic_streambuf& rhs);
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Returns: *this.
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void swap(basic_streambuf& rhs);
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Effects: Swaps the data members of rhs and *this.
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char_type* eback() const;
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Returns: The beginning pointer for the input sequence.
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char_type* gptr() const;
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Returns: The next pointer for the input sequence.
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char_type* egptr() const;
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Returns: The end pointer for the input sequence.
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void gbump(int n);
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Effects: Adds n to the next pointer for the input sequence.
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void setg(char_type* gbeg, char_type* gnext, char_type* gend);
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Preconditions: [gbeg, gnext), [gbeg, gend), and [gnext, gend) are all valid ranges.
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Postconditions: gbeg == eback(), gnext == gptr(), and gend == egptr() are all true.
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char_type* pbase() const;
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Returns: The beginning pointer for the output sequence.
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char_type* pptr() const;
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Returns: The next pointer for the output sequence.
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char_type* epptr() const;
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Returns: The end pointer for the output sequence.
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void pbump(int n);
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Effects: Adds n to the next pointer for the output sequence.
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void setp(char_type* pbeg, char_type* pend);
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Postconditions: pbeg == pbase(), pbeg == pptr(), and pend == epptr() are all true.

31.6.3.5 Virtual functions [streambuf.virtuals]

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void imbue(const locale&);
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Remarks: Allows the derived class to be informed of changes in locale at the time they occur.
Between invocations of this function a class derived from streambuf can safely cache results of calls to locale functions and to members of facets so obtained.
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Default behavior: Does nothing.

31.6.3.5.2 Buffer management and positioning [streambuf.virt.buffer]

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basic_streambuf* setbuf(char_type* s, streamsize n);
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Effects: Influences stream buffering in a way that is defined separately for each class derived from basic_streambuf in this Clause ([stringbuf.virtuals], [filebuf.virtuals]).
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Default behavior: Does nothing.
Returns this.
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pos_type seekoff(off_type off, ios_base::seekdir way, ios_base::openmode which = ios_base::in | ios_base::out);
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Effects: Alters the stream positions within one or more of the controlled sequences in a way that is defined separately for each class derived from basic_streambuf in this Clause ([stringbuf.virtuals], [filebuf.virtuals]).
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Default behavior: Returns pos_type(off_type(-1).
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pos_type seekpos(pos_type sp, ios_base::openmode which = ios_base::in | ios_base::out);
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Effects: Alters the stream positions within one or more of the controlled sequences in a way that is defined separately for each class derived from basic_streambuf in this Clause ([stringbuf], [filebuf]).
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Default behavior: Returns pos_type(off_type(-1).
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int sync();
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Effects: Synchronizes the controlled sequences with the arrays.
That is, if pbase() is non-null the characters between pbase() and pptr() are written to the controlled sequence.
The pointers may then be reset as appropriate.
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Default behavior: Returns zero.
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streamsize showmanyc();259
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Returns: An estimate of the number of characters available in the sequence, or
If it returns a positive value, then successive calls to underflow() will not return traits​::​eof() until at least that number of characters have been extracted from the stream.
If showmanyc() returns
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Remarks: Uses traits​::​eof().
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streamsize xsgetn(char_type* s, streamsize n);
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Effects: Assigns up to n characters to successive elements of the array whose first element is designated by s.
The characters assigned are read from the input sequence as if by repeated calls to sbumpc().
Assigning stops when either n characters have been assigned or a call to sbumpc() would return traits​::​eof().
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Remarks: Uses traits​::​eof().
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int_type underflow();
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The pending sequence of characters is defined as the concatenation of
  • (7.1)
    the empty sequence if gptr() is null, otherwise the characters in [gptr(), egptr()), followed by
  • (7.2)
    some (possibly empty) sequence of characters read from the input sequence.
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The result character is the first character of the pending sequence if it is non-empty, otherwise the next character that would be read from the input sequence.
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The backup sequence is the empty sequence if eback() is null, otherwise the characters in [eback(), gptr()).
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Effects: The function sets up the gptr() and egptr() such that if the pending sequence is non-empty, then egptr() is non-null and the characters in [gptr(), egptr()) are the characters in the pending sequence, otherwise either gptr() is null or gptr() == egptr().
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If eback() and gptr() are non-null then the function is not constrained as to their contents, but the “usual backup condition” is that either
  • (11.1)
    the backup sequence contains at least gptr() - eback() characters, in which case the characters in [eback(), gptr()) agree with the last gptr() - eback() characters of the backup sequence, or
  • (11.2)
    the characters in [gptr() - n, gptr()) agree with the backup sequence (where n is the length of the backup sequence).
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Returns: traits​::​to_int_type(c), where c is the first character of the pending sequence, without moving the input sequence position past it.
If the pending sequence is null then the function returns traits​::​eof() to indicate failure.
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Default behavior: Returns traits​::​eof().
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Remarks: The public members of basic_streambuf call this virtual function only if gptr() is null or gptr() >= egptr().
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int_type uflow();
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Preconditions: The constraints are the same as for underflow(), except that the result character is transferred from the pending sequence to the backup sequence, and the pending sequence is not empty before the transfer.
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Default behavior: Calls underflow().
If underflow() returns traits​::​eof(), returns traits​::​eof().
Otherwise, returns the value of traits​::​to_int_type(*gptr() and increments the value of the next pointer for the input sequence.
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Returns: traits​::​eof() to indicate failure.
259)259)
The morphemes of showmanyc are “es-how-many-see”, not “show-manic”.
260)260)
underflow or uflow can fail by throwing an exception prematurely.
The intention is not only that the calls will not return eof() but that they will return “immediately”.
261)261)
Classes derived from basic_streambuf can provide more efficient ways to implement xsgetn() and xsputn() by overriding these definitions from the base class.
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int_type pbackfail(int_type c = traits::eof();
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The pending sequence is defined as for underflow(), with the modifications that
  • (1.1)
    If traits​::​eq_int_type(c, traits​::​eof() returns true, then the input sequence is backed up one character before the pending sequence is determined.
  • (1.2)
    If traits​::​eq_int_type(c, traits​::​eof() returns false, then c is prepended.
    Whether the input sequence is backed up or modified in any other way is unspecified.
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Postconditions: On return, the constraints of gptr(), eback(), and pptr() are the same as for underflow().
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Returns: traits​::​eof() to indicate failure.
Failure may occur because the input sequence could not be backed up, or if for some other reason the pointers cannot be set consistent with the constraints.
pbackfail() is called only when put back has really failed.
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Returns some value other than traits​::​eof() to indicate success.
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Default behavior: Returns traits​::​eof().
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Remarks: The public functions of basic_streambuf call this virtual function only when gptr() is null, gptr() == eback(), or traits​::​eq(traits​::​to_char_type(c), gptr()[-1]) returns false.
Other calls shall also satisfy that constraint.
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streamsize xsputn(const char_type* s, streamsize n);
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Effects: Writes up to n characters to the output sequence as if by repeated calls to sputc(c).
The characters written are obtained from successive elements of the array whose first element is designated by s.
Writing stops when either n characters have been written or a call to sputc(c) would return traits​::​eof().
It is unspecified whether the function calls overflow() when pptr() == epptr() becomes true or whether it achieves the same effects by other means.
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Returns: The number of characters written.
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int_type overflow(int_type c = traits::eof();
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Effects: Consumes some initial subsequence of the characters of the pending sequence.
The pending sequence is defined as the concatenation of
  • (3.1)
    the empty sequence if pbase() is null, otherwise the pptr() - pbase() characters beginning at pbase(), followed by
  • (3.2)
    the empty sequence if traits​::​eq_int_type(c, traits​::​eof() returns true, otherwise the sequence consisting of c.
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Preconditions: Every overriding definition of this virtual function obeys the following constraints:
  • (4.1)
    The effect of consuming a character on the associated output sequence is specified.262
  • (4.2)
    Let r be the number of characters in the pending sequence not consumed.
    If r is nonzero then pbase() and pptr() are set so that: pptr() - pbase() == r and the r characters starting at pbase() are the associated output stream.
    In case r is zero (all characters of the pending sequence have been consumed) then either pbase() is set to nullptr, or pbase() and pptr() are both set to the same non-null value.
  • (4.3)
    The function may fail if either appending some character to the associated output stream fails or if it is unable to establish pbase() and pptr() according to the above rules.
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Returns: traits​::​eof() or throws an exception if the function fails.
Otherwise, returns some value other than traits​::​eof() to indicate success.263
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Default behavior: Returns traits​::​eof().
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Remarks: The member functions sputc() and sputn() call this function in case that no room can be found in the put buffer enough to accommodate the argument character sequence.
262)262)
That is, for each class derived from a specialization of basic_streambuf in this Clause ([stringbuf], [filebuf]), a specification of how consuming a character affects the associated output sequence is given.
There is no requirement on a program-defined class.
263)263)
Typically, overflow returns c to indicate success, except when traits​::​eq_int_type(c, traits​::​eof() returns true, in which case it returns traits​::​not_eof(c).

31.7 Formatting and manipulators [iostream.format]

31.7.1 Header <istream> synopsis [istream.syn]

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namespace std { / [istream], class template basic_istream template<class charT, class traits = char_traits<charT>> class basic_istream; using istream = basic_istream<char>; using wistream = basic_istream<wchar_t>; / [iostreamclass], class template basic_iostream template<class charT, class traits = char_traits<charT>> class basic_iostream; using iostream = basic_iostream<char>; using wiostream = basic_iostream<wchar_t>; / [istream.manip], standard basic_istream manipulators template<class charT, class traits> basic_istream<charT, traits>& ws(basic_istream<charT, traits>& is); / [istream.rvalue], rvalue stream extraction template<class Istream, class T> Istream&& operator>(Istream&& is, T&& x); }

31.7.2 Header <ostream> synopsis [ostream.syn]

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namespace std { / [ostream], class template basic_ostream template<class charT, class traits = char_traits<charT>> class basic_ostream; using ostream = basic_ostream<char>; using wostream = basic_ostream<wchar_t>; / [ostream.manip], standard basic_ostream manipulators template<class charT, class traits> basic_ostream<charT, traits>& endl(basic_ostream<charT, traits>& os); template<class charT, class traits> basic_ostream<charT, traits>& ends(basic_ostream<charT, traits>& os); template<class charT, class traits> basic_ostream<charT, traits>& flush(basic_ostream<charT, traits>& os); template<class charT, class traits> basic_ostream<charT, traits>& emit_on_flush(basic_ostream<charT, traits>& os); template<class charT, class traits> basic_ostream<charT, traits>& noemit_on_flush(basic_ostream<charT, traits>& os); template<class charT, class traits> basic_ostream<charT, traits>& flush_emit(basic_ostream<charT, traits>& os); / [ostream.rvalue], rvalue stream insertion template<class Ostream, class T> Ostream&& operator<(Ostream&& os, const T& x); / [ostream.formatted.print], print functions template<class. Args> void print(ostream& os, format_string<Args..> fmt, Args&&. args); template<class. Args> void println(ostream& os, format_string<Args..> fmt, Args&&. args); void println(ostream& os); void vprint_unicode(ostream& os, string_view fmt, format_args args); void vprint_nonunicode(ostream& os, string_view fmt, format_args args); }

31.7.3 Header <iomanip> synopsis [iomanip.syn]

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namespace std { / [std.manip], standard manipulators unspecified resetiosflags(ios_base::fmtflags mask); unspecified setiosflags (ios_base::fmtflags mask); unspecified setbase(int base); template<class charT> unspecified setfill(charT c); unspecified setprecision(int n); unspecified setw(int n); / [ext.manip], extended manipulators template<class moneyT> unspecified get_money(moneyT& mon, bool intl = false); template<class moneyT> unspecified put_money(const moneyT& mon, bool intl = false); template<class charT> unspecified get_time(tm* tmb, const charT* fmt); template<class charT> unspecified put_time(const tm* tmb, const charT* fmt); / [quoted.manip], quoted manipulators template<class charT> unspecified quoted(const charT* s, charT delim = charT('"'), charT escape = charT('\\'); template<class charT, class traits, class Allocator> unspecified quoted(const basic_string<charT, traits, Allocator>& s, charT delim = charT('"'), charT escape = charT('\\'); template<class charT, class traits, class Allocator> unspecified quoted(basic_string<charT, traits, Allocator>& s, charT delim = charT('"'), charT escape = charT('\\'); template<class charT, class traits> unspecified quoted(basic_string_view<charT, traits> s, charT delim = charT('"'), charT escape = charT('\\'); }

31.7.4 Header <print> synopsis [print.syn]

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namespace std { / [print.fun], print functions template<class. Args> void print(format_string<Args..> fmt, Args&&. args); template<class. Args> void print(FILE* stream, format_string<Args..> fmt, Args&&. args); template<class. Args> void println(format_string<Args..> fmt, Args&&. args); void println(); template<class. Args> void println(FILE* stream, format_string<Args..> fmt, Args&&. args); void println(FILE* stream); void vprint_unicode(string_view fmt, format_args args); void vprint_unicode(FILE* stream, string_view fmt, format_args args); void vprint_unicode_buffered(FILE* stream, string_view fmt, format_args args); void vprint_nonunicode(string_view fmt, format_args args); void vprint_nonunicode(FILE* stream, string_view fmt, format_args args); void vprint_nonunicode_buffered(FILE* stream, string_view fmt, format_args args); }

31.7.5 Input streams [input.streams]

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The header <istream> defines two class templates and a function template that control input from a stream buffer, along with a function template that extracts from stream rvalues.

31.7.5.2 Class template basic_istream [istream]

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When a function is specified with a type placeholder of extended-floating-point-type, the implementation provides overloads for all cv-unqualified extended floating-point types ([basic.fundamental]) in lieu of extended-floating-​point-type.
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namespace std { template<class charT, class traits = char_traits<charT>> class basic_istream : virtual public basic_ios<charT, traits> { public: / types (inherited from basic_ios) using char_type = charT; using int_type = traits::int_type; using pos_type = traits::pos_type; using off_type = traits::off_type; using traits_type = traits; / [istream.cons], constructor/destructor explicit basic_istream(basic_streambuf<charT, traits>* sb); virtual ~basic_istream(); / [istream.sentry], prefix/suffix class sentry; / [istream.formatted], formatted input basic_istream& operator>(basic_istream& (*pf)(basic_istream&); basic_istream& operator>(basic_ios<charT, traits>& (*pf)(basic_ios<charT, traits>&); basic_istream& operator>(ios_base& (*pf)(ios_base&); basic_istream& operator>(bool& n); basic_istream& operator>(short& n); basic_istream& operator>(unsigned short& n); basic_istream& operator>(int& n); basic_istream& operator>(unsigned int& n); basic_istream& operator>(long& n); basic_istream& operator>(unsigned long& n); basic_istream& operator>(long long& n); basic_istream& operator>(unsigned long& n); basic_istream& operator>(float& f); basic_istream& operator>(double& f); basic_istream& operator>(long double& f); basic_istream& operator>(extended-floating-point-type& f); basic_istream& operator>(void*& p); basic_istream& operator>(basic_streambuf<char_type, traits>* sb); / [istream.unformatted], unformatted input streamsize gcount() const; int_type get(); basic_istream& get(char_type& c); basic_istream& get(char_type* s, streamsize n); basic_istream& get(char_type* s, streamsize n, char_type delim); basic_istream& get(basic_streambuf<char_type, traits>& sb); basic_istream& get(basic_streambuf<char_type, traits>& sb, char_type delim); basic_istream& getline(char_type* s, streamsize n); basic_istream& getline(char_type* s, streamsize n, char_type delim); basic_istream& ignore(streamsize n = 1, int_type delim = traits::eof(); basic_istream& ignore(streamsize n, char_type delim); int_type peek(); basic_istream& read (char_type* s, streamsize n); streamsize readsome(char_type* s, streamsize n); basic_istream& putback(char_type c); basic_istream& unget(); int sync(); pos_type tellg(); basic_istream& seekg(pos_type); basic_istream& seekg(off_type, ios_base::seekdir); protected: / [istream.cons], copy/move constructor basic_istream(const basic_istream&) = delete; basic_istream(basic_istream&& rhs); / [istream.assign], assignment and swap basic_istream& operator=(const basic_istream&) = delete; basic_istream& operator=(basic_istream&& rhs); void swap(basic_istream& rhs); }; / [istream.extractors], character extraction templates template<class charT, class traits> basic_istream<charT, traits>& operator>(basic_istream<charT, traits>&, charT&); template<class traits> basic_istream<char, traits>& operator>(basic_istream<char, traits>&, unsigned char&); template<class traits> basic_istream<char, traits>& operator>(basic_istream<char, traits>&, signed char&); template<class charT, class traits, size_t N> basic_istream<charT, traits>& operator>(basic_istream<charT, traits>&, charT(&)[N]); template<class traits, size_t N> basic_istream<char, traits>& operator>(basic_istream<char, traits>&, unsigned char(&)[N]); template<class traits, size_t N> basic_istream<char, traits>& operator>(basic_istream<char, traits>&, signed char(&)[N]); }
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The class template basic_istream defines a number of member function signatures that assist in reading and interpreting input from sequences controlled by a stream buffer.
3
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Two groups of member function signatures share common properties: the formatted input functions (or extractors) and the unformatted input functions. Both groups of input functions are described as if they obtain (or extract) input characters by calling rdbuf()->sbumpc() or rdbuf()->sgetc().
They may use other public members of istream.
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explicit basic_istream(basic_streambuf<charT, traits>* sb);
1
#
Effects: Initializes the base class subobject with basic_ios​::​init(sb) ([basic.ios.cons]).
2
#
Postconditions: gcount() == 0.
🔗
basic_istream(basic_istream&& rhs);
3
#
Effects: Default constructs the base class, copies the gcount() from rhs, calls basic_ios<charT, traits>​::​move(rhs) to initialize the base class, and sets the gcount() for rhs to 0.
🔗
virtual ~basic_istream();
4
#
Remarks: Does not perform any operations of rdbuf().

31.7.5.2.3 Assignment and swap [istream.assign]

🔗
basic_istream& operator=(basic_istream&& rhs);
1
#
Returns: *this.
🔗
void swap(basic_istream& rhs);
3
#
Effects: Calls basic_ios<charT, traits>​::​swap(rhs).
Exchanges the values returned by gcount() and rhs.gcount().

31.7.5.2.4 Class basic_istream​::​sentry [istream.sentry]

🔗
namespace std { template<class charT, class traits> class basic_istream<charT, traits>::sentry { bool ok_; / exposition only public: explicit sentry(basic_istream& is, bool noskipws = false); ~sentry(); explicit operator bool() const { return ok_; } sentry(const sentry&) = delete; sentry& operator=(const sentry&) = delete; }; }
1
#
The class sentry defines a class that is responsible for doing exception safe prefix and suffix operations.
🔗
explicit sentry(basic_istream& is, bool noskipws = false);
2
#
Effects: If is.good() is false, calls is.setstate(failbit).
Otherwise, prepares for formatted or unformatted input.
First, if is.tie() is not a null pointer, the function calls is.tie()->flush() to synchronize the output sequence with any associated external C stream.
Except that this call can be suppressed if the put area of is.tie() is empty.
Further an implementation is allowed to defer the call to flush until a call of is.rdbuf()->underflow() occurs.
If no such call occurs before the sentry object is destroyed, the call to flush may be eliminated entirely.264
If noskipws is zero and is.flags() & ios_base​::​skipws is nonzero, the function extracts and discards each character as long as the next available input character c is a whitespace character.
If is.rdbuf()->sbumpc() or is.rdbuf()->sgetc() returns traits​::​eof(), the function calls setstate(failbit | eofbit) (which may throw ios_base​::​failure).
3
#
Remarks: The constructor explicit sentry(basic_istream& is, bool noskipws = false) uses the currently imbued locale in is, to determine whether the next input character is whitespace or not.
4
#
To decide if the character c is a whitespace character, the constructor performs as if it executes the following code fragment: const ctype<charT>& ctype = use_facet<ctype<charT>>(is.getloc(); if (ctype.is(ctype.space, c) != 0) / c is a whitespace character.
5
#
If, after any preparation is completed, is.good() is true, ok_ != false otherwise, ok_ == false.
During preparation, the constructor may call setstate(failbit) (which may throw ios_base​::​​failure ([iostate.flags])).265
🔗
~sentry();
6
#
Effects: None.
🔗
explicit operator bool() const;
7
#
Returns: ok_.
264)264)
This will be possible only in functions that are part of the library.
The semantics of the constructor used in user code is as specified.
265)265)
The sentry constructor and destructor can also perform additional implementation-dependent operations.

31.7.5.3 Formatted input functions [istream.formatted]

1
#
Each formatted input function begins execution by constructing an object of type ios_base​::​iostate, termed the local error state, and initializing it to ios_base​::​goodbit.
It then creates an object of class sentry with the noskipws (second) argument false.
If the sentry object returns true, when converted to a value of type bool, the function endeavors to obtain the requested input.
Otherwise, if the sentry constructor exits by throwing an exception or if the sentry object produces false when converted to a value of type bool, the function returns without attempting to obtain any input.
If rdbuf()->sbumpc() or rdbuf()->sgetc() returns traits​::​eof(), then ios_base​::​eofbit is set in the local error state and the input function stops trying to obtain the requested input.
If an exception is thrown during input then ios_base​::​badbit is set in the local error state, *this's error state is set to the local error state, and the exception is rethrown if (exceptions() & badbit) != 0.
After extraction is done, the input function calls setstate, which sets *this's error state to the local error state, and may throw an exception.
In any case, the formatted input function destroys the sentry object.
If no exception has been thrown, it returns *this.
🔗
basic_istream& operator>(unsigned short& val); basic_istream& operator>(unsigned int& val); basic_istream& operator>(long& val); basic_istream& operator>(unsigned long& val); basic_istream& operator>(long long& val); basic_istream& operator>(unsigned long& val); basic_istream& operator>(float& val); basic_istream& operator>(double& val); basic_istream& operator>(long double& val); basic_istream& operator>(bool& val); basic_istream& operator>(void*& val);
1
#
As in the case of the inserters, these extractors depend on the locale's num_get<> object to perform parsing the input stream data.
These extractors behave as formatted input functions (as described in [istream.formatted.reqmts]).
After a sentry object is constructed, the conversion occurs as if performed by the following code fragment, where state represents the input function's local error state: using numget = num_get<charT, istreambuf_iterator<charT, traits>>; use_facet<numget>(loc).get(*this, 0, *this, state, val);
In the above fragment, loc stands for the private member of the basic_ios class.
[Note 1: 
The first argument provides an object of the istreambuf_iterator class which is an iterator pointed to an input stream.
It bypasses istreams and uses streambufs directly.
— end note]
Class locale relies on this type as its interface to istream, so that it does not need to depend directly on istream.
🔗
basic_istream& operator>(short& val);
2
#
The conversion occurs as if performed by the following code fragment (using the same notation as for the preceding code fragment): using numget = num_get<charT, istreambuf_iterator<charT, traits>>; long lval; use_facet<numget>(loc).get(*this, 0, *this, state, lval); if (lval < numeric_limits<short>::min() { state |= ios_base::failbit; val = numeric_limits<short>::min(); } else if (numeric_limits<short>::max() < lval) { state |= ios_base::failbit; val = numeric_limits<short>::max(); } else val = static_cast<short>(lval);
🔗
basic_istream& operator>(int& val);
3
#
The conversion occurs as if performed by the following code fragment (using the same notation as for the preceding code fragment): using numget = num_get<charT, istreambuf_iterator<charT, traits>>; long lval; use_facet<numget>(loc).get(*this, 0, *this, state, lval); if (lval < numeric_limits<int>::min() { state |= ios_base::failbit; val = numeric_limits<int>::min(); } else if (numeric_limits<int>::max() < lval) { state |= ios_base::failbit; val = numeric_limits<int>::max(); } else val = static_cast<int>(lval);
🔗
basic_istream& operator>(extended-floating-point-type& val);
4
#
If the floating-point conversion rank of extended-floating-point-type is not less than or equal to that of long double, then an invocation of the operator function is conditionally supported with implementation-defined semantics.
5
#
Otherwise, let FP be a standard floating-point type:
  • (5.1)
    if the floating-point conversion rank of extended-floating-point-type is less than or equal to that of float, then FP is float,
  • (5.2)
    otherwise, if the floating-point conversion rank of extended-floating-point-type is less than or equal to that of double, then FP is double,
  • (5.3)
    otherwise, FP is long double.
6
#
The conversion occurs as if performed by the following code fragment (using the same notation as for the preceding code fragment): using numget = num_get<charT, istreambuf_iterator<charT, traits>>; FP fval; use_facet<numget>(loc).get(*this, 0, *this, state, fval); if (fval < -numeric_limits<extended-floating-point-type>::max() { state |= ios_base::failbit; val = -numeric_limits<extended-floating-point-type>::max(); } else if (numeric_limits<extended-floating-point-type>::max() < fval) { state |= ios_base::failbit; val = numeric_limits<extended-floating-point-type>::max(); } else { val = static_cast<extended-floating-point-type>(fval); }
[Note 2: 
When the extended floating-point type has a floating-point conversion rank that is not equal to the rank of any standard floating-point type, then double rounding during the conversion can result in inaccurate results.
from_chars can be used in situations where maximum accuracy is important.
— end note]

31.7.5.3.3 basic_istream​::​operator>> [istream.extractors]

🔗
basic_istream& operator>(basic_istream& (*pf)(basic_istream&);
1
#
Effects: None.
This extractor does not behave as a formatted input function (as described in [istream.formatted.reqmts]).
2
#
Returns: pf(*this).
266
🔗
basic_istream& operator>(basic_ios<charT, traits>& (*pf)(basic_ios<charT, traits>&);
3
#
Effects: Calls pf(*this).
This extractor does not behave as a formatted input function (as described in [istream.formatted.reqmts]).
4
#
Returns: *this.
🔗
basic_istream& operator>(ios_base& (*pf)(ios_base&);
5
#
Effects: Calls pf(*this).267
This extractor does not behave as a formatted input function (as described in [istream.formatted.reqmts]).
6
#
Returns: *this.
🔗
template<class charT, class traits, size_t N> basic_istream<charT, traits>& operator>(basic_istream<charT, traits>& in, charT (&s)[N]); template<class traits, size_t N> basic_istream<char, traits>& operator>(basic_istream<char, traits>& in, unsigned char (&s)[N]); template<class traits, size_t N> basic_istream<char, traits>& operator>(basic_istream<char, traits>& in, signed char (&s)[N]);
7
#
Effects: Behaves like a formatted input member (as described in [istream.formatted.reqmts]) of in.
After a sentry object is constructed, operator> extracts characters and stores them into s.
If width() is greater than zero, n is min(size_t(width(), N).
Otherwise n is N.
n is the maximum number of characters stored.
8
#
Characters are extracted and stored until any of the following occurs:
  • (8.1)
    n - 1 characters are stored;
  • (8.2)
    end of file occurs on the input sequence;
  • (8.3)
    letting ct be use_facet<ctype<charT>>(in.getloc(), ct.is(ct.space, c) is true.
9
#
operator> then stores a null byte (charT()) in the next position, which may be the first position if no characters were extracted.
operator> then calls width(0).
10
#
If the function extracted no characters, ios_base​::​failbit is set in the input function's local error state before setstate is called.
11
#
Returns: in.
🔗
template<class charT, class traits> basic_istream<charT, traits>& operator>(basic_istream<charT, traits>& in, charT& c); template<class traits> basic_istream<char, traits>& operator>(basic_istream<char, traits>& in, unsigned char& c); template<class traits> basic_istream<char, traits>& operator>(basic_istream<char, traits>& in, signed char& c);
12
#
Effects: Behaves like a formatted input member (as described in [istream.formatted.reqmts]) of in.
A character is extracted from in, if one is available, and stored in c.
Otherwise, ios_base​::​failbit is set in the input function's local error state before setstate is called.
13
#
Returns: in.
🔗
basic_istream& operator>(basic_streambuf<charT, traits>* sb);
14
#
Effects: Behaves as an unformatted input function.
If sb is null, calls setstate(failbit), which may throw ios_base​::​failure ([iostate.flags]).
After a sentry object is constructed, extracts characters from *this and inserts them in the output sequence controlled by sb.
Characters are extracted and inserted until any of the following occurs:
  • (14.1)
    end-of-file occurs on the input sequence;
  • (14.2)
    inserting in the output sequence fails (in which case the character to be inserted is not extracted);
  • (14.3)
    an exception occurs (in which case the exception is caught).
15
#
If the function inserts no characters, ios_base​::​failbit is set in the input function's local error state before setstate is called.
16
#
Returns: *this.
266)266)
See, for example, the function signature ws(basic_istream&) ([istream.manip]).
267)267)
See, for example, the function signature dec(ios_base&) ([basefield.manip]).

31.7.5.4 Unformatted input functions [istream.unformatted]

1
#
Each unformatted input function begins execution by constructing an object of type ios_base​::​iostate, termed the local error state, and initializing it to ios_base​::​goodbit.
It then creates an object of class sentry with the default argument noskipws (second) argument true.
If the sentry object returns true, when converted to a value of type bool, the function endeavors to obtain the requested input.
Otherwise, if the sentry constructor exits by throwing an exception or if the sentry object produces false, when converted to a value of type bool, the function returns without attempting to obtain any input.
In either case the number of extracted characters is set to 0; unformatted input functions taking a character array of nonzero size as an argument shall also store a null character (using charT()) in the first location of the array.
If rdbuf()->sbumpc() or rdbuf()->sgetc() returns traits​::​eof(), then ios_base​::​eofbit is set in the local error state and the input function stops trying to obtain the requested input.
If an exception is thrown during input then ios_base​::​badbit is set in the local error state, *this's error state is set to the local error state, and the exception is rethrown if (exceptions() & badbit) != 0.
If no exception has been thrown it stores the number of characters extracted in a member object.
After extraction is done, the input function calls setstate, which sets *this's error state to the local error state, and may throw an exception.
In any event the sentry object is destroyed before leaving the unformatted input function.
🔗
streamsize gcount() const;
2
#
Effects: None.
This member function does not behave as an unformatted input function (as described above).
3
#
Returns: The number of characters extracted by the last unformatted input member function called for the object.
If the number cannot be represented, returns numeric_limits<streamsize>​::​max().
🔗
int_type get();
4
#
Effects: Behaves as an unformatted input function (as described above).
After constructing a sentry object, extracts a character c, if one is available.
Otherwise, ios_base​::​failbit is set in the input function's local error state before setstate is called.
5
#
Returns: c if available, otherwise traits​::​eof().
🔗
basic_istream& get(char_type& c);
6
#
Effects: Behaves as an unformatted input function (as described above).
After constructing a sentry object, extracts a character, if one is available, and assigns it to c.268
Otherwise, ios_base​::​failbit is set in the input function's local error state before setstate is called.
7
#
Returns: *this.
🔗
basic_istream& get(char_type* s, streamsize n, char_type delim);
8
#
Effects: Behaves as an unformatted input function (as described above).
After constructing a sentry object, extracts characters and stores them into successive locations of an array whose first element is designated by s.269
Characters are extracted and stored until any of the following occurs:
  • (8.1)
    n is less than one or n - 1 characters are stored;
  • (8.2)
    end-of-file occurs on the input sequence;
  • (8.3)
    traits​::​eq(c, delim) for the next available input character c (in which case c is not extracted).
9
#
If the function stores no characters, ios_base​::​failbit is set in the input function's local error state before setstate is called.
In any case, if n is greater than zero it then stores a null character into the next successive location of the array.
10
#
Returns: *this.
🔗
basic_istream& get(char_type* s, streamsize n);
11
#
Effects: Calls get(s, n, widen('\n').
12
#
Returns: Value returned by the call.
🔗
basic_istream& get(basic_streambuf<char_type, traits>& sb, char_type delim);
13
#
Effects: Behaves as an unformatted input function (as described above).
After constructing a sentry object, extracts characters and inserts them in the output sequence controlled by sb.
Characters are extracted and inserted until any of the following occurs:
  • (13.1)
    end-of-file occurs on the input sequence;
  • (13.2)
    inserting in the output sequence fails (in which case the character to be inserted is not extracted);
  • (13.3)
    traits​::​eq(c, delim) for the next available input character c (in which case c is not extracted);
  • (13.4)
    an exception occurs (in which case, the exception is caught but not rethrown).
14
#
If the function inserts no characters, ios_base​::​failbit is set in the input function's local error state before setstate is called.
15
#
Returns: *this.
🔗
basic_istream& get(basic_streambuf<char_type, traits>& sb);
16
#
Effects: Calls get(sb, widen('\n').
17
#
Returns: Value returned by the call.
🔗
basic_istream& getline(char_type* s, streamsize n, char_type delim);
18
#
Effects: Behaves as an unformatted input function (as described above).
After constructing a sentry object, extracts characters and stores them into successive locations of an array whose first element is designated by s.270
Characters are extracted and stored until one of the following occurs:
1.end-of-file occurs on the input sequence;
2.traits​::​eq(c, delim) for the next available input character c (in which case the input character is extracted but not stored);271
3.n is less than one or n - 1 characters are stored (in which case the function calls setstate(​failbit)).
19
#
If the function extracts no characters, ios_base​::​failbit is set in the input function's local error state before setstate is called.273
21
#
In any case, if n is greater than zero, it then stores a null character (using charT()) into the next successive location of the array.
22
#
[Example 1: #include <iostream> int main() { using namespace std; const int line_buffer_size = 100; char buffer[line_buffer_size]; int line_number = 0; while (cin.getline(buffer, line_buffer_size, '\n') || cin.gcount() { int count = cin.gcount(); if (cin.eof() cout << "Partial final line"; / cin.fail() is false else if (cin.fail() { cout << "Partial long line"; cin.clear(cin.rdstate() & ~ios_base::failbit); } else { count--; / Don't include newline in count cout << "Line " << ++line_number; } cout << " (" << count << " chars): " << buffer << endl; } } — end example]
🔗
basic_istream& getline(char_type* s, streamsize n);
24
#
Returns: getline(s, n, widen('\n').
🔗
basic_istream& ignore(streamsize n = 1, int_type delim = traits::eof();
25
#
Effects: Behaves as an unformatted input function (as described above).
After constructing a sentry object, extracts characters and discards them.
Characters are extracted until any of the following occurs:
  • (25.1)
    n != numeric_limits<streamsize>​::​max()numeric.limits and n characters have been extracted so far;
  • (25.2)
    end-of-file occurs on the input sequence (in which case the function calls setstate(eofbit), which may throw ios_base​::​failure ([iostate.flags]));
  • (25.3)
    traits​::​eq_int_type(traits​::​to_int_type(c), delim) for the next available input character c (in which case c is extracted).
[Note 1: 
The last condition will never occur if traits​::​eq_int_type(delim, traits​::​eof().
— end note]
26
#
Returns: *this.
🔗
basic_istream& ignore(streamsize n, char_type delim);
27
#
Effects: Equivalent to: return ignore(n, traits​::​to_int_type(delim));
🔗
int_type peek();
29
#
Effects: Behaves as an unformatted input function (as described above).
After constructing a sentry object, reads but does not extract the current input character.
30
#
Returns: traits​::​eof() if good() is false.
Otherwise, returns rdbuf()->sgetc().
🔗
basic_istream& read(char_type* s, streamsize n);
31
#
Effects: Behaves as an unformatted input function (as described above).
After constructing a sentry object, if !good() calls setstate(failbit) which may throw an exception, and return.
Otherwise extracts characters and stores them into successive locations of an array whose first element is designated by s.274
Characters are extracted and stored until either of the following occurs:
  • (31.1)
    n characters are stored;
  • (31.2)
    end-of-file occurs on the input sequence (in which case the function calls setstate(failbit | eofbit), which may throw ios_base​::​failure ([iostate.flags])).
32
#
Returns: *this.
🔗
streamsize readsome(char_type* s, streamsize n);
33
#
Effects: Behaves as an unformatted input function (as described above).
After constructing a sentry object, if !good() calls setstate(failbit) which may throw an exception, and return.
Otherwise extracts characters and stores them into successive locations of an array whose first element is designated by s.
If rdbuf()->in_avail() == -1, calls setstate(eofbit) (which may throw ios_base​::​failure ([iostate.flags])), and extracts no characters;
  • (33.1)
    If rdbuf()->in_avail() == 0, extracts no characters
  • (33.2)
    If rdbuf()->in_avail() > 0, extracts min(rdbuf()->in_avail(), n)).
34
#
Returns: The number of characters extracted.
🔗
basic_istream& putback(char_type c);
35
#
Effects: Behaves as an unformatted input function (as described above), except that the function first clears eofbit.
After constructing a sentry object, if !good() calls setstate(failbit) which may throw an exception, and return.
If rdbuf() is not null, calls rdbuf()->sputbackc(c).
If rdbuf() is null, or if sputbackc returns traits​::​eof(), calls setstate(badbit) (which may throw ios_base​::​failure ([iostate.flags])).
[Note 2: 
This function extracts no characters, so the value returned by the next call to gcount() is 0.
— end note]
36
#
Returns: *this.
🔗
basic_istream& unget();
37
#
Effects: Behaves as an unformatted input function (as described above), except that the function first clears eofbit.
After constructing a sentry object, if !good() calls setstate(failbit) which may throw an exception, and return.
If rdbuf() is not null, calls rdbuf()->sungetc().
If rdbuf() is null, or if sungetc returns traits​::​eof(), calls setstate(badbit) (which may throw ios_base​::​failure ([iostate.flags])).
[Note 3: 
This function extracts no characters, so the value returned by the next call to gcount() is 0.
— end note]
38
#
Returns: *this.
🔗
int sync();
39
#
Effects: Behaves as an unformatted input function (as described above), except that it does not count the number of characters extracted and does not affect the value returned by subsequent calls to gcount().
After constructing a sentry object, if rdbuf() is a null pointer, returns -1.
Otherwise, calls rdbuf()->pubsync() and, if that function returns -1 calls setstate(badbit) (which may throw ios_base​::​failure ([iostate.flags]), and returns -1.
Otherwise, returns zero.
🔗
pos_type tellg();
40
#
Effects: Behaves as an unformatted input function (as described above), except that it does not count the number of characters extracted and does not affect the value returned by subsequent calls to gcount().
41
#
Returns: After constructing a sentry object, if fail() != false, returns pos_type(-1) to indicate failure.
Otherwise, returns rdbuf()->pubseekoff(0, cur, in).
🔗
basic_istream& seekg(pos_type pos);
42
#
Effects: Behaves as an unformatted input function (as described above), except that the function first clears eofbit, it does not count the number of characters extracted, and it does not affect the value returned by subsequent calls to gcount().
After constructing a sentry object, if fail() != true, executes rdbuf()->pubseekpos(pos, ios_base​::​in).
In case of failure, the function calls setstate(failbit) (which may throw ios_base​::​failure).
43
#
Returns: *this.
🔗
basic_istream& seekg(off_type off, ios_base::seekdir dir);
44
#
Effects: Behaves as an unformatted input function (as described above), except that the function first clears eofbit, does not count the number of characters extracted, and does not affect the value returned by subsequent calls to gcount().
After constructing a sentry object, if fail() != true, executes rdbuf()->pubseekoff(off, dir, ios_base​::​in).
In case of failure, the function calls setstate(​failbit) (which may throw ios_base​::​failure).
45
#
Returns: *this.
268)268)
Note that this function is not overloaded on types signed char and unsigned char.
269)269)
Note that this function is not overloaded on types signed char and unsigned char.
270)270)
Note that this function is not overloaded on types signed char and unsigned char.
271)271)
Since the final input character is “extracted”, it is counted in the gcount(), even though it is not stored.
272)272)
This allows an input line which exactly fills the buffer, without setting failbit.
This is different behavior than the historical AT&T implementation.
273)273)
This implies an empty input line will not cause failbit to be set.
274)274)
Note that this function is not overloaded on types signed char and unsigned char.

31.7.5.5 Standard basic_istream manipulators [istream.manip]

1
#
Each instantiation of the function template specified in this subclause is a designated addressable function ([namespace.std]).
🔗
template<class charT, class traits> basic_istream<charT, traits>& ws(basic_istream<charT, traits>& is);
2
#
Effects: Behaves as an unformatted input function, except that it does not count the number of characters extracted and does not affect the value returned by subsequent calls to is.gcount().
After constructing a sentry object extracts characters as long as the next available character c is whitespace or until there are no more characters in the sequence.
Whitespace characters are distinguished with the same criterion as used by sentry​::​sentry.
If ws stops extracting characters because there are no more available it sets eofbit, but not failbit.
3
#
Returns: is.

31.7.5.6 Rvalue stream extraction [istream.rvalue]

🔗
template<class Istream, class T> Istream&& operator>(Istream&& is, T&& x);
1
#
Constraints: The expression is >> std​::​forward<T>(x) is well-formed when treated as an unevaluated operand and Istream is publicly and unambiguously derived from ios_base.
2
#
Effects: Equivalent to: is >> std::forward<T>(x); return std::move(is);

31.7.5.7 Class template basic_iostream [iostreamclass]

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namespace std { template<class charT, class traits = char_traits<charT>> class basic_iostream : public basic_istream<charT, traits>, public basic_ostream<charT, traits> { public: using char_type = charT; using int_type = traits::int_type; using pos_type = traits::pos_type; using off_type = traits::off_type; using traits_type = traits; / [iostream.cons], constructor explicit basic_iostream(basic_streambuf<charT, traits>* sb); / [iostream.dest], destructor virtual ~basic_iostream(); protected: / [iostream.cons], constructor basic_iostream(const basic_iostream&) = delete; basic_iostream(basic_iostream&& rhs); / [iostream.assign], assignment and swap basic_iostream& operator=(const basic_iostream&) = delete; basic_iostream& operator=(basic_iostream&& rhs); void swap(basic_iostream& rhs); }; }
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The class template basic_iostream inherits a number of functions that allow reading input and writing output to sequences controlled by a stream buffer.
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explicit basic_iostream(basic_streambuf<charT, traits>* sb);
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Effects: Initializes the base class subobjects with basic_istream<charT, traits>(sb) ([istream]) and basic_ostream<charT, traits>(sb).
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Postconditions: rdbuf() == sb and gcount() == 0.
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basic_iostream(basic_iostream&& rhs);
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Effects: Move constructs from the rvalue rhs by constructing the basic_istream base class with std​::​move(rhs).
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virtual ~basic_iostream();
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Remarks: Does not perform any operations on rdbuf().

31.7.5.7.4 Assignment and swap [iostream.assign]

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basic_iostream& operator=(basic_iostream&& rhs);
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Effects: Equivalent to swap(rhs).
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void swap(basic_iostream& rhs);
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The header <ostream> defines a class template and several function templates that control output to a stream buffer, along with a function template that inserts into stream rvalues.

31.7.6.2 Class template basic_ostream [ostream]

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When a function has a parameter type extended-floating-point-type, the implementation provides overloads for all cv-unqualified extended floating-point types ([basic.fundamental]).
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namespace std { template<class charT, class traits = char_traits<charT>> class basic_ostream : virtual public basic_ios<charT, traits> { public: / types (inherited from basic_ios) using char_type = charT; using int_type = traits::int_type; using pos_type = traits::pos_type; using off_type = traits::off_type; using traits_type = traits; / [ostream.cons], constructor/destructor explicit basic_ostream(basic_streambuf<char_type, traits>* sb); virtual ~basic_ostream(); / [ostream.sentry], prefix/suffix class sentry; / [ostream.formatted], formatted output basic_ostream& operator<(basic_ostream& (*pf)(basic_ostream&); basic_ostream& operator<(basic_ios<charT, traits>& (*pf)(basic_ios<charT, traits>&); basic_ostream& operator<(ios_base& (*pf)(ios_base&); basic_ostream& operator<(bool n); basic_ostream& operator<(short n); basic_ostream& operator<(unsigned short n); basic_ostream& operator<(int n); basic_ostream& operator<(unsigned int n); basic_ostream& operator<(long n); basic_ostream& operator<(unsigned long n); basic_ostream& operator<(long long n); basic_ostream& operator<(unsigned long n); basic_ostream& operator<(float f); basic_ostream& operator<(double f); basic_ostream& operator<(long double f); basic_ostream& operator<(extended-floating-point-type f); basic_ostream& operator<(const void* p); basic_ostream& operator<(const volatile void* p); basic_ostream& operator<(nullptr_t); basic_ostream& operator<(basic_streambuf<char_type, traits>* sb); / [ostream.unformatted], unformatted output basic_ostream& put(char_type c); basic_ostream& write(const char_type* s, streamsize n); basic_ostream& flush(); / [ostream.seeks], seeks pos_type tellp(); basic_ostream& seekp(pos_type); basic_ostream& seekp(off_type, ios_base::seekdir); protected: / [ostream.cons], copy/move constructor basic_ostream(const basic_ostream&) = delete; basic_ostream(basic_ostream&& rhs); / [ostream.assign], assignment and swap basic_ostream& operator=(const basic_ostream&) = delete; basic_ostream& operator=(basic_ostream&& rhs); void swap(basic_ostream& rhs); }; / [ostream.inserters.character], character inserters template<class charT, class traits> basic_ostream<charT, traits>& operator<(basic_ostream<charT, traits>&, charT); template<class charT, class traits> basic_ostream<charT, traits>& operator<(basic_ostream<charT, traits>&, char); template<class traits> basic_ostream<char, traits>& operator<(basic_ostream<char, traits>&, char); template<class traits> basic_ostream<char, traits>& operator<(basic_ostream<char, traits>&, signed char); template<class traits> basic_ostream<char, traits>& operator<(basic_ostream<char, traits>&, unsigned char); template<class traits> basic_ostream<char, traits>& operator<(basic_ostream<char, traits>&, wchar_t) = delete; template<class traits> basic_ostream<char, traits>& operator<(basic_ostream<char, traits>&, char8_t) = delete; template<class traits> basic_ostream<char, traits>& operator<(basic_ostream<char, traits>&, char16_t) = delete; template<class traits> basic_ostream<char, traits>& operator<(basic_ostream<char, traits>&, char32_t) = delete; template<class traits> basic_ostream<wchar_t, traits>& operator<(basic_ostream<wchar_t, traits>&, char8_t) = delete; template<class traits> basic_ostream<wchar_t, traits>& operator<(basic_ostream<wchar_t, traits>&, char16_t) = delete; template<class traits> basic_ostream<wchar_t, traits>& operator<(basic_ostream<wchar_t, traits>&, char32_t) = delete; template<class charT, class traits> basic_ostream<charT, traits>& operator<(basic_ostream<charT, traits>&, const charT*); template<class charT, class traits> basic_ostream<charT, traits>& operator<(basic_ostream<charT, traits>&, const char*); template<class traits> basic_ostream<char, traits>& operator<(basic_ostream<char, traits>&, const char*); template<class traits> basic_ostream<char, traits>& operator<(basic_ostream<char, traits>&, const signed char*); template<class traits> basic_ostream<char, traits>& operator<(basic_ostream<char, traits>&, const unsigned char*); template<class traits> basic_ostream<char, traits>& operator<(basic_ostream<char, traits>&, const wchar_t*) = delete; template<class traits> basic_ostream<char, traits>& operator<(basic_ostream<char, traits>&, const char8_t*) = delete; template<class traits> basic_ostream<char, traits>& operator<(basic_ostream<char, traits>&, const char16_t*) = delete; template<class traits> basic_ostream<char, traits>& operator<(basic_ostream<char, traits>&, const char32_t*) = delete; template<class traits> basic_ostream<wchar_t, traits>& operator<(basic_ostream<wchar_t, traits>&, const char8_t*) = delete; template<class traits> basic_ostream<wchar_t, traits>& operator<(basic_ostream<wchar_t, traits>&, const char16_t*) = delete; template<class traits> basic_ostream<wchar_t, traits>& operator<(basic_ostream<wchar_t, traits>&, const char32_t*) = delete; }
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The class template basic_ostream defines a number of member function signatures that assist in formatting and writing output to output sequences controlled by a stream buffer.
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Two groups of member function signatures share common properties: the formatted output functions (or inserters) and the unformatted output functions. Both groups of output functions generate (or insert) output characters by actions equivalent to calling rdbuf()->sputc(int_type).
They may use other public members of basic_ostream except that they shall not invoke any virtual members of rdbuf() except overflow(), xsputn(), and sync().
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If one of these called functions throws an exception, then unless explicitly noted otherwise the output function sets badbit in the error state.
If badbit is set in exceptions(), the output function rethrows the exception without completing its actions, otherwise it does not throw anything and proceeds as if the called function had returned a failure indication.
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[Note 1: 
The deleted overloads of operator< prevent formatting characters as integers and strings as pointers.
— end note]
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explicit basic_ostream(basic_streambuf<charT, traits>* sb);
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Effects: Initializes the base class subobject with basic_ios<charT, traits>​::​init(sb) ([basic.ios.cons]).
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Postconditions: rdbuf() == sb.
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basic_ostream(basic_ostream&& rhs);
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Effects: Move constructs from the rvalue rhs.
This is accomplished by default constructing the base class and calling basic_ios<charT, traits>​::​move(rhs) to initialize the base class.
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virtual ~basic_ostream();
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Remarks: Does not perform any operations on rdbuf().

31.7.6.2.3 Assignment and swap [ostream.assign]

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basic_ostream& operator=(basic_ostream&& rhs);
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Returns: *this.
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void swap(basic_ostream& rhs);
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Effects: Calls basic_ios<charT, traits>​::​swap(rhs).

31.7.6.2.4 Class basic_ostream​::​sentry [ostream.sentry]

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namespace std { template<class charT, class traits> class basic_ostream<charT, traits>::sentry { bool ok_; / exposition only public: explicit sentry(basic_ostream& os); ~sentry(); explicit operator bool() const { return ok_; } sentry(const sentry&) = delete; sentry& operator=(const sentry&) = delete; }; }
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The class sentry defines a class that is responsible for doing exception safe prefix and suffix operations.
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explicit sentry(basic_ostream& os);
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If os.good() is nonzero, prepares for formatted or unformatted output.
If os.tie() is not a null pointer, calls os.tie()->flush().275
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If, after any preparation is completed, os.good() is true, ok_ == true otherwise, ok_ == false.
During preparation, the constructor may call setstate(failbit) (which may throw ios_base​::​​failure ([iostate.flags])).276
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~sentry();
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If (os.flags() & ios_base​::​unitbuf) && !uncaught_exceptions() && os.good() is true, calls os.rdbuf()->pubsync().
If that function returns
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explicit operator bool() const;
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Effects: Returns ok_.
275)275)
The call os.tie()->flush() does not necessarily occur if the function can determine that no synchronization is necessary.
276)276)
The sentry constructor and destructor can also perform additional implementation-dependent operations.
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Each seek member function begins execution by constructing an object of class sentry.
It returns by destroying the sentry object.
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pos_type tellp();
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Returns: If fail() != false, returns pos_type(-1) to indicate failure.
Otherwise, returns rdbuf()->​pubseekoff(​0, cur, out).
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basic_ostream& seekp(pos_type pos);
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Effects: If fail() != true, executes rdbuf()->pubseekpos(pos, ios_base​::​out).
In case of failure, the function calls setstate(failbit) (which may throw ios_base​::​failure).
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Returns: *this.
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basic_ostream& seekp(off_type off, ios_base::seekdir dir);
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Effects: If fail() != true, executes rdbuf()->pubseekoff(off, dir, ios_base​::​out).
In case of failure, the function calls setstate(failbit) (which may throw ios_base​::​failure).
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Each formatted output function begins execution by constructing an object of class sentry.
If that object returns true when converted to a value of type bool, the function endeavors to generate the requested output.
If the generation fails, then the formatted output function does setstate(ios_base​::​failbit), which can throw an exception.
If an exception is thrown during output, then ios_base​::​badbit is set277 in *this's error state.
If (exceptions() & badbit) != 0 then the exception is rethrown.
Whether or not an exception is thrown, the sentry object is destroyed before leaving the formatted output function.
If no exception is thrown, the result of the formatted output function is *this.
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The descriptions of the individual formatted output functions describe how they perform output and do not mention the sentry object.
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If a formatted output function of a stream os determines padding, it does so as follows.
Given a charT character sequence seq where charT is the character container type of the stream, if the length of seq is less than os.width(), then enough copies of os.fill() are added to this sequence as necessary to pad to a width of os.width() characters.
If (os.flags() & ios_base​::​adjustfield) == ios_base​::​left is true, the fill characters are placed after the character sequence; otherwise, they are placed before the character sequence.
277)277)
This is done without causing an ios_base​::​failure to be thrown.
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basic_ostream& operator<(bool val); basic_ostream& operator<(short val); basic_ostream& operator<(unsigned short val); basic_ostream& operator<(int val); basic_ostream& operator<(unsigned int val); basic_ostream& operator<(long val); basic_ostream& operator<(unsigned long val); basic_ostream& operator<(long long val); basic_ostream& operator<(unsigned long val); basic_ostream& operator<(float val); basic_ostream& operator<(double val); basic_ostream& operator<(long double val); basic_ostream& operator<(const void* val);
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Effects: The classes num_get<> and num_put<> handle locale-dependent numeric formatting and parsing.
These inserter functions use the imbued locale value to perform numeric formatting.
When val is of type bool, long, unsigned long, long long, unsigned long, double, long double, or const void*, the formatting conversion occurs as if it performed the following code fragment: bool failed = use_facet<num_put<charT, ostreambuf_iterator<charT, traits>>( getloc().put(*this, *this, fill(), val).failed();
When val is of type short the formatting conversion occurs as if it performed the following code fragment: ios_base::fmtflags baseflags = ios_base::flags() & ios_base::basefield; bool failed = use_facet<num_put<charT, ostreambuf_iterator<charT, traits>>( getloc().put(*this, *this, fill(), baseflags == ios_base::oct || baseflags == ios_base::hex ? static_cast<long>(static_cast<unsigned short>(val)) : static_cast<long>(val)).failed();
When val is of type int the formatting conversion occurs as if it performed the following code fragment: ios_base::fmtflags baseflags = ios_base::flags() & ios_base::basefield; bool failed = use_facet<num_put<charT, ostreambuf_iterator<charT, traits>>( getloc().put(*this, *this, fill(), baseflags == ios_base::oct || baseflags == ios_base::hex ? static_cast<long>(static_cast<unsigned int>(val)) : static_cast<long>(val)).failed();
When val is of type unsigned short or unsigned int the formatting conversion occurs as if it performed the following code fragment: bool failed = use_facet<num_put<charT, ostreambuf_iterator<charT, traits>>( getloc().put(*this, *this, fill(), static_cast<unsigned long>(val)).failed();
When val is of type float the formatting conversion occurs as if it performed the following code fragment: bool failed = use_facet<num_put<charT, ostreambuf_iterator<charT, traits>>( getloc().put(*this, *this, fill(), static_cast<double>(val)).failed();
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The first argument provides an object of the ostreambuf_iterator<> class which is an iterator for class basic_ostream<>.
It bypasses ostreams and uses streambufs directly.
Class locale relies on these types as its interface to iostreams, since for flexibility it has been abstracted away from direct dependence on ostream.
The second parameter is a reference to the base class subobject of type ios_base.
It provides formatting specifications such as field width, and a locale from which to obtain other facets.
If failed is true then does setstate(badbit), which may throw an exception, and returns.
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Returns: *this.
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basic_ostream& operator<(const volatile void* p);
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Effects: Equivalent to: return operator<(const_cast<const void*>(p));
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basic_ostream& operator<(extended-floating-point-type val);
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Effects: If the floating-point conversion rank of extended-floating-point-type is less than or equal to that of double, the formatting conversion occurs as if it performed the following code fragment: bool failed = use_facet<num_put<charT, ostreambuf_iterator<charT, traits>>( getloc().put(*this, *this, fill(), static_cast<double>(val)).failed();
Otherwise, if the floating-point conversion rank of extended-floating-point-type is less than or equal to that of long double, the formatting conversion occurs as if it performed the following code fragment: bool failed = use_facet<num_put<charT, ostreambuf_iterator<charT, traits>>( getloc().put(*this, *this, fill(), static_cast<long double>(val)).failed();
Otherwise, an invocation of the operator function is conditionally supported with implementation-defined semantics.
If failed is true then does setstate(badbit), which may throw an exception, and returns.
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Returns: *this.

31.7.6.3.3 basic_ostream​::​operator<< [ostream.inserters]

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basic_ostream& operator<(basic_ostream& (*pf)(basic_ostream&);
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Effects: None.
Does not behave as a formatted output function (as described in [ostream.formatted.reqmts]).
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Returns: pf(*this).278
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basic_ostream& operator<(basic_ios<charT, traits>& (*pf)(basic_ios<charT, traits>&);
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Effects: Calls pf(*this).
This inserter does not behave as a formatted output function (as described in [ostream.formatted.reqmts]).
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Returns: *this.279
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basic_ostream& operator<(ios_base& (*pf)(ios_base&);
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Effects: Calls pf(*this).
This inserter does not behave as a formatted output function (as described in [ostream.formatted.reqmts]).
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Returns: *this.
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basic_ostream& operator<(basic_streambuf<charT, traits>* sb);
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Effects: Behaves as an unformatted output function ([ostream.unformatted]).
After the sentry object is constructed, if sb is null calls setstate(badbit) (which may throw ios_base​::​failure).
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Gets characters from sb and inserts them in *this.
Characters are read from sb and inserted until any of the following occurs:
  • (8.1)
    end-of-file occurs on the input sequence;
  • (8.2)
    inserting in the output sequence fails (in which case the character to be inserted is not extracted);
  • (8.3)
    an exception occurs while getting a character from sb.
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If the function inserts no characters, it calls setstate(failbit) (which may throw ios_base​::​​failure ([iostate.flags])).
If an exception was thrown while extracting a character, the function sets failbit in the error state, and if failbit is set in exceptions() the caught exception is rethrown.
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Returns: *this.
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basic_ostream& operator<(nullptr_t);
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Effects: Equivalent to: return *this << s; where s is an implementation-defined NTCTS.
278)278)
See, for example, the function signature endl(basic_ostream&) ([ostream.manip]).
279)279)
See, for example, the function signature dec(ios_base&) ([basefield.manip]).

31.7.6.3.4 Character inserter function templates [ostream.inserters.character]

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template<class charT, class traits> basic_ostream<charT, traits>& operator<(basic_ostream<charT, traits>& out, charT c); template<class charT, class traits> basic_ostream<charT, traits>& operator<(basic_ostream<charT, traits>& out, char c); / specialization template<class traits> basic_ostream<char, traits>& operator<(basic_ostream<char, traits>& out, char c); / signed and unsigned template<class traits> basic_ostream<char, traits>& operator<(basic_ostream<char, traits>& out, signed char c); template<class traits> basic_ostream<char, traits>& operator<(basic_ostream<char, traits>& out, unsigned char c);
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Effects: Behaves as a formatted output function of out.
Constructs a character sequence seq.
If c has type char and the character container type of the stream is not char, then seq consists of out.widen(c); otherwise seq consists of c.
Determines padding for seq as described in [ostream.formatted.reqmts].
Inserts seq into out.
Calls os.width(0).
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Returns: out.
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template<class charT, class traits> basic_ostream<charT, traits>& operator<(basic_ostream<charT, traits>& out, const charT* s); template<class charT, class traits> basic_ostream<charT, traits>& operator<(basic_ostream<charT, traits>& out, const char* s); template<class traits> basic_ostream<char, traits>& operator<(basic_ostream<char, traits>& out, const char* s); template<class traits> basic_ostream<char, traits>& operator<(basic_ostream<char, traits>& out, const signed char* s); template<class traits> basic_ostream<char, traits>& operator<(basic_ostream<char, traits>& out, const unsigned char* s);
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Effects: Behaves like a formatted inserter (as described in [ostream.formatted.reqmts]) of out.
Creates a character sequence seq of n characters starting at s, each widened using out.widen() ([basic.ios.members]), where n is the number that would be computed as if by:
  • (4.1)
    traits​::​length(s) for the overload where the first argument is of type basic_ostream<charT, traits>& and the second is of type const charT*, and also for the overload where the first argument is of type basic_ostream<char, traits>& and the second is of type const char*,
  • (4.2)
    char_traits<char>​::​length(s) for the overload where the first argument is of type basic_ostream<charT, traits>& and the second is of type const char*,
  • (4.3)
    traits​::​length(reinterpret_cast<const char*>(s)) for the other two overloads.
Determines padding for seq as described in [ostream.formatted.reqmts].
Inserts seq into out.
Calls width(0).
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Returns: out.
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template<class. Args> void print(ostream& os, format_string<Args..> fmt, Args&&. args);
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Effects: If the ordinary literal encoding ([lex.charset]) is UTF-8, equivalent to: vprint_unicode(os, fmt.str, make_format_args(args..);
Otherwise, equivalent to: vprint_nonunicode(os, fmt.str, make_format_args(args..);
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template<class. Args> void println(ostream& os, format_string<Args..> fmt, Args&&. args);
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Effects: Equivalent to: print(os, "{}\n", format(os.getloc(), fmt, std::forward<Args>(args).);
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void println(ostream& os);
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Effects: Equivalent to: print(os, "\n");
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void vprint_unicode(ostream& os, string_view fmt, format_args args); void vprint_nonunicode(ostream& os, string_view fmt, format_args args);
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Effects: Behaves as a formatted output function ([ostream.formatted.reqmts]) of os, except that:
  • (4.1)
    failure to generate output is reported as specified below, and
  • (4.2)
    any exception thrown by the call to vformat is propagated without regard to the value of os.exceptions() and without turning on ios_base​::​badbit in the error state of os.
After constructing a sentry object, the function initializes a variable with automatic storage duration via string out = vformat(os.getloc(), fmt, args);
  • (4.3)
    If the function is vprint_unicode and os is a stream that refers to a terminal that is capable of displaying Unicode only via a native Unicode API, which is determined in an implementation-defined manner, flushes os and then writes out to the terminal using the native Unicode API; if out contains invalid code units, the behavior is undefined.
    Then establishes an observable checkpoint ([intro.abstract]).
  • (4.4)
    Otherwise inserts the character sequence [out.begin(), out.end()) into os.
If writing to the terminal or inserting into os fails, calls os.setstate(ios_base​::​badbit) (which may throw ios_base​::​failure).
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Recommended practice: For vprint_unicode, if invoking the native Unicode API requires transcoding, implementations should substitute invalid code units with U+fffd replacement character per the Unicode Standard, Chapter 3.9 U+fffd Substitution in Conversion.

31.7.6.4 Unformatted output functions [ostream.unformatted]

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Each unformatted output function begins execution by constructing an object of class sentry.
If that object returns true, while converting to a value of type bool, the function endeavors to generate the requested output.
If an exception is thrown during output, then ios_base​::​badbit is set280 in *this's error state.
If (exceptions() & badbit) != 0 then the exception is rethrown.
In any case, the unformatted output function ends by destroying the sentry object, then, if no exception was thrown, returning the value specified for the unformatted output function.
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basic_ostream& put(char_type c);
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Effects: Behaves as an unformatted output function (as described above).
After constructing a sentry object, inserts the character c, if possible.281
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Otherwise, calls setstate(badbit) (which may throw ios_base​::​failure ([iostate.flags])).
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Returns: *this.
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basic_ostream& write(const char_type* s, streamsize n);
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Effects: Behaves as an unformatted output function (as described above).
After constructing a sentry object, obtains characters to insert from successive locations of an array whose first element is designated by s.282
Characters are inserted until either of the following occurs:
  • (5.1)
    n characters are inserted;
  • (5.2)
    inserting in the output sequence fails (in which case the function calls setstate(badbit), which may throw ios_base​::​failure ([iostate.flags])).
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Returns: *this.
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basic_ostream& flush();
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Effects: Behaves as an unformatted output function (as described above).
If rdbuf() is not a null pointer, constructs a sentry object.
If that object returns true when converted to a value of type bool the function calls rdbuf()->pubsync().
If that function returns
Otherwise, if the sentry object returns false, does nothing.
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Returns: *this.
280)280)
This is done without causing an ios_base​::​failure to be thrown.
281)281)
Note that this function is not overloaded on types signed char and unsigned char.
282)282)
Note that this function is not overloaded on types signed char and unsigned char.

31.7.6.5 Standard basic_ostream manipulators [ostream.manip]

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Each instantiation of any of the function templates specified in this subclause is a designated addressable function ([namespace.std]).
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template<class charT, class traits> basic_ostream<charT, traits>& endl(basic_ostream<charT, traits>& os);
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Effects: Calls os.put(os.widen('\n'), then os.flush().
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Returns: os.
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template<class charT, class traits> basic_ostream<charT, traits>& ends(basic_ostream<charT, traits>& os);
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Effects: Inserts a null character into the output sequence: calls os.put(charT().
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Returns: os.
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template<class charT, class traits> basic_ostream<charT, traits>& flush(basic_ostream<charT, traits>& os);
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Effects: Calls os.flush().
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Returns: os.
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template<class charT, class traits> basic_ostream<charT, traits>& emit_on_flush(basic_ostream<charT, traits>& os);
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Effects: If os.rdbuf() is a basic_syncbuf<charT, traits, Allocator>*, called buf for the purpose of exposition, calls buf->set_emit_on_sync(true).
Otherwise this manipulator has no effect.
[Note 1: 
To work around the issue that the Allocator template argument cannot be deduced, implementations can introduce an intermediate base class to basic_syncbuf that manages its emit-on-sync flag.
— end note]
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Returns: os.
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template<class charT, class traits> basic_ostream<charT, traits>& noemit_on_flush(basic_ostream<charT, traits>& os);
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Effects: If os.rdbuf() is a basic_syncbuf<charT, traits, Allocator>*, called buf for the purpose of exposition, calls buf->set_emit_on_sync(false).
Otherwise this manipulator has no effect.
11
#
Returns: os.
🔗
template<class charT, class traits> basic_ostream<charT, traits>& flush_emit(basic_ostream<charT, traits>& os);
12
#
Effects: Calls os.flush().
Then, if os.rdbuf() is a basic_syncbuf<charT, traits, Allocator>*, called buf for the purpose of exposition, behaves as an unformatted output function ([ostream.unformatted]) of os.
After constructing a sentry object, calls buf->emit().
If that call returns false, calls os.setstate(ios_base​::​badbit).
13
#
Returns: os.

31.7.6.6 Rvalue stream insertion [ostream.rvalue]

🔗
template<class Ostream, class T> Ostream&& operator<(Ostream&& os, const T& x);
1
#
Constraints: The expression os << x is well-formed when treated as an unevaluated operand and Ostream is publicly and unambiguously derived from ios_base.
2
#
The header <iomanip> defines several functions that support extractors and inserters that alter information maintained by class ios_base and its derived classes.
🔗
unspecified resetiosflags(ios_base::fmtflags mask);
2
#
Returns: An object of unspecified type such that if out is an object of type basic_ostream<charT, traits> then the expression out << resetiosflags(mask) behaves as if it called f(out, mask), or if in is an object of type basic_istream<charT, traits> then the expression in >> resetiosflags(​mask) behaves as if it called f(in, mask), where the function f is defined as:283 void f(ios_base& str, ios_base::fmtflags mask) { / reset specified flags str.setf(ios_base::fmtflags(0), mask); }
The expression out << resetiosflags(mask) has type basic_ostream<charT, traits>& and value out.
The expression in >> resetiosflags(mask) has type basic_istream<charT, traits>& and value in.
🔗
unspecified setiosflags(ios_base::fmtflags mask);
3
#
Returns: An object of unspecified type such that if out is an object of type basic_ostream<charT, traits> then the expression out << setiosflags(mask) behaves as if it called f(out, mask), or if in is an object of type basic_istream<charT, traits> then the expression in >> setiosflags(mask) behaves as if it called f(in, mask), where the function f is defined as:
🔗
void f(ios_base& str, ios_base::fmtflags mask) { / set specified flags str.setf(mask); }
The expression out << setiosflags(mask) has type basic_ostream<charT, traits>& and value out.
The expression in >> setiosflags(mask) has type basic_istream<charT, traits>& and value in.
🔗
unspecified setbase(int base);
4
#
Returns: An object of unspecified type such that if out is an object of type basic_ostream<charT, traits> then the expression out << setbase(base) behaves as if it called f(out, base), or if in is an object of type basic_istream<charT, traits> then the expression in >> setbase(base) behaves as if it called f(in, base), where the function f is defined as: void f(ios_base& str, int base) { / set basefield str.setf(base == 8 ? ios_base::oct : base == 10 ? ios_base::dec : base == 16 ? ios_base::hex : ios_base::fmtflags(0), ios_base::basefield); }
The expression out << setbase(base) has type basic_ostream<charT, traits>& and value out.
The expression in >> setbase(base) has type basic_istream<charT, traits>& and value in.
🔗
unspecified setfill(char_type c);
5
#
Returns: An object of unspecified type such that if out is an object of type basic_ostream<charT, traits> and c has type charT then the expression out << setfill(c) behaves as if it called f(out, c), where the function f is defined as: template<class charT, class traits> void f(basic_ios<charT, traits>& str, charT c) { / set fill character str.fill(c); }
The expression out << setfill(c) has type basic_ostream<charT, traits>& and value out.
🔗
unspecified setprecision(int n);
6
#
Returns: An object of unspecified type such that if out is an object of type basic_ostream<charT, traits> then the expression out << setprecision(n) behaves as if it called f(out, n), or if in is an object of type basic_istream<charT, traits> then the expression in >> setprecision(n) behaves as if it called f(in, n), where the function f is defined as: void f(ios_base& str, int n) { / set precision str.precision(n); }
The expression out << setprecision(n) has type basic_ostream<charT, traits>& and value out.
The expression in >> setprecision(n) has type basic_istream<charT, traits>& and value in.
🔗
unspecified setw(int n);
7
#
Returns: An object of unspecified type such that if out is an instance of basic_ostream<charT, traits> then the expression out << setw(n) behaves as if it called f(out, n), or if in is an object of type basic_istream<charT, traits> then the expression in >> setw(n) behaves as if it called f(in, n), where the function f is defined as: void f(ios_base& str, int n) { / set width str.width(n); }
The expression out << setw(n) has type basic_ostream<charT, traits>& and value out.
The expression in >> setw(n) has type basic_istream<charT, traits>& and value in.
283)283)
The expression cin >> resetiosflags(ios_base​::​skipws) clears ios_base​::​skipws in the format flags stored in the basic_istream<charT, traits> object cin (the same as cin >> noskipws), and the expression cout << resetiosflags(ios_base​::​showbase) clears ios_base​::​showbase in the format flags stored in the basic_ostream<charT, traits> object cout (the same as cout << noshowbase).

31.7.8 Extended manipulators [ext.manip]

1
#
The header <iomanip> defines several functions that support extractors and inserters that allow for the parsing and formatting of sequences and values for money and time.
🔗
template<class moneyT> unspecified get_money(moneyT& mon, bool intl = false);
2
#
Mandates: The type moneyT is either long double or a specialization of the basic_string template ([strings]).
3
#
Effects: The expression in >> get_money(mon, intl) described below behaves as a formatted input function.
4
#
Returns: An object of unspecified type such that if in is an object of type basic_istream<charT, traits> then the expression in >> get_money(mon, intl) behaves as if it called f(in, mon, intl), where the function f is defined as: template<class charT, class traits, class moneyT> void f(basic_ios<charT, traits>& str, moneyT& mon, bool intl) { using Iter = istreambuf_iterator<charT, traits>; using MoneyGet = money_get<charT, Iter>; ios_base::iostate err = ios_base::goodbit; const MoneyGet& mg = use_facet<MoneyGet>(str.getloc(); mg.get(Iter(str.rdbuf(), Iter(), intl, str, err, mon); if (ios_base::goodbit != err) str.setstate(err); }
The expression in >> get_money(mon, intl) has type basic_istream<charT, traits>& and value in.
🔗
template<class moneyT> unspecified put_money(const moneyT& mon, bool intl = false);
5
#
Mandates: The type moneyT is either long double or a specialization of the basic_string template ([strings]).
6
#
Returns: An object of unspecified type such that if out is an object of type basic_ostream<charT, traits> then the expression out << put_money(mon, intl) behaves as a formatted output function that calls f(out, mon, intl), where the function f is defined as: template<class charT, class traits, class moneyT> void f(basic_ios<charT, traits>& str, const moneyT& mon, bool intl) { using Iter = ostreambuf_iterator<charT, traits>; using MoneyPut = money_put<charT, Iter>; const MoneyPut& mp = use_facet<MoneyPut>(str.getloc(); const Iter end = mp.put(Iter(str.rdbuf(), intl, str, str.fill(), mon); if (end.failed() str.setstate(ios_base::badbit); }
The expression out << put_money(mon, intl) has type basic_ostream<charT, traits>& and value out.
🔗
template<class charT> unspecified get_time(tm* tmb, const charT* fmt);
7
#
Preconditions: The argument tmb is a valid pointer to an object of type tm, and [fmt, fmt + char_traits<charT>​::​length(fmt)) is a valid range.
8
#
Returns: An object of unspecified type such that if in is an object of type basic_istream<charT, traits> then the expression in >> get_time(tmb, fmt) behaves as if it called f(in, tmb, fmt), where the function f is defined as: template<class charT, class traits> void f(basic_ios<charT, traits>& str, tm* tmb, const charT* fmt) { using Iter = istreambuf_iterator<charT, traits>; using TimeGet = time_get<charT, Iter>; ios_base::iostate err = ios_base::goodbit; const TimeGet& tg = use_facet<TimeGet>(str.getloc(); tg.get(Iter(str.rdbuf(), Iter(), str, err, tmb, fmt, fmt + traits::length(fmt)); if (err != ios_base::goodbit) str.setstate(err); }
The expression in >> get_time(tmb, fmt) has type basic_istream<charT, traits>& and value in.
🔗
template<class charT> unspecified put_time(const tm* tmb, const charT* fmt);
9
#
Preconditions: The argument tmb is a valid pointer to an object of type tm, and [fmt, fmt + char_traits<charT>​::​length(fmt)) is a valid range.
10
#
Returns: An object of unspecified type such that if out is an object of type basic_ostream<charT, traits> then the expression out << put_time(tmb, fmt) behaves as if it called f(out, tmb, fmt), where the function f is defined as: template<class charT, class traits> void f(basic_ios<charT, traits>& str, const tm* tmb, const charT* fmt) { using Iter = ostreambuf_iterator<charT, traits>; using TimePut = time_put<charT, Iter>; const TimePut& tp = use_facet<TimePut>(str.getloc(); const Iter end = tp.put(Iter(str.rdbuf(), str, str.fill(), tmb, fmt, fmt + traits::length(fmt)); if (end.failed() str.setstate(ios_base::badbit); }
The expression out << put_time(tmb, fmt) has type basic_ostream<charT, traits>& and value out.

31.7.9 Quoted manipulators [quoted.manip]

1
#
[Note 1: 
Quoted manipulators provide string insertion and extraction of quoted strings (for example, XML and CSV formats).
Quoted manipulators are useful in ensuring that the content of a string with embedded spaces remains unchanged if inserted and then extracted via stream I/O.
— end note]
🔗
template<class charT> unspecified quoted(const charT* s, charT delim = charT('"'), charT escape = charT('\\'); template<class charT, class traits, class Allocator> unspecified quoted(const basic_string<charT, traits, Allocator>& s, charT delim = charT('"'), charT escape = charT('\\'); template<class charT, class traits> unspecified quoted(basic_string_view<charT, traits> s, charT delim = charT('"'), charT escape = charT('\\');
2
#
Returns: An object of unspecified type such that if out is an instance of basic_ostream with member type char_type the same as charT and with member type traits_type, which in the second and third forms is the same as traits, then the expression out << quoted(s, delim, escape) behaves as a formatted output function of out.
This forms a character sequence seq, initially consisting of the following elements:
  • (2.1)
    delim.
  • (2.2)
    Each character in s.
    If the character to be output is equal to escape or delim, as determined by traits_type​::​eq, first output escape.
  • (2.3)
    delim.
Let x be the number of elements initially in seq.
Then padding is determined for seq as described in [ostream.formatted.reqmts], seq is inserted as if by calling out.rdbuf()->sputn(seq, n), where n is the larger of out.width() and x, and out.width(0) is called.
The expression out << quoted(s, delim, escape) has type basic_ostream<charT, traits>& and value out.
🔗
template<class charT, class traits, class Allocator> unspecified quoted(basic_string<charT, traits, Allocator>& s, charT delim = charT('"'), charT escape = charT('\\');
3
#
Returns: An object of unspecified type such that:
  • (3.1)
    If in is an instance of basic_istream with member types char_type and traits_type the same as charT and traits, respectively, then the expression in >> quoted(s, delim, escape) behaves as if it extracts the following characters from in using operator>(basic_istream<charT, traits>&, charT&) ([istream.extractors]) which may throw ios_base​::​failure ([ios.failure]):
    • (3.1.1)
      If the first character extracted is equal to delim, as determined by traits_type​::​eq, then:
      • (3.1.1.1)
        Turn off the skipws flag.
      • (3.1.1.2)
        s.clear()
      • (3.1.1.3)
        Until an unescaped delim character is reached or !in, extract characters from in and append them to s, except that if an escape is reached, ignore it and append the next character to s.
      • (3.1.1.4)
        Discard the final delim character.
      • (3.1.1.5)
        Restore the skipws flag to its original value.
    • (3.1.2)
      Otherwise, in >> s.
  • (3.2)
    If out is an instance of basic_ostream with member types char_type and traits_type the same as charT and traits, respectively, then the expression out << quoted(s, delim, escape) behaves as specified for the const basic_string<charT, traits, Allocator>& overload of the quoted function.
  • (3.3)
    The expression in >> quoted(s, delim, escape) has type basic_istream<charT, traits>& and value in.
  • (3.4)
    The expression out << quoted(s, delim, escape) has type basic_ostream​<charT, traits>& and value out.

31.7.10 Print functions [print.fun]

🔗
template<class. Args> void print(format_string<Args..> fmt, Args&&. args);
1
#
Effects: Equivalent to: print(stdout, fmt, std::forward<Args>(args).);
🔗
template<class. Args> void print(FILE* stream, format_string<Args..> fmt, Args&&. args);
2
#
Effects: Let locksafe be (enable_nonlocking_formatter_optimization<remove_cvref_t<Args>> && ..).
If the ordinary literal encoding ([lex.charset]) is UTF-8, equivalent to: locksafe ? vprint_unicode(stream, fmt.str, make_format_args(args..) : vprint_unicode_buffered(stream, fmt.str, make_format_args(args..);
Otherwise, equivalent to: locksafe ? vprint_nonunicode(stream, fmt.str, make_format_args(args..) : vprint_nonunicode_buffered(stream, fmt.str, make_format_args(args..);
🔗
template<class. Args> void println(format_string<Args..> fmt, Args&&. args);
3
#
Effects: Equivalent to: println(stdout, fmt, std::forward<Args>(args).);
🔗
void println();
4
#
Effects: Equivalent to: println(stdout);
🔗
template<class. Args> void println(FILE* stream, format_string<Args..> fmt, Args&&. args);
5
#
Effects: Equivalent to: print(stream, runtime_format(string(fmt.get() + '\n'), std::forward<Args>(args).);
🔗
void println(FILE* stream);
6
#
Effects: Equivalent to: print(stream, "\n");
🔗
void vprint_unicode(string_view fmt, format_args args);
7
#
Effects: Equivalent to: vprint_unicode(stdout, fmt, args);
🔗
void vprint_unicode_buffered(FILE* stream, string_view fmt, format_args args);
8
#
Effects: Equivalent to: string out = vformat(fmt, args); vprint_unicode(stream, "{}", make_format_args(out));
🔗
void vprint_unicode(FILE* stream, string_view fmt, format_args args);
9
#
Effects: Locks stream.
Let out denote the character representation of formatting arguments provided by args formatted according to specifications given in fmt.
  • (10.1)
    If stream refers to a terminal that is capable of displaying Unicode only via a native Unicode API, flushes stream and then writes out to the terminal using the native Unicode API; if out contains invalid code units, the behavior is undefined.
    Then establishes an observable checkpoint ([intro.abstract]).
  • (10.2)
    Otherwise writes out to stream unchanged.
Unconditionally unlocks stream on function exit.
See also: ISO/IEC 9899:2024, 7.23.2.
[Note 1: 
On Windows the native Unicode API is WriteConsoleW and stream referring to a terminal means that GetConsoleMode(_get_osfhandle(_fileno(stream)), ..) returns nonzero.
— end note]
11
#
Recommended practice: If invoking the native Unicode API requires transcoding, implementations should substitute invalid code units with U+fffd replacement character per the Unicode Standard, Chapter 3.9 U+fffd Substitution in Conversion.
🔗
void vprint_nonunicode(string_view fmt, format_args args);
13
#
Effects: Equivalent to: vprint_nonunicode(stdout, fmt, args);
🔗
void vprint_nonunicode_buffered(FILE* stream, string_view fmt, format_args args);
14
#
Effects: Equivalent to: string out = vformat(fmt, args); vprint_nonunicode("{}", make_format_args(out));
🔗
void vprint_nonunicode(FILE* stream, string_view fmt, format_args args);
15
#
Effects: While holding the lock on stream, writes the character representation of formatting arguments provided by args formatted according to specifications given in fmt to stream.
17
#
Throws: Any exception thrown by the call to vformat ([format.err.report]).
system_error if writing to stream fails.
May throw bad_alloc.

31.8 String-based streams [string.streams]

31.8.1 Header <sstream> synopsis [sstream.syn]

🔗
namespace std { / [stringbuf], class template basic_stringbuf template<class charT, class traits = char_traits<charT>, class Allocator = allocator<charT>> class basic_stringbuf; template<class charT, class traits, class Allocator> void swap(basic_stringbuf<charT, traits, Allocator>& x, basic_stringbuf<charT, traits, Allocator>& y) noexcept(noexcept(x.swap(y)); using stringbuf = basic_stringbuf<char>; using wstringbuf = basic_stringbuf<wchar_t>; / [istringstream], class template basic_istringstream template<class charT, class traits = char_traits<charT>, class Allocator = allocator<charT>> class basic_istringstream; template<class charT, class traits, class Allocator> void swap(basic_istringstream<charT, traits, Allocator>& x, basic_istringstream<charT, traits, Allocator>& y); using istringstream = basic_istringstream<char>; using wistringstream = basic_istringstream<wchar_t>; / [ostringstream], class template basic_ostringstream template<class charT, class traits = char_traits<charT>, class Allocator = allocator<charT>> class basic_ostringstream; template<class charT, class traits, class Allocator> void swap(basic_ostringstream<charT, traits, Allocator>& x, basic_ostringstream<charT, traits, Allocator>& y); using ostringstream = basic_ostringstream<char>; using wostringstream = basic_ostringstream<wchar_t>; / [stringstream], class template basic_stringstream template<class charT, class traits = char_traits<charT>, class Allocator = allocator<charT>> class basic_stringstream; template<class charT, class traits, class Allocator> void swap(basic_stringstream<charT, traits, Allocator>& x, basic_stringstream<charT, traits, Allocator>& y); using stringstream = basic_stringstream<char>; using wstringstream = basic_stringstream<wchar_t>; }
1
#
The header <sstream> defines four class templates and eight types that associate stream buffers with objects of class basic_string, as described in [string.classes].

31.8.2 Class template basic_stringbuf [stringbuf]

🔗
namespace std { template<class charT, class traits = char_traits<charT>, class Allocator = allocator<charT>> class basic_stringbuf : public basic_streambuf<charT, traits> { public: using char_type = charT; using int_type = traits::int_type; using pos_type = traits::pos_type; using off_type = traits::off_type; using traits_type = traits; using allocator_type = Allocator; / [stringbuf.cons], constructors basic_stringbuf() : basic_stringbuf(ios_base::in | ios_base::out) {} explicit basic_stringbuf(ios_base::openmode which); explicit basic_stringbuf( const basic_string<charT, traits, Allocator>& s, ios_base::openmode which = ios_base::in | ios_base::out); explicit basic_stringbuf(const Allocator& a) : basic_stringbuf(ios_base::in | ios_base::out, a) {} basic_stringbuf(ios_base::openmode which, const Allocator& a); explicit basic_stringbuf( basic_string<charT, traits, Allocator>& s, ios_base::openmode which = ios_base::in | ios_base::out); template<class SAlloc> basic_stringbuf( const basic_string<charT, traits, SAlloc>& s, const Allocator& a) : basic_stringbuf(s, ios_base::in | ios_base::out, a) {} template<class SAlloc> basic_stringbuf( const basic_string<charT, traits, SAlloc>& s, ios_base::openmode which, const Allocator& a); template<class SAlloc> explicit basic_stringbuf( const basic_string<charT, traits, SAlloc>& s, ios_base::openmode which = ios_base::in | ios_base::out); template<class T> explicit basic_stringbuf(const T& t, ios_base::openmode which = ios_base::in | ios_base::out); template<class T> basic_stringbuf(const T& t, const Allocator& a); template<class T> basic_stringbuf(const T& t, ios_base::openmode which, const Allocator& a); basic_stringbuf(const basic_stringbuf&) = delete; basic_stringbuf(basic_stringbuf&& rhs); basic_stringbuf(basic_stringbuf&& rhs, const Allocator& a); / [stringbuf.assign], assignment and swap basic_stringbuf& operator=(const basic_stringbuf&) = delete; basic_stringbuf& operator=(basic_stringbuf&& rhs); void swap(basic_stringbuf& rhs) noexcept(see below); / [stringbuf.members], getters and setters allocator_type get_allocator() const noexcept; basic_string<charT, traits, Allocator> str() const &; template<class SAlloc> basic_string<charT,traits,SAlloc> str(const SAlloc& sa) const; basic_string<charT, traits, Allocator> str() &&; basic_string_view<charT, traits> view() const noexcept; void str(const basic_string<charT, traits, Allocator>& s); template<class SAlloc> void str(const basic_string<charT, traits, SAlloc>& s); void str(basic_string<charT, traits, Allocator>& s); template<class T> void str(const T& t); protected: / [stringbuf.virtuals], overridden virtual functions int_type underflow() override; int_type pbackfail(int_type c = traits::eof() override; int_type overflow (int_type c = traits::eof() override; basic_streambuf<charT, traits>* setbuf(charT*, streamsize) override; pos_type seekoff(off_type off, ios_base::seekdir way, ios_base::openmode which = ios_base::in | ios_base::out) override; pos_type seekpos(pos_type sp, ios_base::openmode which = ios_base::in | ios_base::out) override; private: ios_base::openmode mode; / exposition only basic_string<charT, traits, Allocator> buf; / exposition only void init-buf-ptrs(); / exposition only }; }
1
#
The class basic_stringbuf is derived from basic_streambuf to associate possibly the input sequence and possibly the output sequence with a sequence of arbitrary characters.
The sequence can be initialized from, or made available as, an object of class basic_string.
2
#
For the sake of exposition, the maintained data and internal pointer initialization is presented here as:
  • (2.1)
    ios_base​::​openmode mode, has in set if the input sequence can be read, and out set if the output sequence can be written.
  • (2.2)
    basic_string<charT, traits, Allocator> buf contains the underlying character sequence.
  • (2.3)
    init-buf-ptrs() sets the base class' get area ([streambuf.get.area]) and put area ([streambuf.put.area]) pointers after initializing, moving from, or assigning to buf accordingly.
🔗
explicit basic_stringbuf(ios_base::openmode which);
1
#
Effects: Initializes the base class with basic_streambuf() ([streambuf.cons]), and mode with which.
It is implementation-defined whether the sequence pointers (eback(), gptr(), egptr(), pbase(), pptr(), epptr()) are initialized to null pointers.
2
#
Postconditions: str().empty() is true.
🔗
explicit basic_stringbuf( const basic_string<charT, traits, Allocator>& s, ios_base::openmode which = ios_base::in | ios_base::out);
3
#
Effects: Initializes the base class with basic_streambuf() ([streambuf.cons]), mode with which, and buf with s, then calls init-buf-ptrs().
🔗
basic_stringbuf(ios_base::openmode which, const Allocator& a);
4
#
Effects: Initializes the base class with basic_streambuf() ([streambuf.cons]), mode with which, and buf with a, then calls init-buf-ptrs().
5
#
Postconditions: str().empty() is true.
🔗
explicit basic_stringbuf( basic_string<charT, traits, Allocator>& s, ios_base::openmode which = ios_base::in | ios_base::out);
6
#
Effects: Initializes the base class with basic_streambuf() ([streambuf.cons]), mode with which, and buf with std​::​move(s), then calls init-buf-ptrs().
🔗
template<class SAlloc> basic_stringbuf( const basic_string<charT, traits, SAlloc>& s, ios_base::openmode which, const Allocator& a);
7
#
Effects: Initializes the base class with basic_streambuf() ([streambuf.cons]), mode with which, and buf with {s,a}, then calls init-buf-ptrs().
🔗
template<class SAlloc> explicit basic_stringbuf( const basic_string<charT, traits, SAlloc>& s, ios_base::openmode which = ios_base::in | ios_base::out);
8
#
Effects: Initializes the base class with basic_streambuf() ([streambuf.cons]), mode with which, and buf with s, then calls init-buf-ptrs().
🔗
template<class T> explicit basic_stringbuf(const T& t, ios_base::openmode which = ios_base::in | ios_base::out); template<class T> basic_stringbuf(const T& t, const Allocator& a); template<class T> basic_stringbuf(const T& t, ios_base::openmode which, const Allocator& a);
10
#
Let which be ios_base​::​in | ios_base​::​out for the overload with no parameter which, and a be Allocator() for the overload with no parameter a.
11
#
Constraints: is_convertible_v<const T&, basic_string_view<charT, traits>> is true.
12
#
Effects: Creates a variable sv as if by basic_string_view<charT, traits> sv = t, then value-initializes the base class, initializes mode with which, and direct-non-list-initializes buf with sv, a, then calls init-buf-ptrs().
🔗
basic_stringbuf(basic_stringbuf&& rhs); basic_stringbuf(basic_stringbuf&& rhs, const Allocator& a);
13
#
Effects: Copy constructs the base class from rhs and initializes mode with rhs.mode.
In the first form buf is initialized from std​::​move(rhs).str().
In the second form buf is initialized from {std​::​move(rhs).str(), a}.
It is implementation-defined whether the sequence pointers in *this (eback(), gptr(), egptr(), pbase(), pptr(), epptr()) obtain the values which rhs had.
14
#
Postconditions: Let rhs_p refer to the state of rhs just prior to this construction and let rhs_a refer to the state of rhs just after this construction.
  • (14.1)
    str() == rhs_p.str()
  • (14.2)
    gptr() - eback() == rhs_p.gptr() - rhs_p.eback()
  • (14.3)
    egptr() - eback() == rhs_p.egptr() - rhs_p.eback()
  • (14.4)
    pptr() - pbase() == rhs_p.pptr() - rhs_p.pbase()
  • (14.5)
    epptr() - pbase() == rhs_p.epptr() - rhs_p.pbase()
  • (14.6)
    if (eback() eback() != rhs_a.eback()
  • (14.7)
    if (gptr() gptr() != rhs_a.gptr()
  • (14.8)
    if (egptr() egptr() != rhs_a.egptr()
  • (14.9)
    if (pbase() pbase() != rhs_a.pbase()
  • (14.10)
    if (pptr() pptr() != rhs_a.pptr()
  • (14.11)
    if (epptr() epptr() != rhs_a.epptr()
  • (14.12)
    getloc() == rhs_p.getloc()
  • (14.13)
    rhs is empty but usable, as if std​::​move(rhs).str() was called.

31.8.2.3 Assignment and swap [stringbuf.assign]

🔗
basic_stringbuf& operator=(basic_stringbuf&& rhs);
1
#
Effects: After the move assignment *this has the observable state it would have had if it had been move constructed from rhs (see [stringbuf.cons]).
2
#
Returns: *this.
🔗
void swap(basic_stringbuf& rhs) noexcept(see below);
3
#
Preconditions: allocator_traits<Allocator>​::​propagate_on_container_swap​::​value is true or get_allocator() == rhs.get_allocator() is true.
4
#
Effects: Exchanges the state of *this and rhs.
5
#
Remarks: The exception specification is equivalent to:
allocator_traits<Allocator>​::​propagate_on_container_swap​::​value ||
allocator_traits<Allocator>​::​is_always_equal​::​value
🔗
template<class charT, class traits, class Allocator> void swap(basic_stringbuf<charT, traits, Allocator>& x, basic_stringbuf<charT, traits, Allocator>& y) noexcept(noexcept(x.swap(y));
6
#
The member functions getting the underlying character sequence all refer to a high_mark value, where high_mark represents the position one past the highest initialized character in the buffer.
Characters can be initialized by writing to the stream, by constructing the basic_stringbuf passing a basic_string argument, or by calling one of the str member functions passing a basic_string as an argument.
In the latter case, all characters initialized prior to the call are now considered uninitialized (except for those characters re-initialized by the new basic_string).
🔗
void init-buf-ptrs();
2
#
Effects: Initializes the input and output sequences from buf according to mode.
3
#
Postconditions:
  • (3.1)
    If ios_base​::​out is set in mode, pbase() points to buf.front() and epptr() >= pbase() + buf.size() is true;
    • (3.1.1)
      in addition, if ios_base​::​ate is set in mode, pptr() == pbase() + buf.size() is true,
    • (3.1.2)
      otherwise pptr() == pbase() is true.
  • (3.2)
    If ios_base​::​in is set in mode, eback() points to buf.front(), and (gptr() == eback() && egptr() == eback() + buf.size() is true.
4
#
[Note 1: 
For efficiency reasons, stream buffer operations can violate invariants of buf while it is held encapsulated in the basic_stringbuf, e.g., by writing to characters in the range [buf.data() + buf.size(), buf.data() + buf.capacity()).
All operations retrieving a basic_string from buf ensure that the basic_string invariants hold on the returned value.
— end note]
🔗
allocator_type get_allocator() const noexcept;
5
#
Returns: buf.get_allocator().
🔗
basic_string<charT, traits, Allocator> str() const &;
6
#
Effects: Equivalent to: return basic_string<charT, traits, Allocator>(view(), get_allocator();
🔗
template<class SAlloc> basic_string<charT, traits, SAlloc> str(const SAlloc& sa) const;
7
#
Constraints: SAlloc is a type that qualifies as an allocator ([container.reqmts]).
8
#
Effects: Equivalent to: return basic_string<charT, traits, SAlloc>(view(), sa);
🔗
basic_string<charT, traits, Allocator> str() &&;
9
#
Postconditions: The underlying character sequence buf is empty and pbase(), pptr(), epptr(), eback(), gptr(), and egptr() are initialized as if by calling init-buf-ptrs() with an empty buf.
10
#
Returns: A basic_string<charT, traits, Allocator> object move constructed from the basic_stringbuf's underlying character sequence in buf.
This can be achieved by first adjusting buf to have the same content as view().
🔗
basic_string_view<charT, traits> view() const noexcept;
11
#
Returns: A sv object referring to the basic_stringbuf's underlying character sequence in buf:
  • (12.1)
    If ios_base​::​out is set in mode, then sv(pbase(), high_mark - pbase() is returned.
  • (12.2)
    Otherwise, if ios_base​::​in is set in mode, then sv(eback(), egptr() - eback() is returned.
  • (12.3)
    Otherwise, sv() is returned.
13
#
[Note 2: 
Using the returned sv object after destruction or invalidation of the character sequence underlying *this is undefined behavior, unless sv.empty() is true.
— end note]
🔗
void str(const basic_string<charT, traits, Allocator>& s);
14
#
Effects: Equivalent to: buf = s; init-buf-ptrs();
🔗
template<class SAlloc> void str(const basic_string<charT, traits, SAlloc>& s);
15
#
Effects: Equivalent to: buf = s; init-buf-ptrs();
🔗
void str(basic_string<charT, traits, Allocator>& s);
17
#
Effects: Equivalent to: buf = std::move(s); init-buf-ptrs();
🔗
template<class T> void str(const T& t);
18
#
Constraints: is_convertible_v<const T&, basic_string_view<charT, traits>> is true.
19
#
Effects: Equivalent to: basic_string_view<charT, traits> sv = t; buf = sv; init-buf-ptrs();

31.8.2.5 Overridden virtual functions [stringbuf.virtuals]

🔗
int_type underflow() override;
1
#
Returns: If the input sequence has a read position available, returns traits​::​to_int_type(*gptr().
Otherwise, returns traits​::​eof().
Any character in the underlying buffer which has been initialized is considered to be part of the input sequence.
🔗
int_type pbackfail(int_type c = traits::eof() override;
2
#
Effects: Puts back the character designated by c to the input sequence, if possible, in one of three ways:
  • (2.1)
    If traits​::​eq_int_type(c, traits​::​eof() returns false and if the input sequence has a putback position available, and if traits​::​eq(to_char_type(c), gptr()[-1]) returns true, assigns gptr() - 1 to gptr().
    Returns: c.
  • (2.2)
    If traits​::​eq_int_type(c, traits​::​eof() returns false and if the input sequence has a putback position available, and if mode & ios_base​::​out is nonzero, assigns c to *-gptr().
    Returns: c.
  • (2.3)
    If traits​::​eq_int_type(c, traits​::​eof() returns true and if the input sequence has a putback position available, assigns gptr() - 1 to gptr().
    Returns: traits​::​not_eof(c).
3
#
Returns: As specified above, or traits​::​eof() to indicate failure.
4
#
Remarks: If the function can succeed in more than one of these ways, it is unspecified which way is chosen.
🔗
int_type overflow(int_type c = traits::eof() override;
5
#
Effects: Appends the character designated by c to the output sequence, if possible, in one of two ways:
  • (5.1)
    If traits​::​eq_int_type(c, traits​::​eof() returns false and if either the output sequence has a write position available or the function makes a write position available (as described below), the function calls sputc(c).
    Signals success by returning c.
  • (5.2)
    If traits​::​eq_int_type(c, traits​::​eof() returns true, there is no character to append.
    Signals success by returning a value other than traits​::​eof().
6
#
Returns: As specified above, or traits​::​eof() to indicate failure.
7
#
Remarks: The function can alter the number of write positions available as a result of any call.
8
#
The function can make a write position available only if ios_base​::​out is set in mode.
To make a write position available, the function reallocates (or initially allocates) an array object with a sufficient number of elements to hold the current array object (if any), plus at least one additional write position.
If ios_base​::​in is set in mode, the function alters the read end pointer egptr() to point just past the new write position.
🔗
pos_type seekoff(off_type off, ios_base::seekdir way, ios_base::openmode which = ios_base::in | ios_base::out) override;
9
#
Effects: Alters the stream position within one of the controlled sequences, if possible, as indicated in Table 144.
Table 144 — seekoff positioning [tab:stringbuf.seekoff.pos]
🔗
Conditions
Result
🔗
ios_base​::​in is set in which
positions the input sequence
🔗
ios_base​::​out is set in which
positions the output sequence
🔗
both ios_base​::​in and ios_base​::​out are set in which and either
way == ios_base​::​beg or
way == ios_base​::​end
positions both the input and the output sequences
🔗
Otherwise
the positioning operation fails.
10
#
For a sequence to be positioned, the function determines newoff as indicated in Table 145.
If the sequence's next pointer (either gptr() or pptr()) is a null pointer and newoff is nonzero, the positioning operation fails.
Table 145 — newoff values [tab:stringbuf.seekoff.newoff]
🔗
Condition
newoff Value
🔗
way == ios_base​::​beg
0
🔗
way == ios_base​::​cur
the next pointer minus the beginning pointer (xnext - xbeg).
🔗
way == ios_base​::​end
the high mark pointer minus the beginning pointer (high_mark - xbeg).
11
#
If (newoff + off) < 0, or if newoff + off refers to an uninitialized character ([stringbuf.members]), the positioning operation fails.
Otherwise, the function assigns xbeg + newoff + off to the next pointer xnext.
12
#
Returns: pos_type(newoff), constructed from the resultant offset newoff (of type off_type), that stores the resultant stream position, if possible.
If the positioning operation fails, or if the constructed object cannot represent the resultant stream position, the return value is pos_type(off_type(-1).
🔗
pos_type seekpos(pos_type sp, ios_base::openmode which = ios_base::in | ios_base::out) override;
13
#
Returns: sp to indicate success, or pos_type(off_type(-1) to indicate failure.
🔗
basic_streambuf<charT, traits>* setbuf(charT* s, streamsize n) override;
15
#
Effects: implementation-defined, except that setbuf(0, 0) has no effect.
16
#
Returns: this.

31.8.3 Class template basic_istringstream [istringstream]

🔗
namespace std { template<class charT, class traits = char_traits<charT>, class Allocator = allocator<charT>> class basic_istringstream : public basic_istream<charT, traits> { public: using char_type = charT; using int_type = traits::int_type; using pos_type = traits::pos_type; using off_type = traits::off_type; using traits_type = traits; using allocator_type = Allocator; / [istringstream.cons], constructors basic_istringstream() : basic_istringstream(ios_base::in) {} explicit basic_istringstream(ios_base::openmode which); explicit basic_istringstream( const basic_string<charT, traits, Allocator>& s, ios_base::openmode which = ios_base::in); basic_istringstream(ios_base::openmode which, const Allocator& a); explicit basic_istringstream( basic_string<charT, traits, Allocator>& s, ios_base::openmode which = ios_base::in); template<class SAlloc> basic_istringstream( const basic_string<charT, traits, SAlloc>& s, const Allocator& a) : basic_istringstream(s, ios_base::in, a) {} template<class SAlloc> basic_istringstream( const basic_string<charT, traits, SAlloc>& s, ios_base::openmode which, const Allocator& a); template<class SAlloc> explicit basic_istringstream( const basic_string<charT, traits, SAlloc>& s, ios_base::openmode which = ios_base::in); template<class T> explicit basic_istringstream(const T& t, ios_base::openmode which = ios_base::in); template<class T> basic_istringstream(const T& t, const Allocator& a); template<class T> basic_istringstream(const T& t, ios_base::openmode which, const Allocator& a); basic_istringstream(const basic_istringstream&) = delete; basic_istringstream(basic_istringstream&& rhs); basic_istringstream& operator=(const basic_istringstream&) = delete; basic_istringstream& operator=(basic_istringstream&& rhs); / [istringstream.swap], swap void swap(basic_istringstream& rhs); / [istringstream.members], members basic_stringbuf<charT, traits, Allocator>* rdbuf() const; basic_string<charT, traits, Allocator> str() const &; template<class SAlloc> basic_string<charT,traits,SAlloc> str(const SAlloc& sa) const; basic_string<charT, traits, Allocator> str() &&; basic_string_view<charT, traits> view() const noexcept; void str(const basic_string<charT, traits, Allocator>& s); template<class SAlloc> void str(const basic_string<charT, traits, SAlloc>& s); void str(basic_string<charT, traits, Allocator>& s); template<class T> void str(const T& t); private: basic_stringbuf<charT, traits, Allocator> sb; / exposition only }; }
1
#
The class basic_istringstream<charT, traits, Allocator> supports reading objects of class basic_string<​charT, traits, Allocator>.
It uses a basic_stringbuf<charT, traits, Allocator> object to control the associated storage.
For the sake of exposition, the maintained data is presented here as:
  • (1.1)
    sb, the stringbuf object.
🔗
explicit basic_istringstream(ios_base::openmode which);
1
#
Effects: Initializes the base class with basic_istream<charT, traits>(addressof(sb) ([istream]) and sb with basic_stringbuf<charT, traits, Allocator>(which | ios_base​::​in) ([stringbuf.cons]).
🔗
explicit basic_istringstream( const basic_string<charT, traits, Allocator>& s, ios_base::openmode which = ios_base::in);
2
#
Effects: Initializes the base class with basic_istream<charT, traits>(addressof(sb) ([istream]) and sb with basic_stringbuf<charT, traits, Allocator>(s, which | ios_base​::​in)
([stringbuf.cons]).
🔗
basic_istringstream(ios_base::openmode which, const Allocator& a);
3
#
Effects: Initializes the base class with basic_istream<charT, traits>(addressof(sb) ([istream]) and sb with basic_stringbuf<charT, traits, Allocator>(which | ios_base​::​in, a) ([stringbuf.cons]).
🔗
explicit basic_istringstream( basic_string<charT, traits, Allocator>& s, ios_base::openmode which = ios_base::in);
4
#
Effects: Initializes the base class with basic_istream<charT, traits>(addressof(sb) ([istream]) and sb with basic_stringbuf<charT, traits, Allocator>(std​::​move(s), which | ios_base​::​​in) ([stringbuf.cons]).
🔗
template<class SAlloc> basic_istringstream( const basic_string<charT, traits, SAlloc>& s, ios_base::openmode which, const Allocator& a);
5
#
Effects: Initializes the base class with basic_istream<charT, traits>(addressof(sb) ([istream]) and sb with basic_stringbuf<charT, traits, Allocator>(s, which | ios_base​::​in, a)
([stringbuf.cons]).
🔗
template<class SAlloc> explicit basic_istringstream( const basic_string<charT, traits, SAlloc>& s, ios_base::openmode which = ios_base::in);
6
#
Effects: Initializes the base class with basic_istream<charT, traits>(addressof(sb) ([istream]) and sb with basic_stringbuf<charT, traits, Allocator>(s, which | ios_base​::​in) ([stringbuf.cons]).
🔗
template<class T> explicit basic_istringstream(const T& t, ios_base::openmode which = ios_base::in); template<class T> basic_istringstream(const T& t, const Allocator& a); template<class T> basic_istringstream(const T& t, ios_base::openmode which, const Allocator& a);
8
#
Let which be ios_base​::​in for the overload with no parameter which, and a be Allocator() for the overload with no parameter a.
9
#
Constraints: is_convertible_v<const T&, basic_string_view<charT, traits>> is true.
10
#
Effects: Initializes the base class with addressof(sb), and direct-non-list-initializes sb with t, which | ios_base​::​in, a.
🔗
basic_istringstream(basic_istringstream&& rhs);
11
#
Effects: Move constructs from the rvalue rhs.
This is accomplished by move constructing the base class, and the contained basic_stringbuf.
Then calls basic_istream<charT, traits>​::​set_rdbuf(addressof(sb) to install the contained basic_stringbuf.
🔗
void swap(basic_istringstream& rhs);
1
#
Effects: Equivalent to: basic_istream<charT, traits>::swap(rhs); sb.swap(rhs.sb);
🔗
template<class charT, class traits, class Allocator> void swap(basic_istringstream<charT, traits, Allocator>& x, basic_istringstream<charT, traits, Allocator>& y);
2
#
Effects: Equivalent to x.swap(y).
🔗
basic_stringbuf<charT, traits, Allocator>* rdbuf() const;
1
#
Returns: const_cast<basic_stringbuf<charT, traits, Allocator>*>(addressof(sb).
🔗
basic_string<charT, traits, Allocator> str() const &;
2
#
Effects: Equivalent to: return rdbuf()->str();
🔗
template<class SAlloc> basic_string<charT,traits,SAlloc> str(const SAlloc& sa) const;
3
#
Effects: Equivalent to: return rdbuf()->str(sa);
🔗
basic_string<charT,traits,Allocator> str() &&;
4
#
Effects: Equivalent to: return std​::​move(*rdbuf().str();
🔗
basic_string_view<charT, traits> view() const noexcept;
5
#
Effects: Equivalent to: return rdbuf()->view();
🔗
void str(const basic_string<charT, traits, Allocator>& s);
6
#
Effects: Equivalent to: rdbuf()->str(s);
🔗
template<class SAlloc> void str(const basic_string<charT, traits, SAlloc>& s);
7
#
Effects: Equivalent to: rdbuf()->str(s);
🔗
void str(basic_string<charT, traits, Allocator>& s);
8
#
Effects: Equivalent to: rdbuf()->str(std​::​move(s));
🔗
template<class T> void str(const T& t);
9
#
Constraints: is_convertible_v<const T&, basic_string_view<charT, traits>> is true.
10
#
Effects: Equivalent to: rdbuf()->str(t);

31.8.4 Class template basic_ostringstream [ostringstream]

🔗
namespace std { template<class charT, class traits = char_traits<charT>, class Allocator = allocator<charT>> class basic_ostringstream : public basic_ostream<charT, traits> { public: using char_type = charT; using int_type = traits::int_type; using pos_type = traits::pos_type; using off_type = traits::off_type; using traits_type = traits; using allocator_type = Allocator; / [ostringstream.cons], constructors basic_ostringstream() : basic_ostringstream(ios_base::out) {} explicit basic_ostringstream(ios_base::openmode which); explicit basic_ostringstream( const basic_string<charT, traits, Allocator>& s, ios_base::openmode which = ios_base::out); basic_ostringstream(ios_base::openmode which, const Allocator& a); explicit basic_ostringstream( basic_string<charT, traits, Allocator>& s, ios_base::openmode which = ios_base::out); template<class SAlloc> basic_ostringstream( const basic_string<charT, traits, SAlloc>& s, const Allocator& a) : basic_ostringstream(s, ios_base::out, a) {} template<class SAlloc> basic_ostringstream( const basic_string<charT, traits, SAlloc>& s, ios_base::openmode which, const Allocator& a); template<class SAlloc> explicit basic_ostringstream( const basic_string<charT, traits, SAlloc>& s, ios_base::openmode which = ios_base::out); template<class T> explicit basic_ostringstream(const T& t, ios_base::openmode which = ios_base::out); template<class T> basic_ostringstream(const T& t, const Allocator& a); template<class T> basic_ostringstream(const T& t, ios_base::openmode which, const Allocator& a); basic_ostringstream(const basic_ostringstream&) = delete; basic_ostringstream(basic_ostringstream&& rhs); basic_ostringstream& operator=(const basic_ostringstream&) = delete; basic_ostringstream& operator=(basic_ostringstream&& rhs); / [ostringstream.swap], swap void swap(basic_ostringstream& rhs); / [ostringstream.members], members basic_stringbuf<charT, traits, Allocator>* rdbuf() const; basic_string<charT, traits, Allocator> str() const &; template<class SAlloc> basic_string<charT,traits,SAlloc> str(const SAlloc& sa) const; basic_string<charT, traits, Allocator> str() &&; basic_string_view<charT, traits> view() const noexcept; void str(const basic_string<charT, traits, Allocator>& s); template<class SAlloc> void str(const basic_string<charT, traits, SAlloc>& s); void str(basic_string<charT, traits, Allocator>& s); template<class T> void str(const T& t); private: basic_stringbuf<charT, traits, Allocator> sb; / exposition only }; }
1
#
The class basic_ostringstream<charT, traits, Allocator> supports writing objects of class basic_string<​charT, traits, Allocator>.
It uses a basic_stringbuf object to control the associated storage.
For the sake of exposition, the maintained data is presented here as:
  • (1.1)
    sb, the stringbuf object.
🔗
explicit basic_ostringstream(ios_base::openmode which);
1
#
Effects: Initializes the base class with basic_ostream<charT, traits>(addressof(sb) ([ostream]) and sb with basic_stringbuf<charT, traits, Allocator>(which | ios_base​::​out) ([stringbuf.cons]).
🔗
explicit basic_ostringstream( const basic_string<charT, traits, Allocator>& s, ios_base::openmode which = ios_base::out);
2
#
Effects: Initializes the base class with basic_ostream<charT, traits>(addressof(sb) ([ostream]) and sb with basic_stringbuf<charT, traits, Allocator>(s, which | ios_base​::​out)
([stringbuf.cons]).
🔗
basic_ostringstream(ios_base::openmode which, const Allocator& a);
3
#
Effects: Initializes the base class with basic_ostream<charT, traits>(addressof(sb) ([ostream]) and sb with basic_stringbuf<charT, traits, Allocator>(which | ios_base​::​out, a)
([stringbuf.cons]).
🔗
explicit basic_ostringstream( basic_string<charT, traits, Allocator>& s, ios_base::openmode which = ios_base::out);
4
#
Effects: Initializes the base class with basic_ostream<charT, traits>(addressof(sb) ([ostream]) and sb with basic_stringbuf<charT, traits, Allocator>(std​::​move(s), which | ios_base​::​​out) ([stringbuf.cons]).
🔗
template<class SAlloc> basic_ostringstream( const basic_string<charT, traits, SAlloc>& s, ios_base::openmode which, const Allocator& a);
5
#
Effects: Initializes the base class with basic_ostream<charT, traits>(addressof(sb) ([ostream]) and sb with basic_stringbuf<charT, traits, Allocator>(s, which | ios_base​::​out, a)
([stringbuf.cons]).
🔗
template<class SAlloc> explicit basic_ostringstream( const basic_string<charT, traits, SAlloc>& s, ios_base::openmode which = ios_base::out);
6
#
Effects: Initializes the base class with basic_ostream<charT, traits>(addressof(sb) ([ostream]) and sb with basic_stringbuf<charT, traits, Allocator>(s, which | ios_base​::​out)
([stringbuf.cons]).
🔗
template<class T> explicit basic_ostringstream(const T& t, ios_base::openmode which = ios_base::out); template<class T> basic_ostringstream(const T& t, const Allocator& a); template<class T> basic_ostringstream(const T& t, ios_base::openmode which, const Allocator& a);
8
#
Let which be ios_base​::​out for the overload with no parameter which, and a be Allocator() for the overload with no parameter a.
9
#
Constraints: is_convertible_v<const T&, basic_string_view<charT, traits>> is true.
10
#
Effects: Initializes the base class with addressof(sb), and direct-non-list-initializes sb with t, which | ios_base​::​out, a.
🔗
basic_ostringstream(basic_ostringstream&& rhs);
11
#
Effects: Move constructs from the rvalue rhs.
This is accomplished by move constructing the base class, and the contained basic_stringbuf.
Then calls basic_ostream<charT, traits>​::​set_rdbuf(addressof(sb) to install the contained basic_stringbuf.
🔗
void swap(basic_ostringstream& rhs);
1
#
Effects: Equivalent to: basic_ostream<charT, traits>::swap(rhs); sb.swap(rhs.sb);
🔗
template<class charT, class traits, class Allocator> void swap(basic_ostringstream<charT, traits, Allocator>& x, basic_ostringstream<charT, traits, Allocator>& y);
2
#
Effects: Equivalent to x.swap(y).
🔗
basic_stringbuf<charT, traits, Allocator>* rdbuf() const;
1
#
Returns: const_cast<basic_stringbuf<charT, traits, Allocator>*>(addressof(sb).
🔗
basic_string<charT, traits, Allocator> str() const &;
2
#
Effects: Equivalent to: return rdbuf()->str();
🔗
template<class SAlloc> basic_string<charT,traits,SAlloc> str(const SAlloc& sa) const;
3
#
Effects: Equivalent to: return rdbuf()->str(sa);
🔗
basic_string<charT,traits,Allocator> str() &&;
4
#
Effects: Equivalent to: return std​::​move(*rdbuf().str();
🔗
basic_string_view<charT, traits> view() const noexcept;
5
#
Effects: Equivalent to: return rdbuf()->view();
🔗
void str(const basic_string<charT, traits, Allocator>& s);
6
#
Effects: Equivalent to: rdbuf()->str(s);
🔗
template<class SAlloc> void str(const basic_string<charT, traits, SAlloc>& s);
7
#
Effects: Equivalent to: rdbuf()->str(s);
🔗
void str(basic_string<charT, traits, Allocator>& s);
8
#
Effects: Equivalent to: rdbuf()->str(std​::​move(s));
🔗
template<class T> void str(const T& t);
9
#
Constraints: is_convertible_v<const T&, basic_string_view<charT, traits>> is true.
10
#
Effects: Equivalent to: rdbuf()->str(t);

31.8.5 Class template basic_stringstream [stringstream]

🔗
namespace std { template<class charT, class traits = char_traits<charT>, class Allocator = allocator<charT>> class basic_stringstream : public basic_iostream<charT, traits> { public: using char_type = charT; using int_type = traits::int_type; using pos_type = traits::pos_type; using off_type = traits::off_type; using traits_type = traits; using allocator_type = Allocator; / [stringstream.cons], constructors basic_stringstream() : basic_stringstream(ios_base::out | ios_base::in) {} explicit basic_stringstream(ios_base::openmode which); explicit basic_stringstream( const basic_string<charT, traits, Allocator>& s, ios_base::openmode which = ios_base::out | ios_base::in); basic_stringstream(ios_base::openmode which, const Allocator& a); explicit basic_stringstream( basic_string<charT, traits, Allocator>& s, ios_base::openmode which = ios_base::out | ios_base::in); template<class SAlloc> basic_stringstream( const basic_string<charT, traits, SAlloc>& s, const Allocator& a) : basic_stringstream(s, ios_base::out | ios_base::in, a) {} template<class SAlloc> basic_stringstream( const basic_string<charT, traits, SAlloc>& s, ios_base::openmode which, const Allocator& a); template<class SAlloc> explicit basic_stringstream( const basic_string<charT, traits, SAlloc>& s, ios_base::openmode which = ios_base::out | ios_base::in); template<class T> explicit basic_stringstream(const T& t, ios_base::openmode which = ios_base::out | ios_base::in); template<class T> basic_stringstream(const T& t, const Allocator& a); template<class T> basic_stringstream(const T& t, ios_base::openmode which, const Allocator& a); basic_stringstream(const basic_stringstream&) = delete; basic_stringstream(basic_stringstream&& rhs); basic_stringstream& operator=(const basic_stringstream&) = delete; basic_stringstream& operator=(basic_stringstream&& rhs); / [stringstream.swap], swap void swap(basic_stringstream& rhs); / [stringstream.members], members basic_stringbuf<charT, traits, Allocator>* rdbuf() const; basic_string<charT, traits, Allocator> str() const &; template<class SAlloc> basic_string<charT,traits,SAlloc> str(const SAlloc& sa) const; basic_string<charT, traits, Allocator> str() &&; basic_string_view<charT, traits> view() const noexcept; void str(const basic_string<charT, traits, Allocator>& s); template<class SAlloc> void str(const basic_string<charT, traits, SAlloc>& s); void str(basic_string<charT, traits, Allocator>& s); template<class T> void str(const T& t); private: basic_stringbuf<charT, traits, Allocator> sb; / exposition only }; }
1
#
The class template basic_stringstream<charT, traits> supports reading and writing from objects of class basic_string<charT, traits, Allocator>.
It uses a basic_stringbuf<charT, traits, Allocator> object to control the associated sequence.
For the sake of exposition, the maintained data is presented here as
  • (1.1)
    sb, the stringbuf object.
🔗
explicit basic_stringstream(ios_base::openmode which);
1
#
Effects: Initializes the base class with basic_iostream<charT, traits>(addressof(sb) ([iostream.cons]) and sb with basic_stringbuf<charT, traits, Allocator>(which).
🔗
explicit basic_stringstream( const basic_string<charT, traits, Allocator>& s, ios_base::openmode which = ios_base::out | ios_base::in);
2
#
Effects: Initializes the base class with basic_iostream<charT, traits>(addressof(sb) ([iostream.cons]) and sb with basic_stringbuf<charT, traits, Allocator>(s, which).
🔗
basic_stringstream(ios_base::openmode which, const Allocator& a);
3
#
Effects: Initializes the base class with basic_iostream<charT, traits>(addressof(sb) ([iostream.cons]) and sb with basic_stringbuf<charT, traits, Allocator>(which, a) ([stringbuf.cons]).
🔗
explicit basic_stringstream( basic_string<charT, traits, Allocator>& s, ios_base::openmode which = ios_base::out | ios_base::in);
4
#
Effects: Initializes the base class with basic_iostream<charT, traits>(addressof(sb) ([iostream.cons]) and sb with basic_stringbuf<charT, traits, Allocator>(std​::​move(s), which) ([stringbuf.cons]).
🔗
template<class SAlloc> basic_stringstream( const basic_string<charT, traits, SAlloc>& s, ios_base::openmode which, const Allocator& a);
5
#
Effects: Initializes the base class with basic_iostream<charT, traits>(addressof(sb) ([iostream.cons]) and sb with basic_stringbuf<charT, traits, Allocator>(s, which, a) ([stringbuf.cons]).
🔗
template<class SAlloc> explicit basic_stringstream( const basic_string<charT, traits, SAlloc>& s, ios_base::openmode which = ios_base::out | ios_base::in);
6
#
Effects: Initializes the base class with basic_iostream<charT, traits>(addressof(sb) ([iostream.cons]) and sb with basic_stringbuf<charT, traits, Allocator>(s, which) ([stringbuf.cons]).
🔗
template<class T> explicit basic_stringstream(const T& t, ios_base::openmode which = ios_base::out | ios_base::in); template<class T> basic_stringstream(const T& t, const Allocator& a); template<class T> basic_stringstream(const T& t, ios_base::openmode which, const Allocator& a);
8
#
Let which be ios_base​::​out | ios_base​::​in for the overload with no parameter which, and a be Allocator() for the overload with no parameter a.
9
#
Constraints: is_convertible_v<const T&, basic_string_view<charT, traits>> is true.
10
#
Effects: Initializes the base class with addressof(sb), and direct-non-list-initializes sb with t, which, a.
🔗
basic_stringstream(basic_stringstream&& rhs);
11
#
Effects: Move constructs from the rvalue rhs.
This is accomplished by move constructing the base class, and the contained basic_stringbuf.
Then calls basic_istream<charT, traits>​::​set_rdbuf(addressof(sb) to install the contained basic_stringbuf.
🔗
void swap(basic_stringstream& rhs);
1
#
Effects: Equivalent to: basic_iostream<charT,traits>::swap(rhs); sb.swap(rhs.sb);
🔗
template<class charT, class traits, class Allocator> void swap(basic_stringstream<charT, traits, Allocator>& x, basic_stringstream<charT, traits, Allocator>& y);
2
#
Effects: Equivalent to x.swap(y).
🔗
basic_stringbuf<charT, traits, Allocator>* rdbuf() const;
1
#
Returns: const_cast<basic_stringbuf<charT, traits, Allocator>*>(addressof(sb).
🔗
basic_string<charT, traits, Allocator> str() const &;
2
#
Effects: Equivalent to: return rdbuf()->str();
🔗
template<class SAlloc> basic_string<charT,traits,SAlloc> str(const SAlloc& sa) const;
3
#
Effects: Equivalent to: return rdbuf()->str(sa);
🔗
basic_string<charT,traits,Allocator> str() &&;
4
#
Effects: Equivalent to: return std​::​move(*rdbuf().str();
🔗
basic_string_view<charT, traits> view() const noexcept;
5
#
Effects: Equivalent to: return rdbuf()->view();
🔗
void str(const basic_string<charT, traits, Allocator>& s);
6
#
Effects: Equivalent to: rdbuf()->str(s);
🔗
template<class SAlloc> void str(const basic_string<charT, traits, SAlloc>& s);
7
#
Effects: Equivalent to: rdbuf()->str(s);
🔗
void str(basic_string<charT, traits, Allocator>& s);
8
#
Effects: Equivalent to: rdbuf()->str(std​::​move(s));
🔗
template<class T> void str(const T& t);
9
#
Constraints: is_convertible_v<const T&, basic_string_view<charT, traits>> is true.
10
#
The header <spanstream> defines class templates and types that associate stream buffers with objects whose types are specializations of span as described in [views.span].
[Note 1: 
A user of these classes is responsible for ensuring that the character sequence represented by the given span outlives the use of the sequence by objects of the classes in [span.streams].
Using multiple basic_spanbuf objects referring to overlapping underlying sequences from different threads, where at least one basic_spanbuf object is used for writing to the sequence, results in a data race.
— end note]

31.9.2 Header <spanstream> synopsis [spanstream.syn]

🔗
namespace std { / [spanbuf], class template basic_spanbuf template<class charT, class traits = char_traits<charT>> class basic_spanbuf; template<class charT, class traits> void swap(basic_spanbuf<charT, traits>& x, basic_spanbuf<charT, traits>& y); using spanbuf = basic_spanbuf<char>; using wspanbuf = basic_spanbuf<wchar_t>; / [ispanstream], class template basic_ispanstream template<class charT, class traits = char_traits<charT>> class basic_ispanstream; template<class charT, class traits> void swap(basic_ispanstream<charT, traits>& x, basic_ispanstream<charT, traits>& y); using ispanstream = basic_ispanstream<char>; using wispanstream = basic_ispanstream<wchar_t>; / [ospanstream], class template basic_ospanstream template<class charT, class traits = char_traits<charT>> class basic_ospanstream; template<class charT, class traits> void swap(basic_ospanstream<charT, traits>& x, basic_ospanstream<charT, traits>& y); using ospanstream = basic_ospanstream<char>; using wospanstream = basic_ospanstream<wchar_t>; / [spanstream], class template basic_spanstream template<class charT, class traits = char_traits<charT>> class basic_spanstream; template<class charT, class traits> void swap(basic_spanstream<charT, traits>& x, basic_spanstream<charT, traits>& y); using spanstream = basic_spanstream<char>; using wspanstream = basic_spanstream<wchar_t>; }

31.9.3 Class template basic_spanbuf [spanbuf]

🔗
namespace std { template<class charT, class traits = char_traits<charT>> class basic_spanbuf : public basic_streambuf<charT, traits> { public: using char_type = charT; using int_type = traits::int_type; using pos_type = traits::pos_type; using off_type = traits::off_type; using traits_type = traits; / [spanbuf.cons], constructors basic_spanbuf() : basic_spanbuf(ios_base::in | ios_base::out) {} explicit basic_spanbuf(ios_base::openmode which) : basic_spanbuf(std::span<charT>(), which) {} explicit basic_spanbuf(std::span<charT> s, ios_base::openmode which = ios_base::in | ios_base::out); basic_spanbuf(const basic_spanbuf&) = delete; basic_spanbuf(basic_spanbuf&& rhs); / [spanbuf.assign], assignment and swap basic_spanbuf& operator=(const basic_spanbuf&) = delete; basic_spanbuf& operator=(basic_spanbuf&& rhs); void swap(basic_spanbuf& rhs); / [spanbuf.members], member functions std::span<charT> span() const noexcept; void span(std::span<charT> s) noexcept; protected: / [spanbuf.virtuals], overridden virtual functions basic_streambuf<charT, traits>* setbuf(charT*, streamsize) override; pos_type seekoff(off_type off, ios_base::seekdir way, ios_base::openmode which = ios_base::in | ios_base::out) override; pos_type seekpos(pos_type sp, ios_base::openmode which = ios_base::in | ios_base::out) override; private: ios_base::openmode mode; / exposition only std::span<charT> buf; / exposition only }; }
1
#
The class template basic_spanbuf is derived from basic_streambuf to associate possibly the input sequence and possibly the output sequence with a sequence of arbitrary characters.
The sequence is provided by an object of class span<charT>.
2
#
For the sake of exposition, the maintained data is presented here as:
  • (2.1)
    ios_base​::​openmode mode, has in set if the input sequence can be read, and out set if the output sequence can be written.
  • (2.2)
    std​::​span<charT> buf is the view to the underlying character sequence.
🔗
explicit basic_spanbuf(std::span<charT> s, ios_base::openmode which = ios_base::in | ios_base::out);
1
#
Effects: Initializes the base class with basic_streambuf() ([streambuf.cons]), and mode with which.
Initializes the internal pointers as if calling span(s).
🔗
basic_spanbuf(basic_spanbuf&& rhs);
2
#
Effects: Initializes the base class with std​::​move(rhs) and mode with std​::​move(rhs.mode) and buf with std​::​move(rhs.buf).
The sequence pointers in *this (eback(), gptr(), egptr(), pbase(), pptr(), epptr()) obtain the values which rhs had.
It is implementation-defined whether rhs.buf.​empty() returns true after the move.
3
#
Postconditions: Let rhs_p refer to the state of rhs just prior to this construction.
  • (3.1)
    span().data() == rhs_p.span().data()
  • (3.2)
    span().size() == rhs_p.span().size()
  • (3.3)
    eback() == rhs_p.eback()
  • (3.4)
    gptr() == rhs_p.gptr()
  • (3.5)
    egptr() == rhs_p.egptr()
  • (3.6)
    pbase() == rhs_p.pbase()
  • (3.7)
    pptr() == rhs_p.pptr()
  • (3.8)
    epptr() == rhs_p.epptr()
  • (3.9)
    getloc() == rhs_p.getloc()

31.9.3.3 Assignment and swap [spanbuf.assign]

🔗
basic_spanbuf& operator=(basic_spanbuf&& rhs);
1
#
Effects: Equivalent to: basic_spanbuf tmp{std::move(rhs)}; this->swap(tmp); return *this;
🔗
void swap(basic_spanbuf& rhs);
2
#
Effects: Equivalent to: basic_streambuf<charT, traits>::swap(rhs); std::swap(mode, rhs.mode); std::swap(buf, rhs.buf);
🔗
template<class charT, class traits> void swap(basic_spanbuf<charT, traits>& x, basic_spanbuf<charT, traits>& y);
3
#
Effects: Equivalent to x.swap(y).

31.9.3.4 Member functions [spanbuf.members]

🔗
std::span<charT> span() const noexcept;
1
#
Returns: If ios_base​::​out is set in mode, returns std​::​span<charT>(pbase(), pptr(), otherwise returns buf.
[Note 1: 
In contrast to basic_stringbuf, the underlying sequence never grows and is not owned.
An owning copy can be obtained by converting the result to basic_string<charT>.
— end note]
🔗
void span(std::span<charT> s) noexcept;
2
#
Postconditions:
  • (3.1)
    If ios_base​::​out is set in mode, pbase() == s.data() && epptr() == pbase() + s.size() is true;
    • (3.1.1)
      in addition, if ios_base​::​ate is set in mode, pptr() == pbase() + s.size() is true,
    • (3.1.2)
      otherwise pptr() == pbase() is true.
  • (3.2)
    If ios_base​::​in is set in mode, eback() == s.data() && gptr() == eback() && egptr() == eback() + s.size() is true.

31.9.3.5 Overridden virtual functions [spanbuf.virtuals]

1
#
[Note 1: 
Because the underlying buffer is of fixed size, neither overflow, underflow, nor pbackfail can provide useful behavior.
— end note]
🔗
pos_type seekoff(off_type off, ios_base::seekdir way, ios_base::openmode which = ios_base::in | ios_base::out) override;
2
#
Effects: Alters the stream position within one or both of the controlled sequences, if possible, as follows:
  • (2.1)
    If ios_base​::​in is set in which, positions the input sequence; xnext is gptr(), xbeg is eback().
  • (2.2)
    If ios_base​::​out is set in which, positions the output sequence; xnext is pptr(), xbeg is pbase().
3
#
If both ios_base​::​in and ios_base​::​out are set in which and way is ios_base​::​cur, the positioning operation fails.
4
#
For a sequence to be positioned, if its next pointer xnext (either gptr() or pptr()) is a null pointer and the new offset newoff as computed below is nonzero, the positioning operation fails.
Otherwise, the function determines baseoff as a value of type off_type as follows:
  • (4.1)
    0 when way is ios_base​::​beg;
  • (4.2)
    (pptr() - pbase() for the output sequence, or (gptr() - eback() for the input sequence when way is ios_base​::​cur;
  • (4.3)
    when way is ios_base​::​end :
    • (4.3.1)
      (pptr() - pbase() if ios_base​::​out is set in mode and ios_base​::​in is not set in mode,
    • (4.3.2)
      buf.size() otherwise.
5
#
If
Otherwise, the function computes off_type newoff = baseoff + off; and assigns xbeg + newoff to the next pointer xnext.
6
#
Returns: pos_type(off_type(-1) if the positioning operation fails; pos_type(newoff) otherwise.
🔗
pos_type seekpos(pos_type sp, ios_base::openmode which = ios_base::in | ios_base::out) override;
7
#
Effects: Equivalent to: return seekoff(off_type(sp), ios_base::beg, which);
🔗
basic_streambuf<charT, traits>* setbuf(charT* s, streamsize n) override;
8
#
Effects: Equivalent to: this->span(std::span<charT>(s, n)); return this;

31.9.4 Class template basic_ispanstream [ispanstream]

🔗
namespace std { template<class charT, class traits = char_traits<charT>> class basic_ispanstream : public basic_istream<charT, traits> { public: using char_type = charT; using int_type = traits::int_type; using pos_type = traits::pos_type; using off_type = traits::off_type; using traits_type = traits; / [ispanstream.cons], constructors explicit basic_ispanstream(std::span<charT> s, ios_base::openmode which = ios_base::in); basic_ispanstream(const basic_ispanstream&) = delete; basic_ispanstream(basic_ispanstream&& rhs); template<class ROS> explicit basic_ispanstream(ROS&& s); basic_ispanstream& operator=(const basic_ispanstream&) = delete; basic_ispanstream& operator=(basic_ispanstream&& rhs); / [ispanstream.swap], swap void swap(basic_ispanstream& rhs); / [ispanstream.members], member functions basic_spanbuf<charT, traits>* rdbuf() const noexcept; std::span<const charT> span() const noexcept; void span(std::span<charT> s) noexcept; template<class ROS> void span(ROS&& s) noexcept; private: basic_spanbuf<charT, traits> sb; / exposition only }; }
1
#
[Note 1: 
Constructing an ispanstream from a string-literal includes the termination character '\0' in the underlying spanbuf.
— end note]
🔗
explicit basic_ispanstream(std::span<charT> s, ios_base::openmode which = ios_base::in);
1
#
Effects: Initializes the base class with basic_istream<charT, traits>(addressof(sb) and sb with basic_spanbuf<charT, traits>(s, which | ios_base​::​in) ([spanbuf.cons]).
🔗
basic_ispanstream(basic_ispanstream&& rhs);
2
#
Effects: Initializes the base class with std​::​move(rhs) and sb with std​::​move(rhs.sb).
Next, basic_istream<charT, traits>​::​set_rdbuf(addressof(sb) is called to install the contained basic_spanbuf.
🔗
template<class ROS> explicit basic_ispanstream(ROS&& s)
3
#
Constraints: ROS models ranges​::​borrowed_range.
!convertible_to<ROS, std​::​span<charT>> && convertible_to<ROS, std​::​span<charT const> is true.
4
#
Effects: Let sp be std​::​span<const charT>(std​::​forward<ROS>(s)).
Equivalent to: basic_ispanstream(std::span<charT>(const_cast<charT*>(sp.data(), sp.size()
🔗
void swap(basic_ispanstream& rhs);
1
#
Effects: Equivalent to: basic_istream<charT, traits>::swap(rhs); sb.swap(rhs.sb);
🔗
template<class charT, class traits> void swap(basic_ispanstream<charT, traits>& x, basic_ispanstream<charT, traits>& y);
2
#
Effects: Equivalent to x.swap(y).
🔗
basic_spanbuf<charT, traits>* rdbuf() const noexcept;
1
#
Effects: Equivalent to: return const_cast<basic_spanbuf<charT, traits>*>(addressof(sb));
🔗
std::span<const charT> span() const noexcept;
2
#
Effects: Equivalent to: return rdbuf()->span();
🔗
void span(std::span<charT> s) noexcept;
3
#
Effects: Equivalent to rdbuf()->span(s).
🔗
template<class ROS> void span(ROS&& s) noexcept;
4
#
Constraints: ROS models ranges​::​borrowed_range.
(!convertible_to<ROS, std​::​span<charT>>) && convertible_to<ROS, std​::​span<const charT>> is true.
5
#
Effects: Let sp be std​::​span<const charT>(std​::​forward<ROS>(s)).
Equivalent to: this->span(std::span<charT>(const_cast<charT*>(sp.data(), sp.size();

31.9.5 Class template basic_ospanstream [ospanstream]

🔗
namespace std { template<class charT, class traits = char_traits<charT>> class basic_ospanstream : public basic_ostream<charT, traits> { public: using char_type = charT; using int_type = traits::int_type; using pos_type = traits::pos_type; using off_type = traits::off_type; using traits_type = traits; / [ospanstream.cons], constructors explicit basic_ospanstream(std::span<charT> s, ios_base::openmode which = ios_base::out); basic_ospanstream(const basic_ospanstream&) = delete; basic_ospanstream(basic_ospanstream&& rhs); basic_ospanstream& operator=(const basic_ospanstream&) = delete; basic_ospanstream& operator=(basic_ospanstream&& rhs); / [ospanstream.swap], swap void swap(basic_ospanstream& rhs); / [ospanstream.members], member functions basic_spanbuf<charT, traits>* rdbuf() const noexcept; std::span<charT> span() const noexcept; void span(std::span<charT> s) noexcept; private: basic_spanbuf<charT, traits> sb; / exposition only }; }
🔗
explicit basic_ospanstream(std::span<charT> s, ios_base::openmode which = ios_base::out);
1
#
Effects: Initializes the base class with basic_ostream<charT, traits>(addressof(sb) and sb with basic_spanbuf<charT, traits>(s, which | ios_base​::​out) ([spanbuf.cons]).
🔗
basic_ospanstream(basic_ospanstream&& rhs) noexcept;
2
#
Effects: Initializes the base class with std​::​move(rhs) and sb with std​::​move(rhs.sb).
Next, basic_ostream<charT, traits>​::​set_rdbuf(addressof(sb) is called to install the contained basic_spanbuf.
🔗
void swap(basic_ospanstream& rhs);
1
#
Effects: Equivalent to: basic_ostream<charT, traits>::swap(rhs); sb.swap(rhs.sb);
🔗
template<class charT, class traits> void swap(basic_ospanstream<charT, traits>& x, basic_ospanstream<charT, traits>& y);
2
#
Effects: Equivalent to x.swap(y).
🔗
basic_spanbuf<charT, traits>* rdbuf() const noexcept;
1
#
Effects: Equivalent to: return const_cast<basic_spanbuf<charT, traits>*>(addressof(sb));
🔗
std::span<charT> span() const noexcept;
2
#
Effects: Equivalent to: return rdbuf()->span();
🔗
void span(std::span<charT> s) noexcept;
3
#
Effects: Equivalent to rdbuf()->span(s).

31.9.6 Class template basic_spanstream [spanstream]

🔗
namespace std { template<class charT, class traits = char_traits<charT>> class basic_spanstream : public basic_iostream<charT, traits> { public: using char_type = charT; using int_type = traits::int_type; using pos_type = traits::pos_type; using off_type = traits::off_type; using traits_type = traits; / [spanstream.cons], constructors explicit basic_spanstream(std::span<charT> s, ios_base::openmode which = ios_base::out | ios_base::in); basic_spanstream(const basic_spanstream&) = delete; basic_spanstream(basic_spanstream&& rhs); basic_spanstream& operator=(const basic_spanstream&) = delete; basic_spanstream& operator=(basic_spanstream&& rhs); / [spanstream.swap], swap void swap(basic_spanstream& rhs); / [spanstream.members], members basic_spanbuf<charT, traits>* rdbuf() const noexcept; std::span<charT> span() const noexcept; void span(std::span<charT> s) noexcept; private: basic_spanbuf<charT, traits> sb; / exposition only }; }
🔗
explicit basic_spanstream(std::span<charT> s, ios_base::openmode which = ios_base::out | ios_bas::in);
1
#
Effects: Initializes the base class with basic_iostream<charT, traits>(addressof(sb) and sb with basic_spanbuf<charT, traits>(s, which) ([spanbuf.cons]).
🔗
basic_spanstream(basic_spanstream&& rhs);
2
#
Effects: Initializes the base class with std​::​move(rhs) and sb with std​::​move(rhs.sb).
Next, basic_iostream<charT, traits>​::​set_rdbuf(addressof(sb) is called to install the contained basic_spanbuf.
🔗
void swap(basic_spanstream& rhs);
1
#
Effects: Equivalent to: basic_iostream<charT, traits>::swap(rhs); sb.swap(rhs.sb);
🔗
template<class charT, class traits> void swap(basic_spanstream<charT, traits>& x, basic_spanstream<charT, traits>& y);
2
#
Effects: Equivalent to x.swap(y).
🔗
basic_spanbuf<charT, traits>* rdbuf() const noexcept;
1
#
Effects: Equivalent to: return const_cast<basic_spanbuf<charT, traits>*>(addressof(sb));
🔗
std::span<charT> span() const noexcept;
2
#
Effects: Equivalent to: return rdbuf()->span();
🔗
void span(std::span<charT> s) noexcept;
3
#
Effects: Equivalent to rdbuf()->span(s).

31.10 File-based streams [file.streams]

31.10.1 Header <fstream> synopsis [fstream.syn]

🔗
namespace std { / [filebuf], class template basic_filebuf template<class charT, class traits = char_traits<charT>> class basic_filebuf; template<class charT, class traits> void swap(basic_filebuf<charT, traits>& x, basic_filebuf<charT, traits>& y); using filebuf = basic_filebuf<char>; using wfilebuf = basic_filebuf<wchar_t>; / [ifstream], class template basic_ifstream template<class charT, class traits = char_traits<charT>> class basic_ifstream; template<class charT, class traits> void swap(basic_ifstream<charT, traits>& x, basic_ifstream<charT, traits>& y); using ifstream = basic_ifstream<char>; using wifstream = basic_ifstream<wchar_t>; / [ofstream], class template basic_ofstream template<class charT, class traits = char_traits<charT>> class basic_ofstream; template<class charT, class traits> void swap(basic_ofstream<charT, traits>& x, basic_ofstream<charT, traits>& y); using ofstream = basic_ofstream<char>; using wofstream = basic_ofstream<wchar_t>; / [fstream], class template basic_fstream template<class charT, class traits = char_traits<charT>> class basic_fstream; template<class charT, class traits> void swap(basic_fstream<charT, traits>& x, basic_fstream<charT, traits>& y); using fstream = basic_fstream<char>; using wfstream = basic_fstream<wchar_t>; }
1
#
The header <fstream> defines four class templates and eight types that associate stream buffers with files and assist reading and writing files.
2
#
[Note 1: 
The class template basic_filebuf treats a file as a source or sink of bytes.
In an environment that uses a large character set, the file typically holds multibyte character sequences and the basic_filebuf object converts those multibyte sequences into wide character sequences.
— end note]
3
#
In subclause [file.streams], member functions taking arguments of const filesystem​::​path​::​value_type* are only provided on systems where filesystem​::​path​::​value_type ([fs.class.path]) is not char.
[Note 2: 
These functions enable class path support for systems with a wide native path character type, such as wchar_t.
— end note]

31.10.2 Native handles [file.native]

1
#
Several classes described in [file.streams] have a member native_handle_type.
2
#
The type native_handle_type represents a platform-specific native handle to a file.
It is trivially copyable and models semiregular.
[Note 1: 
For operating systems based on POSIX, native_handle_type is int.
For Windows-based operating systems, native_handle_type is HANDLE.
— end note]

31.10.3 Class template basic_filebuf [filebuf]

🔗
namespace std { template<class charT, class traits = char_traits<charT>> class basic_filebuf : public basic_streambuf<charT, traits> { public: using char_type = charT; using int_type = traits::int_type; using pos_type = traits::pos_type; using off_type = traits::off_type; using traits_type = traits; using native_handle_type = implementation-defined; / see [file.native] / [filebuf.cons], constructors/destructor basic_filebuf(); basic_filebuf(const basic_filebuf&) = delete; basic_filebuf(basic_filebuf&& rhs); virtual ~basic_filebuf(); / [filebuf.assign], assignment and swap basic_filebuf& operator=(const basic_filebuf&) = delete; basic_filebuf& operator=(basic_filebuf&& rhs); void swap(basic_filebuf& rhs); / [filebuf.members], members bool is_open() const; basic_filebuf* open(const char* s, ios_base::openmode mode); basic_filebuf* open(const filesystem::path::value_type* s, ios_base::openmode mode); / wide systems only; see [fstream.syn] basic_filebuf* open(const string& s, ios_base::openmode mode); basic_filebuf* open(const filesystem::path& s, ios_base::openmode mode); basic_filebuf* close(); native_handle_type native_handle() const noexcept; protected: / [filebuf.virtuals], overridden virtual functions streamsize showmanyc() override; int_type underflow() override; int_type uflow() override; int_type pbackfail(int_type c = traits::eof() override; int_type overflow (int_type c = traits::eof() override; basic_streambuf<charT, traits>* setbuf(char_type* s, streamsize n) override; pos_type seekoff(off_type off, ios_base::seekdir way, ios_base::openmode which = ios_base::in | ios_base::out) override; pos_type seekpos(pos_type sp, ios_base::openmode which = ios_base::in | ios_base::out) override; int sync() override; void imbue(const locale& loc) override; }; }
1
#
The class basic_filebuf<charT, traits> associates both the input sequence and the output sequence with a file.
2
#
The restrictions on reading and writing a sequence controlled by an object of class basic_filebuf<charT, traits> are the same as for reading and writing with the C standard library FILEs.
3
#
In particular:
  • (3.1)
    If the file is not open for reading the input sequence cannot be read.
  • (3.2)
    If the file is not open for writing the output sequence cannot be written.
  • (3.3)
    A joint file position is maintained for both the input sequence and the output sequence.
4
#
An instance of basic_filebuf behaves as described in [filebuf] provided traits​::​pos_type is fpos<traits​::​​state_type>.
Otherwise the behavior is undefined.
5
#
The file associated with a basic_filebuf has an associated value of type native_handle_type, called the native handle ([file.native]) of that file.
This native handle can be obtained by calling the member function native_handle.
6
#
For any opened basic_filebuf f, the native handle returned by f.native_handle() is invalidated when f.close() is called, or f is destroyed.
7
#
In order to support file I/O and multibyte/wide character conversion, conversions are performed using members of a facet, referred to as a_codecvt in following subclauses, obtained as if by const codecvt<charT, char, typename traits::state_type>& a_codecvt = use_facet<codecvt<charT, char, typename traits::state_type>>(getloc();
🔗
basic_filebuf();
1
#
Effects: Initializes the base class with basic_streambuf<charT, traits>() ([streambuf.cons]).
2
#
Postconditions: is_open() == false.
🔗
basic_filebuf(basic_filebuf&& rhs);
3
#
Effects: It is implementation-defined whether the sequence pointers in *this (eback(), gptr(), egptr(), pbase(), pptr(), epptr()) obtain the values which rhs had.
Whether they do or not, *this and rhs reference separate buffers (if any at all) after the construction.
Additionally *this references the file which rhs did before the construction, and rhs references no file after the construction.
The openmode, locale and any other state of rhs is also copied.
4
#
Postconditions: Let rhs_p refer to the state of rhs just prior to this construction and let rhs_a refer to the state of rhs just after this construction.
  • (4.1)
    is_open() == rhs_p.is_open()
  • (4.2)
    rhs_a.is_open() == false
  • (4.3)
    gptr() - eback() == rhs_p.gptr() - rhs_p.eback()
  • (4.4)
    egptr() - eback() == rhs_p.egptr() - rhs_p.eback()
  • (4.5)
    pptr() - pbase() == rhs_p.pptr() - rhs_p.pbase()
  • (4.6)
    epptr() - pbase() == rhs_p.epptr() - rhs_p.pbase()
  • (4.7)
    if (eback() eback() != rhs_a.eback()
  • (4.8)
    if (gptr() gptr() != rhs_a.gptr()
  • (4.9)
    if (egptr() egptr() != rhs_a.egptr()
  • (4.10)
    if (pbase() pbase() != rhs_a.pbase()
  • (4.11)
    if (pptr() pptr() != rhs_a.pptr()
  • (4.12)
    if (epptr() epptr() != rhs_a.epptr()
🔗
virtual ~basic_filebuf();
5
#
Effects: Calls close().
If an exception occurs during the destruction of the object, including the call to close(), the exception is caught but not rethrown (see [res.on.exception.handling]).

31.10.3.3 Assignment and swap [filebuf.assign]

🔗
basic_filebuf& operator=(basic_filebuf&& rhs);
1
#
Effects: Calls close() then move assigns from rhs.
After the move assignment *this has the observable state it would have had if it had been move constructed from rhs (see [filebuf.cons]).
2
#
Returns: *this.
🔗
void swap(basic_filebuf& rhs);
3
#
Effects: Exchanges the state of *this and rhs.
🔗
template<class charT, class traits> void swap(basic_filebuf<charT, traits>& x, basic_filebuf<charT, traits>& y);
4
#
Effects: Equivalent to x.swap(y).

31.10.3.4 Member functions [filebuf.members]

🔗
bool is_open() const;
1
#
Returns: true if a previous call to open succeeded (returned a non-null value) and there has been no intervening call to close.
🔗
basic_filebuf* open(const char* s, ios_base::openmode mode); basic_filebuf* open(const filesystem::path::value_type* s, ios_base::openmode mode); / wide systems only; see [fstream.syn]
2
#
Effects: If is_open() != false, returns a null pointer.
Otherwise, initializes the filebuf as required.
It then opens the file to which s resolves, if possible, as if by a call to fopen with the second argument determined from mode & ~ios_base​::​ate as indicated in Table 146.
If mode is not some combination of flags shown in the table then the open fails.
Table 146 — File open modes [tab:filebuf.open.modes]
🔗
ios_base flag combination
stdio equivalent
🔗
binary
in
out
trunc
app
noreplace
🔗
+
"w"
🔗
+
+
"wx"
🔗
+
+
"w"
🔗
+
+
+
"wx"
🔗
+
+
"a"
🔗
+
"a"
🔗
+
"r"
🔗
+
+
"r+"
🔗
+
+
+
"w+"
🔗
+
+
+
+
"w+x"
🔗
+
+
+
"a+"
🔗
+
+
"a+"
🔗
+
+
"wb"
🔗
+
+
+
"wbx"
🔗
+
+
+
"wb"
🔗
+
+
+
+
"wbx"
🔗
+
+
+
"ab"
🔗
+
+
"ab"
🔗
+
+
"rb"
🔗
+
+
+
"r+b"
🔗
+
+
+
+
"w+b"
🔗
+
+
+
+
+
"w+bx"
🔗
+
+
+
+
"a+b"
🔗
+
+
+
"a+b"
4
#
If the open operation succeeds and ios_base​::​ate is set in mode, positions the file to the end (as if by calling fseek(file, 0, SEEK_END), where file is the pointer returned by calling fopen).284
5
#
If the repositioning operation fails, calls close() and returns a null pointer to indicate failure.
6
#
Returns: this if successful, a null pointer otherwise.
🔗
basic_filebuf* open(const string& s, ios_base::openmode mode); basic_filebuf* open(const filesystem::path& s, ios_base::openmode mode);
7
#
Returns: open(s.c_str(), mode);
🔗
basic_filebuf* close();
8
#
Effects: If is_open() == false, returns a null pointer.
If a put area exists, calls overflow(traits​::​​eof() to flush characters.
If the last virtual member function called on *this (between underflow, overflow, seekoff, and seekpos) was overflow then calls a_codecvt.unshift (possibly several times) to determine a termination sequence, inserts those characters and calls overflow(traits​::​​eof() again.
Finally, regardless of whether any of the preceding calls fails or throws an exception, the function closes the file (as if by calling fclose(file)).
If any of the calls made by the function, including fclose, fails, close fails by returning a null pointer.
If one of these calls throws an exception, the exception is caught and rethrown after closing the file.
9
#
Returns: this on success, a null pointer otherwise.
🔗
native_handle_type native_handle() const noexcept;
11
#
Returns: The native handle associated with *this.
284)284)
The macro SEEK_END is defined, and the function signatures fopen(const char*, const char*) and fseek(FILE*, long, int) are declared, in <cstdio>.

31.10.3.5 Overridden virtual functions [filebuf.virtuals]

🔗
streamsize showmanyc() override;
1
#
Effects: Behaves the same as basic_streambuf​::​showmanyc() ([streambuf.virtuals]).
2
#
Remarks: An implementation may provide an overriding definition for this function signature if it can determine whether more characters can be read from the input sequence.
🔗
int_type underflow() override;
3
#
Effects: Behaves according to the description of basic_streambuf<charT, traits>​::​underflow(), with the specialization that a sequence of characters is read from the input sequence as if by reading from the associated file into an internal buffer (extern_buf) and then as if by doing: char extern_buf[XSIZE]; const char* extern_end; charT intern_buf[ISIZE]; charT* intern_end; codecvt_base::result r = a_codecvt.in(state, extern_buf, extern_buf+XSIZE, extern_end, intern_buf, intern_buf+ISIZE, intern_end);
This shall be done in such a way that the class can recover the position (fpos_t) corresponding to each character between intern_buf and intern_end.
If the value of r indicates that a_codecvt.in() ran out of space in intern_buf, retry with a larger intern_buf.
🔗
int_type uflow() override;
4
#
Effects: Behaves according to the description of basic_streambuf<charT, traits>​::​uflow(), with the specialization that a sequence of characters is read from the input with the same method as used by underflow.
🔗
int_type pbackfail(int_type c = traits::eof() override;
5
#
Effects: Puts back the character designated by c to the input sequence, if possible, in one of three ways:
  • (5.1)
    If traits​::​eq_int_type(c, traits​::​eof() returns false and if the function makes a putback position available and if traits​::​eq(to_char_type(c), gptr()[-1]) returns true, decrements the next pointer for the input sequence, gptr().
    Returns: c.
  • (5.2)
    If traits​::​eq_int_type(c, traits​::​eof() returns false and if the function makes a putback position available and if the function is permitted to assign to the putback position, decrements the next pointer for the input sequence, and stores c there.
    Returns: c.
  • (5.3)
    If traits​::​eq_int_type(c, traits​::​eof() returns true, and if either the input sequence has a putback position available or the function makes a putback position available, decrements the next pointer for the input sequence, gptr().
    Returns: traits​::​not_eof(c).
6
#
Returns: As specified above, or traits​::​eof() to indicate failure.
7
#
Remarks: If is_open() == false, the function always fails.
8
#
If the function can succeed in more than one of these ways, it is unspecified which way is chosen.
The function can alter the number of putback positions available as a result of any call.
🔗
int_type overflow(int_type c = traits::eof() override;
10
#
Effects: Behaves according to the description of basic_streambuf<charT, traits>​::​overflow(c), except that the behavior of “consuming characters” is performed by first converting as if by: charT* b = pbase(); charT* p = pptr(); const charT* end; char xbuf[XSIZE]; char* xbuf_end; codecvt_base::result r = a_codecvt.out(state, b, p, end, xbuf, xbuf+XSIZE, xbuf_end); and then
  • (10.1)
    If r == codecvt_base​::​error then fail.
  • (10.2)
    If r == codecvt_base​::​noconv then output characters from b up to (and not including) p.
  • (10.3)
    If r == codecvt_base​::​partial then output to the file characters from xbuf up to xbuf_end, and repeat using characters from end to p.
    If output fails, fail (without repeating).
  • (10.4)
    Otherwise output from xbuf to xbuf_end, and fail if output fails.
    At this point if b != p and b == end (xbuf isn't large enough) then increase XSIZE and repeat from the beginning.
Then establishes an observable checkpoint ([intro.abstract]).
11
#
Returns: traits​::​not_eof(c) to indicate success, and traits​::​eof() to indicate failure.
If is_open() == false, the function always fails.
🔗
basic_streambuf* setbuf(char_type* s, streamsize n) override;
12
#
Effects: If setbuf(0, 0) is called on a stream before any I/O has occurred on that stream, the stream becomes unbuffered.
Otherwise the results are implementation-defined.
“Unbuffered” means that pbase() and pptr() always return null and output to the file should appear as soon as possible.
🔗
pos_type seekoff(off_type off, ios_base::seekdir way, ios_base::openmode which = ios_base::in | ios_base::out) override;
13
#
Effects: Let width denote a_codecvt.encoding().
If is_open() == false, or off != 0 && width <= 0, then the positioning operation fails.
Otherwise, if way != basic_ios​::​cur or off != 0, and if the last operation was output, then update the output sequence and write any unshift sequence.
Next, seek to the new position: if width > 0, call fseek(file, width * off, whence), otherwise call fseek(file, 0, whence).
14
#
Returns: A newly constructed pos_type object that stores the resultant stream position, if possible.
If the positioning operation fails, or if the object cannot represent the resultant stream position, returns pos_type(off_type(-1).
15
#
Remarks: “The last operation was output” means either the last virtual operation was overflow or the put buffer is non-empty.
“Write any unshift sequence” means, if width is less than zero then call a_codecvt.unshift(state, xbuf, xbuf+XSIZE, xbuf_end) and output the resulting unshift sequence.
The function determines one of three values for the argument whence, of type int, as indicated in Table 147.
Table 147 — seekoff effects [tab:filebuf.seekoff]
🔗
way Value
stdio Equivalent
🔗
basic_ios​::​beg
SEEK_SET
🔗
basic_ios​::​cur
SEEK_CUR
🔗
basic_ios​::​end
SEEK_END
🔗
pos_type seekpos(pos_type sp, ios_base::openmode which = ios_base::in | ios_base::out) override;
16
#
Alters the file position, if possible, to correspond to the position stored in sp (as described below).
Altering the file position performs as follows:
1.if (om & ios_base​::​out) != 0, then update the output sequence and write any unshift sequence;
2.set the file position to sp as if by a call to fsetpos;
3.if (om & ios_base​::​in) != 0, then update the input sequence;
where om is the open mode passed to the last call to open().
The operation fails if is_open() returns false.
17
#
If sp is an invalid stream position, or if the function positions neither sequence, the positioning operation fails.
If sp has not been obtained by a previous successful call to one of the positioning functions (seekoff or seekpos) on the same file the effects are undefined.
18
#
Returns: sp on success.
Otherwise returns pos_type(off_type(-1).
🔗
int sync() override;
19
#
Effects: If a put area exists, calls filebuf​::​overflow to write the characters to the file, then flushes the file as if by calling fflush(file).
If a get area exists, the effect is implementation-defined.
🔗
void imbue(const locale& loc) override;
20
#
Preconditions: If the file is not positioned at its beginning and the encoding of the current locale as determined by a_codecvt.encoding() is state-dependent ([locale.codecvt.virtuals]) then that facet is the same as the corresponding facet of loc.
21
#
Effects: Causes characters inserted or extracted after this call to be converted according to loc until another call of imbue.
22
#
Remarks: This may require reconversion of previously converted characters.
This in turn may require the implementation to be able to reconstruct the original contents of the file.

31.10.4 Class template basic_ifstream [ifstream]

🔗
namespace std { template<class charT, class traits = char_traits<charT>> class basic_ifstream : public basic_istream<charT, traits> { public: using char_type = charT; using int_type = traits::int_type; using pos_type = traits::pos_type; using off_type = traits::off_type; using traits_type = traits; using native_handle_type = basic_filebuf<charT, traits>::native_handle_type; / [ifstream.cons], constructors basic_ifstream(); explicit basic_ifstream(const char* s, ios_base::openmode mode = ios_base::in); explicit basic_ifstream(const filesystem::path::value_type* s, ios_base::openmode mode = ios_base::in);/ wide systems only; see [fstream.syn] explicit basic_ifstream(const string& s, ios_base::openmode mode = ios_base::in); template<class T> explicit basic_ifstream(const T& s, ios_base::openmode mode = ios_base::in); basic_ifstream(const basic_ifstream&) = delete; basic_ifstream(basic_ifstream&& rhs); basic_ifstream& operator=(const basic_ifstream&) = delete; basic_ifstream& operator=(basic_ifstream&& rhs); / [ifstream.swap], swap void swap(basic_ifstream& rhs); / [ifstream.members], members basic_filebuf<charT, traits>* rdbuf() const; native_handle_type native_handle() const noexcept; bool is_open() const; void open(const char* s, ios_base::openmode mode = ios_base::in); void open(const filesystem::path::value_type* s, ios_base::openmode mode = ios_base::in); / wide systems only; see [fstream.syn] void open(const string& s, ios_base::openmode mode = ios_base::in); void open(const filesystem::path& s, ios_base::openmode mode = ios_base::in); void close(); private: basic_filebuf<charT, traits> sb; / exposition only }; }
1
#
The class basic_ifstream<charT, traits> supports reading from named files.
It uses a basic_filebuf<​charT, traits> object to control the associated sequence.
For the sake of exposition, the maintained data is presented here as:
🔗
basic_ifstream();
1
#
Effects: Initializes the base class with basic_istream<charT, traits>(addressof(sb) ([istream.cons]) and sb with basic_filebuf<charT, traits>() ([filebuf.cons]).
🔗
explicit basic_ifstream(const char* s, ios_base::openmode mode = ios_base::in); explicit basic_ifstream(const filesystem::path::value_type* s, ios_base::openmode mode = ios_base::in); / wide systems only; see [fstream.syn]
2
#
Effects: Initializes the base class with basic_istream<charT, traits>(addressof(sb) ([istream.cons]) and sb with basic_filebuf<charT, traits>() ([filebuf.cons]), then calls rdbuf()->open(s, mode | ios_base​::​in).
If that function returns a null pointer, calls setstate(failbit).
🔗
explicit basic_ifstream(const string& s, ios_base::openmode mode = ios_base::in);
3
#
Effects: Equivalent to basic_ifstream(s.c_str(), mode).
🔗
template<class T> explicit basic_ifstream(const T& s, ios_base::openmode mode = ios_base::in);
4
#
Effects: Equivalent to basic_ifstream(s.c_str(), mode).
🔗
basic_ifstream(basic_ifstream&& rhs);
6
#
Effects: Move constructs the base class, and the contained basic_filebuf.
Then calls basic_istream<charT, traits>​::​set_rdbuf(​addressof(sb) to install the contained basic_filebuf.
🔗
void swap(basic_ifstream& rhs);
1
#
Effects: Exchanges the state of *this and rhs by calling basic_istream<charT, traits>​::​swap(rhs) and sb.swap(rhs.sb).
🔗
template<class charT, class traits> void swap(basic_ifstream<charT, traits>& x, basic_ifstream<charT, traits>& y);
2
#
Effects: Equivalent to x.swap(y).

31.10.4.4 Member functions [ifstream.members]

🔗
basic_filebuf<charT, traits>* rdbuf() const;
1
#
Returns: const_cast<basic_filebuf<charT, traits>*>(addressof(sb).
🔗
native_handle_type native_handle() const noexcept;
2
#
Effects: Equivalent to: return rdbuf()->native_handle();
🔗
bool is_open() const;
3
#
Returns: rdbuf()->is_open().
🔗
void open(const char* s, ios_base::openmode mode = ios_base::in); void open(const filesystem::path::value_type* s, ios_base::openmode mode = ios_base::in); / wide systems only; see [fstream.syn]
4
#
Effects: Calls rdbuf()->open(s, mode | ios_base​::​in).
If that function does not return a null pointer calls clear(), otherwise calls setstate(failbit) (which may throw ios_base​::​failure) ([iostate.flags]).
🔗
void open(const string& s, ios_base::openmode mode = ios_base::in); void open(const filesystem::path& s, ios_base::openmode mode = ios_base::in);
5
#
Effects: Calls open(s.c_str(), mode).
🔗
void close();
6
#
Effects: Calls rdbuf()->close() and, if that function returns a null pointer, calls setstate(failbit) (which may throw ios_base​::​failure) ([iostate.flags]).

31.10.5 Class template basic_ofstream [ofstream]

🔗
namespace std { template<class charT, class traits = char_traits<charT>> class basic_ofstream : public basic_ostream<charT, traits> { public: using char_type = charT; using int_type = traits::int_type; using pos_type = traits::pos_type; using off_type = traits::off_type; using traits_type = traits; using native_handle_type = basic_filebuf<charT, traits>::native_handle_type; / [ofstream.cons], constructors basic_ofstream(); explicit basic_ofstream(const char* s, ios_base::openmode mode = ios_base::out); explicit basic_ofstream(const filesystem::path::value_type* s, / wide systems only; see [fstream.syn] ios_base::openmode mode = ios_base::out); explicit basic_ofstream(const string& s, ios_base::openmode mode = ios_base::out); template<class T> explicit basic_ofstream(const T& s, ios_base::openmode mode = ios_base::out); basic_ofstream(const basic_ofstream&) = delete; basic_ofstream(basic_ofstream&& rhs); basic_ofstream& operator=(const basic_ofstream&) = delete; basic_ofstream& operator=(basic_ofstream&& rhs); / [ofstream.swap], swap void swap(basic_ofstream& rhs); / [ofstream.members], members basic_filebuf<charT, traits>* rdbuf() const; native_handle_type native_handle() const noexcept; bool is_open() const; void open(const char* s, ios_base::openmode mode = ios_base::out); void open(const filesystem::path::value_type* s, ios_base::openmode mode = ios_base::out); / wide systems only; see [fstream.syn] void open(const string& s, ios_base::openmode mode = ios_base::out); void open(const filesystem::path& s, ios_base::openmode mode = ios_base::out); void close(); private: basic_filebuf<charT, traits> sb; / exposition only }; }
1
#
The class basic_ofstream<charT, traits> supports writing to named files.
It uses a basic_filebuf<​charT, traits> object to control the associated sequence.
For the sake of exposition, the maintained data is presented here as:
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basic_ofstream();
1
#
Effects: Initializes the base class with basic_ostream<charT, traits>(addressof(sb) ([ostream.cons]) and sb with basic_filebuf<charT, traits>() ([filebuf.cons]).
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explicit basic_ofstream(const char* s, ios_base::openmode mode = ios_base::out); explicit basic_ofstream(const filesystem::path::value_type* s, ios_base::openmode mode = ios_base::out); / wide systems only; see [fstream.syn]
2
#
Effects: Initializes the base class with basic_ostream<charT, traits>(addressof(sb) ([ostream.cons]) and sb with basic_filebuf<charT, traits>() ([filebuf.cons]), then calls rdbuf()->open(s, mode | ios_base​::​out).
If that function returns a null pointer, calls setstate(​failbit).
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explicit basic_ofstream(const string& s, ios_base::openmode mode = ios_base::out);
3
#
Effects: Equivalent to basic_ofstream(s.c_str(), mode).
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template<class T> explicit basic_ofstream(const T& s, ios_base::openmode mode = ios_base::out);
4
#
Effects: Equivalent to basic_ofstream(s.c_str(), mode).
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basic_ofstream(basic_ofstream&& rhs);
6
#
Effects: Move constructs the base class, and the contained basic_filebuf.
Then calls basic_ostream<charT, traits>​::​set_rdbuf(​addressof(sb) to install the contained basic_filebuf.
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void swap(basic_ofstream& rhs);
1
#
Effects: Exchanges the state of *this and rhs by calling basic_ostream<charT, traits>​::​swap(rhs) and sb.swap(rhs.sb).
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template<class charT, class traits> void swap(basic_ofstream<charT, traits>& x, basic_ofstream<charT, traits>& y);
2
#
Effects: Equivalent to x.swap(y).

31.10.5.4 Member functions [ofstream.members]

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basic_filebuf<charT, traits>* rdbuf() const;
1
#
Returns: const_cast<basic_filebuf<charT, traits>*>(addressof(sb).
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native_handle_type native_handle() const noexcept;
2
#
Effects: Equivalent to: return rdbuf()->native_handle();
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bool is_open() const;
3
#
Returns: rdbuf()->is_open().
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void open(const char* s, ios_base::openmode mode = ios_base::out); void open(const filesystem::path::value_type* s, ios_base::openmode mode = ios_base::out); / wide systems only; see [fstream.syn]
4
#
Effects: Calls rdbuf()->open(s, mode | ios_base​::​out).
If that function does not return a null pointer calls clear(), otherwise calls setstate(​failbit) (which may throw ios_base​::​failure) ([iostate.flags]).
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void close();
5
#
Effects: Calls rdbuf()->close() and, if that function fails (returns a null pointer), calls setstate(​failbit) (which may throw ios_base​::​failure) ([iostate.flags]).
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void open(const string& s, ios_base::openmode mode = ios_base::out); void open(const filesystem::path& s, ios_base::openmode mode = ios_base::out);
6
#
Effects: Calls open(s.c_str(), mode).

31.10.6 Class template basic_fstream [fstream]

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namespace std { template<class charT, class traits = char_traits<charT>> class basic_fstream : public basic_iostream<charT, traits> { public: using char_type = charT; using int_type = traits::int_type; using pos_type = traits::pos_type; using off_type = traits::off_type; using traits_type = traits; using native_handle_type = basic_filebuf<charT, traits>::native_handle_type; / [fstream.cons], constructors basic_fstream(); explicit basic_fstream( const char* s, ios_base::openmode mode = ios_base::in | ios_base::out); explicit basic_fstream( const filesystem::path::value_type* s, ios_base::openmode mode = ios_base::in | ios_base::out); / wide systems only; see [fstream.syn] explicit basic_fstream( const string& s, ios_base::openmode mode = ios_base::in | ios_base::out); template<class T> explicit basic_fstream(const T& s, ios_base::openmode mode = ios_base::in | ios_base::out); basic_fstream(const basic_fstream&) = delete; basic_fstream(basic_fstream&& rhs); basic_fstream& operator=(const basic_fstream&) = delete; basic_fstream& operator=(basic_fstream&& rhs); / [fstream.swap], swap void swap(basic_fstream& rhs); / [fstream.members], members basic_filebuf<charT, traits>* rdbuf() const; native_handle_type native_handle() const noexcept; bool is_open() const; void open( const char* s, ios_base::openmode mode = ios_base::in | ios_base::out); void open( const filesystem::path::value_type* s, ios_base::openmode mode = ios_base::in | ios_base::out); / wide systems only; see [fstream.syn] void open( const string& s, ios_base::openmode mode = ios_base::in | ios_base::out); void open( const filesystem::path& s, ios_base::openmode mode = ios_base::in | ios_base::out); void close(); private: basic_filebuf<charT, traits> sb; / exposition only }; }
1
#
The class template basic_fstream<charT, traits> supports reading and writing from named files.
It uses a basic_filebuf<charT, traits> object to control the associated sequences.
For the sake of exposition, the maintained data is presented here as:
  • (1.1)
    sb, the basic_filebuf object.
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basic_fstream();
1
#
Effects: Initializes the base class with basic_iostream<charT, traits>(addressof(sb) ([iostream.cons]) and sb with basic_filebuf<charT, traits>().
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explicit basic_fstream( const char* s, ios_base::openmode mode = ios_base::in | ios_base::out); explicit basic_fstream( const filesystem::path::value_type* s, ios_base::openmode mode = ios_base::in | ios_base::out); / wide systems only; see [fstream.syn]
2
#
Effects: Initializes the base class with basic_iostream<charT, traits>(addressof(sb) ([iostream.cons]) and sb with basic_filebuf<charT, traits>().
Then calls rdbuf()->open(s, mode).
If that function returns a null pointer, calls setstate(failbit).
🔗
explicit basic_fstream( const string& s, ios_base::openmode mode = ios_base::in | ios_base::out);
3
#
Effects: Equivalent to basic_fstream(s.c_str(), mode).
🔗
template<class T> explicit basic_fstream(const T& s, ios_base::openmode mode = ios_base::in | ios_base::out);
4
#
Effects: Equivalent to basic_fstream(s.c_str(), mode).
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basic_fstream(basic_fstream&& rhs);
6
#
Effects: Move constructs the base class, and the contained basic_filebuf.
Then calls basic_istream<charT, traits>​::​set_rdbuf(​addressof(sb) to install the contained basic_filebuf.
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void swap(basic_fstream& rhs);
1
#
Effects: Exchanges the state of *this and rhs by calling basic_iostream<charT,traits>​::​swap(rhs) and sb.swap(rhs.sb).
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template<class charT, class traits> void swap(basic_fstream<charT, traits>& x, basic_fstream<charT, traits>& y);
2
#
Effects: Equivalent to x.swap(y).

31.10.6.4 Member functions [fstream.members]

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basic_filebuf<charT, traits>* rdbuf() const;
1
#
Returns: const_cast<basic_filebuf<charT, traits>*>(addressof(sb).
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native_handle_type native_handle() const noexcept;
2
#
Effects: Equivalent to: return rdbuf()->native_handle();
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bool is_open() const;
3
#
Returns: rdbuf()->is_open().
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void open( const char* s, ios_base::openmode mode = ios_base::in | ios_base::out); void open( const filesystem::path::value_type* s, ios_base::openmode mode = ios_base::in | ios_base::out); / wide systems only; see [fstream.syn]
4
#
Effects: Calls rdbuf()->open(s, mode).
If that function does not return a null pointer calls clear(), otherwise calls setstate(failbit) (which may throw ios_base​::​failure) ([iostate.flags]).
🔗
void open( const string& s, ios_base::openmode mode = ios_base::in | ios_base::out); void open( const filesystem::path& s, ios_base::openmode mode = ios_base::in | ios_base::out);
5
#
Effects: Calls open(s.c_str(), mode).
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void close();
6
#
Effects: Calls rdbuf()->close() and, if that function returns a null pointer, calls setstate(failbit) (which may throw ios_base​::​failure) ([iostate.flags]).

31.11 Synchronized output streams [syncstream]

31.11.1 Header <syncstream> synopsis [syncstream.syn]

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#include <ostream> / see [ostream.syn] namespace std { / [syncstream.syncbuf], class template basic_syncbuf template<class charT, class traits = char_traits<charT>, class Allocator = allocator<charT>> class basic_syncbuf; / [syncstream.syncbuf.special], specialized algorithms template<class charT, class traits, class Allocator> void swap(basic_syncbuf<charT, traits, Allocator>&, basic_syncbuf<charT, traits, Allocator>&); using syncbuf = basic_syncbuf<char>; using wsyncbuf = basic_syncbuf<wchar_t>; / [syncstream.osyncstream], class template basic_osyncstream template<class charT, class traits = char_traits<charT>, class Allocator = allocator<charT>> class basic_osyncstream; using osyncstream = basic_osyncstream<char>; using wosyncstream = basic_osyncstream<wchar_t>; }
1
#
The header <syncstream> provides a mechanism to synchronize execution agents writing to the same stream.

31.11.2 Class template basic_syncbuf [syncstream.syncbuf]

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namespace std { template<class charT, class traits = char_traits<charT>, class Allocator = allocator<charT>> class basic_syncbuf : public basic_streambuf<charT, traits> { public: using char_type = charT; using int_type = traits::int_type; using pos_type = traits::pos_type; using off_type = traits::off_type; using traits_type = traits; using allocator_type = Allocator; using streambuf_type = basic_streambuf<charT, traits>; / [syncstream.syncbuf.cons], construction and destruction basic_syncbuf() : basic_syncbuf(nullptr) {} explicit basic_syncbuf(streambuf_type* obuf) : basic_syncbuf(obuf, Allocator() {} basic_syncbuf(streambuf_type*, const Allocator&); basic_syncbuf(basic_syncbuf&&); ~basic_syncbuf(); / [syncstream.syncbuf.assign], assignment and swap basic_syncbuf& operator=(basic_syncbuf&&); void swap(basic_syncbuf&); / [syncstream.syncbuf.members], member functions bool emit(); streambuf_type* get_wrapped() const noexcept; allocator_type get_allocator() const noexcept; void set_emit_on_sync(bool) noexcept; protected: / [syncstream.syncbuf.virtuals], overridden virtual functions int sync() override; private: streambuf_type* wrapped; / exposition only bool emit-on-sync{}; / exposition only }; }
1
#
Class template basic_syncbuf stores character data written to it, known as the associated output, into internal buffers allocated using the object's allocator.
The associated output is transferred to the wrapped stream buffer object *wrapped when emit() is called or when the basic_syncbuf object is destroyed.
Such transfers are atomic with respect to transfers by other basic_syncbuf objects with the same wrapped stream buffer object.

31.11.2.2 Construction and destruction [syncstream.syncbuf.cons]

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basic_syncbuf(streambuf_type* obuf, const Allocator& allocator);
1
#
Postconditions: get_wrapped() == obuf and get_allocator() == allocator are true.
3
#
Throws: Nothing unless an exception is thrown by the construction of a mutex or by memory allocation.
4
#
Remarks: A copy of allocator is used to allocate memory for internal buffers holding the associated output.
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basic_syncbuf(basic_syncbuf&& other);
5
#
Postconditions: The value returned by this->get_wrapped() is the value returned by other.get_wrapped() prior to calling this constructor.
Output stored in other prior to calling this constructor will be stored in *this afterwards.
other.pbase() == other.pptr() and other.get_wrapped() == nullptr are true.
6
#
Remarks: This constructor disassociates other from its wrapped stream buffer, ensuring destruction of other produces no output.
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~basic_syncbuf();
7
#
Throws: Nothing.
If an exception is thrown from emit(), the destructor catches and ignores that exception.
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basic_syncbuf& operator=(basic_syncbuf&& rhs);
1
#
Effects: Calls emit() then move assigns from rhs.
After the move assignment *this has the observable state it would have had if it had been move constructed from rhs ([syncstream.syncbuf.cons]).
2
#
Postconditions:
  • (2.1)
    rhs.get_wrapped() == nullptr is true.
  • (2.2)
    this->get_allocator() == rhs.get_allocator() is true when allocator_traits<Allocator>::propagate_on_container_move_assignment::value is true; otherwise, the allocator is unchanged.
3
#
Remarks: This assignment operator disassociates rhs from its wrapped stream buffer, ensuring destruction of rhs produces no output.
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void swap(basic_syncbuf& other);
5
#
Preconditions: Either allocator_traits<Allocator>​::​propagate_on_container_swap​::​value is true or this->get_allocator() == other.get_allocator() is true.
6
#
Effects: Exchanges the state of *this and other.
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bool emit();
1
#
Effects: Atomically transfers the associated output of *this to the stream buffer *wrapped, so that it appears in the output stream as a contiguous sequence of characters.
wrapped->pubsync() is called if and only if a call was made to sync() since the most recent call to emit(), if any.
2
#
Synchronization: All emit() calls transferring characters to the same stream buffer object appear to execute in a total order consistent with the “happens before” relation ([intro.races]), where each emit() call synchronizes with subsequent emit() calls in that total order.
3
#
Returns: true if all of the following conditions hold; otherwise false:
  • (4.1)
    wrapped == nullptr is false.
  • (4.2)
    All of the characters in the associated output were successfully transferred.
  • (4.3)
    The call to wrapped->pubsync() (if any) succeeded.
5
#
Remarks: May call member functions of wrapped while holding a lock uniquely associated with wrapped.
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streambuf_type* get_wrapped() const noexcept;
6
#
Returns: wrapped.
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allocator_type get_allocator() const noexcept;
7
#
Returns: A copy of the allocator that was set in the constructor or assignment operator.
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void set_emit_on_sync(bool b) noexcept;
8
#
Effects: emit-on-sync = b.

31.11.2.5 Overridden virtual functions [syncstream.syncbuf.virtuals]

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int sync() override;
1
#
Effects: Records that the wrapped stream buffer is to be flushed.
Then, if emit-on-sync is true, calls emit().
[Note 1: 
If emit-on-sync is false, the actual flush is delayed until a call to emit().
— end note]
2
#
Returns: If emit() was called and returned false, returns -1; otherwise 0.
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template<class charT, class traits, class Allocator> void swap(basic_syncbuf<charT, traits, Allocator>& a, basic_syncbuf<charT, traits, Allocator>& b);
1
#
Effects: Equivalent to a.swap(b).

31.11.3 Class template basic_osyncstream [syncstream.osyncstream]

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namespace std { template<class charT, class traits = char_traits<charT>, class Allocator = allocator<charT>> class basic_osyncstream : public basic_ostream<charT, traits> { public: using char_type = charT; using int_type = traits::int_type; using pos_type = traits::pos_type; using off_type = traits::off_type; using traits_type = traits; using allocator_type = Allocator; using streambuf_type = basic_streambuf<charT, traits>; using syncbuf_type = basic_syncbuf<charT, traits, Allocator>; / [syncstream.osyncstream.cons], construction and destruction basic_osyncstream(streambuf_type*, const Allocator&); explicit basic_osyncstream(streambuf_type* obuf) : basic_osyncstream(obuf, Allocator() {} basic_osyncstream(basic_ostream<charT, traits>& os, const Allocator& allocator) : basic_osyncstream(os.rdbuf(), allocator) {} explicit basic_osyncstream(basic_ostream<charT, traits>& os) : basic_osyncstream(os, Allocator() {} basic_osyncstream(basic_osyncstream&&) noexcept; ~basic_osyncstream(); / assignment basic_osyncstream& operator=(basic_osyncstream&&); / [syncstream.osyncstream.members], member functions void emit(); streambuf_type* get_wrapped() const noexcept; syncbuf_type* rdbuf() const noexcept { return const_cast<syncbuf_type*>(addressof(sb)); } private: syncbuf_type sb; / exposition only }; }
1
#
Allocator shall meet the Cpp17Allocator requirements ([allocator.requirements.general]).
2
#
[Example 1: 
A named variable can be used within a block statement for streaming.
{ osyncstream bout(cout); bout << "Hello, "; bout << "World!"; bout << endl; / flush is noted bout << "and more!\n"; } / characters are transferred and cout is flushed — end example]
3
#
[Example 2: 
A temporary object can be used for streaming within a single statement.
osyncstream(cout) << "Hello, " << "World!" << '\n';
In this example, cout is not flushed.
— end example]

31.11.3.2 Construction and destruction [syncstream.osyncstream.cons]

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basic_osyncstream(streambuf_type* buf, const Allocator& allocator);
1
#
[Note 1: 
The member functions of the provided stream buffer can be called from emit() while a lock is held, which might result in a deadlock if used incautiously.
— end note]
3
#
Postconditions: get_wrapped() == buf is true.
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basic_osyncstream(basic_osyncstream&& other) noexcept;
4
#
Effects: Move constructs the base class and sb from the corresponding subobjects of other, and calls basic_ostream<charT, traits>​::​set_rdbuf(addressof(sb).
5
#
Postconditions: The value returned by get_wrapped() is the value returned by other.get_wrapped() prior to calling this constructor.
nullptr == other.get_wrapped() is true.
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void emit();
1
#
Effects: Behaves as an unformatted output function ([ostream.unformatted]).
After constructing a sentry object, calls sb.emit().
If that call returns false, calls setstate(ios_base​::​badbit).
2
#
[Example 1: 
A flush on a basic_osyncstream does not flush immediately: { osyncstream bout(cout); bout << "Hello," << '\n'; / no flush bout.emit(); / characters transferred; cout not flushed bout << "World!" << endl; / flush noted; cout not flushed bout.emit(); / characters transferred; cout flushed bout << "Greetings." << '\n'; / no flush } / characters transferred; cout not flushed
— end example]
3
#
[Example 2: 
The function emit() can be used to handle exceptions from operations on the underlying stream.
{ osyncstream bout(cout); bout << "Hello, " << "World!" << '\n'; try { bout.emit(); } catch (.) { / handle exception } } — end example]
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streambuf_type* get_wrapped() const noexcept;
4
#
[Example 3: 
Obtaining the wrapped stream buffer with get_wrapped() allows wrapping it again with an osyncstream.
For example, { osyncstream bout1(cout); bout1 << "Hello, "; { osyncstream(bout1.get_wrapped() << "Goodbye, " << "Planet!" << '\n'; } bout1 << "World!" << '\n'; } produces the uninterleaved output 
Goodbye, Planet!
Hello, World!
— end example]

31.12 File systems [filesystems]

1
#
Subclause [filesystems] describes operations on file systems and their components, such as paths, regular files, and directories.
2
#
A file system is a collection of files and their attributes.
3
#
A file is an object within a file system that holds user or system data.
Files can be written to, or read from, or both.
A file has certain attributes, including type.
File types include regular files and directories.
Other types of files, such as symbolic links, may be supported by the implementation.
4
#
A directory is a file within a file system that acts as a container of directory entries that contain information about other files, possibly including other directory files.
The parent directory of a directory is the directory that both contains a directory entry for the given directory and is represented by the dot-dot filename ([fs.path.generic]) in the given directory.
The parent directory of other types of files is a directory containing a directory entry for the file under discussion.
5
#
A link is an object that associates a filename with a file.
Several links can associate names with the same file.
A hard link is a link to an existing file.
Some file systems support multiple hard links to a file.
If the last hard link to a file is removed, the file itself is removed.
[Note 1: 
A hard link can be thought of as a shared-ownership smart pointer to a file.
— end note]
A symbolic link is a type of file with the property that when the file is encountered during pathname resolution ([fs.class.path]), a string stored by the file is used to modify the pathname resolution.
[Note 2: 
Symbolic links are often called symlinks.
A symbolic link can be thought of as a raw pointer to a file.
If the file pointed to does not exist, the symbolic link is said to be a “dangling” symbolic link.
— end note]
1
#
Conformance is specified in terms of behavior.
Ideal behavior is not always implementable, so the conformance subclauses take that into account.

31.12.2.2 POSIX conformance [fs.conform.9945]

1
#
Some behavior is specified by reference to POSIX.
How such behavior is actually implemented is unspecified.
[Note 1: 
This constitutes an “as if” rule allowing implementations to call native operating system or other APIs.
— end note]
2
#
Implementations should provide such behavior as it is defined by POSIX.
Implementations shall document any behavior that differs from the behavior defined by POSIX.
Implementations that do not support exact POSIX behavior should provide behavior as close to POSIX behavior as is reasonable given the limitations of actual operating systems and file systems.
If an implementation cannot provide any reasonable behavior, the implementation shall report an error as specified in [fs.err.report].
[Note 2: 
This allows users to rely on an exception being thrown or an error code being set when an implementation cannot provide any reasonable behavior.
— end note]
3
#
Implementations are not required to provide behavior that is not supported by a particular file system.
[Example 1: 
The FAT file system used by some memory cards, camera memory, and floppy disks does not support hard links, symlinks, and many other features of more capable file systems, so implementations are not required to support those features on the FAT file system but instead are required to report an error as described above.
— end example]

31.12.2.3 Operating system dependent behavior conformance [fs.conform.os]

1
#
Behavior that is specified as being operating system dependent is dependent upon the behavior and characteristics of an operating system.
The operating system an implementation is dependent upon is implementation-defined.
2
#
It is permissible for an implementation to be dependent upon an operating system emulator rather than the actual underlying operating system.

31.12.2.4 File system race behavior [fs.race.behavior]

1
#
A file system race is the condition that occurs when multiple threads, processes, or computers interleave access and modification of the same object within a file system.
Behavior is undefined if calls to functions provided by subclause [filesystems] introduce a file system race.
2
#
If the possibility of a file system race would make it unreliable for a program to test for a precondition before calling a function described herein, Preconditions: is not specified for the function.
[Note 1: 
As a design practice, preconditions are not specified when it is unreasonable for a program to detect them prior to calling the function.
— end note]

31.12.3 Requirements [fs.req]

1
#
Throughout subclause [filesystems], char, wchar_t, char8_t, char16_t, and char32_t are collectively called encoded character types.
2
#
Functions with template parameters named EcharT shall not participate in overload resolution unless EcharT is one of the encoded character types.
3
#
Template parameters named InputIterator shall meet the Cpp17InputIterator requirements ([input.iterators]) and shall have a value type that is one of the encoded character types.
4
#
[Note 1: 
Use of an encoded character type implies an associated character set and encoding.
Since signed char and unsigned char have no implied character set and encoding, they are not included as permitted types.
— end note]
5
#
Template parameters named Allocator shall meet the Cpp17Allocator requirements ([allocator.requirements.general]).

31.12.4 Header <filesystem> synopsis [fs.filesystem.syn]

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#include <compare> / see [compare.syn] namespace std::filesystem { / [fs.class.path], paths class path; / [fs.path.nonmember], path non-member functions void swap(path& lhs, path& rhs) noexcept; size_t hash_value(const path& p) noexcept; / [fs.class.filesystem.error], filesystem errors class filesystem_error; / [fs.class.directory.entry], directory entries class directory_entry; / [fs.class.directory.iterator], directory iterators class directory_iterator; / [fs.dir.itr.nonmembers], range access for directory iterators directory_iterator begin(directory_iterator iter) noexcept; directory_iterator end(directory_iterator) noexcept; / [fs.class.rec.dir.itr], recursive directory iterators class recursive_directory_iterator; / [fs.rec.dir.itr.nonmembers], range access for recursive directory iterators recursive_directory_iterator begin(recursive_directory_iterator iter) noexcept; recursive_directory_iterator end(recursive_directory_iterator) noexcept; / [fs.class.file.status], file status class file_status; struct space_info { uintmax_t capacity; uintmax_t free; uintmax_t available; friend bool operator=(const space_info&, const space_info&) = default; }; / [fs.enum], enumerations enum class file_type; enum class perms; enum class perm_options; enum class copy_options; enum class directory_options; using file_time_type = chrono::time_point<chrono::file_clock>; / [fs.op.funcs], filesystem operations path absolute(const path& p); path absolute(const path& p, error_code& ec); path canonical(const path& p); path canonical(const path& p, error_code& ec); void copy(const path& from, const path& to); void copy(const path& from, const path& to, error_code& ec); void copy(const path& from, const path& to, copy_options options); void copy(const path& from, const path& to, copy_options options, error_code& ec); bool copy_file(const path& from, const path& to); bool copy_file(const path& from, const path& to, error_code& ec); bool copy_file(const path& from, const path& to, copy_options option); bool copy_file(const path& from, const path& to, copy_options option, error_code& ec); void copy_symlink(const path& existing_symlink, const path& new_symlink); void copy_symlink(const path& existing_symlink, const path& new_symlink, error_code& ec) noexcept; bool create_directories(const path& p); bool create_directories(const path& p, error_code& ec); bool create_directory(const path& p); bool create_directory(const path& p, error_code& ec) noexcept; bool create_directory(const path& p, const path& attributes); bool create_directory(const path& p, const path& attributes, error_code& ec) noexcept; void create_directory_symlink(const path& to, const path& new_symlink); void create_directory_symlink(const path& to, const path& new_symlink, error_code& ec) noexcept; void create_hard_link(const path& to, const path& new_hard_link); void create_hard_link(const path& to, const path& new_hard_link, error_code& ec) noexcept; void create_symlink(const path& to, const path& new_symlink); void create_symlink(const path& to, const path& new_symlink, error_code& ec) noexcept; path current_path(); path current_path(error_code& ec); void current_path(const path& p); void current_path(const path& p, error_code& ec) noexcept; bool equivalent(const path& p1, const path& p2); bool equivalent(const path& p1, const path& p2, error_code& ec) noexcept; bool exists(file_status s) noexcept; bool exists(const path& p); bool exists(const path& p, error_code& ec) noexcept; uintmax_t file_size(const path& p); uintmax_t file_size(const path& p, error_code& ec) noexcept; uintmax_t hard_link_count(const path& p); uintmax_t hard_link_count(const path& p, error_code& ec) noexcept; bool is_block_file(file_status s) noexcept; bool is_block_file(const path& p); bool is_block_file(const path& p, error_code& ec) noexcept; bool is_character_file(file_status s) noexcept; bool is_character_file(const path& p); bool is_character_file(const path& p, error_code& ec) noexcept; bool is_directory(file_status s) noexcept; bool is_directory(const path& p); bool is_directory(const path& p, error_code& ec) noexcept; bool is_empty(const path& p); bool is_empty(const path& p, error_code& ec); bool is_fifo(file_status s) noexcept; bool is_fifo(const path& p); bool is_fifo(const path& p, error_code& ec) noexcept; bool is_other(file_status s) noexcept; bool is_other(const path& p); bool is_other(const path& p, error_code& ec) noexcept; bool is_regular_file(file_status s) noexcept; bool is_regular_file(const path& p); bool is_regular_file(const path& p, error_code& ec) noexcept; bool is_socket(file_status s) noexcept; bool is_socket(const path& p); bool is_socket(const path& p, error_code& ec) noexcept; bool is_symlink(file_status s) noexcept; bool is_symlink(const path& p); bool is_symlink(const path& p, error_code& ec) noexcept; file_time_type last_write_time(const path& p); file_time_type last_write_time(const path& p, error_code& ec) noexcept; void last_write_time(const path& p, file_time_type new_time); void last_write_time(const path& p, file_time_type new_time, error_code& ec) noexcept; void permissions(const path& p, perms prms, perm_options opts=perm_options::replace); void permissions(const path& p, perms prms, error_code& ec) noexcept; void permissions(const path& p, perms prms, perm_options opts, error_code& ec); path proximate(const path& p, error_code& ec); path proximate(const path& p, const path& base = current_path(); path proximate(const path& p, const path& base, error_code& ec); path read_symlink(const path& p); path read_symlink(const path& p, error_code& ec); path relative(const path& p, error_code& ec); path relative(const path& p, const path& base = current_path(); path relative(const path& p, const path& base, error_code& ec); bool remove(const path& p); bool remove(const path& p, error_code& ec) noexcept; uintmax_t remove_all(const path& p); uintmax_t remove_all(const path& p, error_code& ec); void rename(const path& from, const path& to); void rename(const path& from, const path& to, error_code& ec) noexcept; void resize_file(const path& p, uintmax_t size); void resize_file(const path& p, uintmax_t size, error_code& ec) noexcept; space_info space(const path& p); space_info space(const path& p, error_code& ec) noexcept; file_status status(const path& p); file_status status(const path& p, error_code& ec) noexcept; bool status_known(file_status s) noexcept; file_status symlink_status(const path& p); file_status symlink_status(const path& p, error_code& ec) noexcept; path temp_directory_path(); path temp_directory_path(error_code& ec); path weakly_canonical(const path& p); path weakly_canonical(const path& p, error_code& ec); } namespace std { / [fs.path.fmtr], formatting support template<class charT> struct formatter<filesystem::path, charT>; / [fs.path.hash], hash support template<class T> struct hash; template<> struct hash<filesystem::path>; } namespace std::ranges { template<> inline constexpr bool enable_borrowed_range<filesystem::directory_iterator> = true; template<> inline constexpr bool enable_borrowed_range<filesystem::recursive_directory_iterator> = true; template<> inline constexpr bool enable_view<filesystem::directory_iterator> = true; template<> inline constexpr bool enable_view<filesystem::recursive_directory_iterator> = true; }
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Implementations should ensure that the resolution and range of file_time_type reflect the operating system dependent resolution and range of file time values.

31.12.5 Error reporting [fs.err.report]

1
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Filesystem library functions often provide two overloads, one that throws an exception to report file system errors, and another that sets an error_code.
[Note 1: 
This supports two common use cases:
  • (1.1)
    Uses where file system errors are truly exceptional and indicate a serious failure.
    Throwing an exception is an appropriate response.
  • (1.2)
    Uses where file system errors are routine and do not necessarily represent failure.
    Returning an error code is the most appropriate response.
    This allows application specific error handling, including simply ignoring the error.
— end note]
2
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Functions not having an argument of type error_code& handle errors as follows, unless otherwise specified:
  • (2.1)
    When a call by the implementation to an operating system or other underlying API results in an error that prevents the function from meeting its specifications, an exception of type filesystem_error shall be thrown.
    For functions with a single path argument, that argument shall be passed to the filesystem_error constructor with a single path argument.
    For functions with two path arguments, the first of these arguments shall be passed to the filesystem_error constructor as the path1 argument, and the second shall be passed as the path2 argument.
    The filesystem_error constructor's error_code argument is set as appropriate for the specific operating system dependent error.
  • (2.2)
    Failure to allocate storage is reported by throwing an exception as described in [res.on.exception.handling].
  • (2.3)
    Destructors throw nothing.
3
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Functions having an argument of type error_code& handle errors as follows, unless otherwise specified:
  • (3.1)
    If a call by the implementation to an operating system or other underlying API results in an error that prevents the function from meeting its specifications, the error_code& argument is set as appropriate for the specific operating system dependent error.
    Otherwise, clear() is called on the error_code& argument.
1
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An object of class path represents a path and contains a pathname.
Such an object is concerned only with the lexical and syntactic aspects of a path.
The path does not necessarily exist in external storage, and the pathname is not necessarily valid for the current operating system or for a particular file system.
2
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[Note 1: 
Class path is used to support the differences between the string types used by different operating systems to represent pathnames, and to perform conversions between encodings when necessary.
— end note]
3
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A path is a sequence of elements that identify the location of a file within a filesystem.
The elements are the root-name
The maximum number of elements in the sequence is operating system dependent ([fs.conform.os]).
4
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An absolute path is a path that unambiguously identifies the location of a file without reference to an additional starting location.
The elements of a path that determine if it is absolute are operating system dependent.
A relative path is a path that is not absolute, and as such, only unambiguously identifies the location of a file when resolved relative to an implied starting location.
The elements of a path that determine if it is relative are operating system dependent.
[Note 2: 
Pathnames “.” and “..” are relative paths.
— end note]
5
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A pathname is a character string that represents the name of a path.
Pathnames are formatted according to the generic pathname format grammar ([fs.path.generic]) or according to an operating system dependent native pathname format accepted by the host operating system.
6
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Pathname resolution is the operating system dependent mechanism for resolving a pathname to a particular file in a file hierarchy.
There may be multiple pathnames that resolve to the same file.
[Example 1: 
For POSIX-based operating systems, this mechanism is specified in POSIX, section 4.12, Pathname resolution.
— end example]
namespace std::filesystem { class path { public: using value_type = see below; using string_type = basic_string<value_type>; static constexpr value_type preferred_separator = see below; / [fs.enum.path.format], enumeration format enum format; / [fs.path.construct], constructors and destructor path() noexcept; path(const path& p); path(path&& p) noexcept; path(string_type&& source, format fmt = auto_format); template<class Source> path(const Source& source, format fmt = auto_format); template<class InputIterator> path(InputIterator first, InputIterator last, format fmt = auto_format); template<class Source> path(const Source& source, const locale& loc, format fmt = auto_format); template<class InputIterator> path(InputIterator first, InputIterator last, const locale& loc, format fmt = auto_format); ~path(); / [fs.path.assign], assignments path& operator=(const path& p); path& operator=(path&& p) noexcept; path& operator=(string_type&& source); path& assign(string_type&& source); template<class Source> path& operator=(const Source& source); template<class Source> path& assign(const Source& source); template<class InputIterator> path& assign(InputIterator first, InputIterator last); / [fs.path.append], appends path& operator/=(const path& p); template<class Source> path& operator/=(const Source& source); template<class Source> path& append(const Source& source); template<class InputIterator> path& append(InputIterator first, InputIterator last); / [fs.path.concat], concatenation path& operator+=(const path& x); path& operator+=(const string_type& x); path& operator+=(basic_string_view<value_type> x); path& operator+=(const value_type* x); path& operator+=(value_type x); template<class Source> path& operator+=(const Source& x); template<class EcharT> path& operator+=(EcharT x); template<class Source> path& concat(const Source& x); template<class InputIterator> path& concat(InputIterator first, InputIterator last); / [fs.path.modifiers], modifiers void clear() noexcept; path& make_preferred(); path& remove_filename(); path& replace_filename(const path& replacement); path& replace_extension(const path& replacement = path(); void swap(path& rhs) noexcept; / [fs.path.nonmember], non-member operators friend bool operator=(const path& lhs, const path& rhs) noexcept; friend strong_ordering operator<=>(const path& lhs, const path& rhs) noexcept; friend path operator/(const path& lhs, const path& rhs); / [fs.path.native.obs], native format observers const string_type& native() const noexcept; const value_type* c_str() const noexcept; operator string_type() const; template<class EcharT, class traits = char_traits<EcharT>, class Allocator = allocator<EcharT>> basic_string<EcharT, traits, Allocator> string(const Allocator& a = Allocator() const; std::string display_string() const; std::string system_encoded_string() const; std::wstring wstring() const; std::u8string u8string() const; std::u16string u16string() const; std::u32string u32string() const; / [fs.path.generic.obs], generic format observers template<class EcharT, class traits = char_traits<EcharT>, class Allocator = allocator<EcharT>> basic_string<EcharT, traits, Allocator> generic_string(const Allocator& a = Allocator() const; std::string generic_display_string() const; std::string generic_system_encoded_string() const; std::wstring generic_wstring() const; std::u8string generic_u8string() const; std::u16string generic_u16string() const; std::u32string generic_u32string() const; / [fs.path.compare], compare int compare(const path& p) const noexcept; int compare(const string_type& s) const; int compare(basic_string_view<value_type> s) const; int compare(const value_type* s) const; / [fs.path.decompose], decomposition path root_name() const; path root_directory() const; path root_path() const; path relative_path() const; path parent_path() const; path filename() const; path stem() const; path extension() const; / [fs.path.query], query bool empty() const noexcept; bool has_root_name() const; bool has_root_directory() const; bool has_root_path() const; bool has_relative_path() const; bool has_parent_path() const; bool has_filename() const; bool has_stem() const; bool has_extension() const; bool is_absolute() const; bool is_relative() const; / [fs.path.gen], generation path lexically_normal() const; path lexically_relative(const path& base) const; path lexically_proximate(const path& base) const; / [fs.path.itr], iterators class iterator; using const_iterator = iterator; iterator begin() const; iterator end() const; / [fs.path.io], path inserter and extractor template<class charT, class traits> friend basic_ostream<charT, traits>& operator<(basic_ostream<charT, traits>& os, const path& p); template<class charT, class traits> friend basic_istream<charT, traits>& operator>(basic_istream<charT, traits>& is, path& p); }; }
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value_type is a typedef for the operating system dependent encoded character type used to represent pathnames.
8
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The value of the preferred_separator member is the operating system dependent preferred-separator character ([fs.path.generic]).
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[Example 2: 
For POSIX-based operating systems, value_type is char and preferred_separator is the slash character ('/').
For Windows-based operating systems, value_type is wchar_t and preferred_separator is the backslash character (L'\\').
— end example]

31.12.6.2 Generic pathname format [fs.path.generic]

root-name:
operating system dependent sequences of characters
implementation-defined sequences of characters
filename:
non-empty sequence of characters other than directory-separator characters
preferred-separator:
operating system dependent directory separator character
1
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A filename is the name of a file.
The dot and dot-dot filenames, consisting solely of one and two period characters respectively, have special meaning.
The following characteristics of filenames are operating system dependent:
  • (1.1)
    The permitted characters.
    [Example 1: 
    Some operating systems prohibit the ASCII control characters (0x00 – 0x1F) in filenames.
    — end example]
    [Note 1: 
    Wider portability can be achieved by limiting filename characters to the POSIX Portable Filename Character Set:
    A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
    a b c d e f g h i j k l m n o p q r s t u v w x y z
    0 1 2 3 4 5 6 7 8 9 . _ -
    — end note]
  • (1.2)
    The maximum permitted length.
  • (1.3)
    Filenames that are not permitted.
  • (1.4)
    Filenames that have special meaning.
  • (1.5)
    Case awareness and sensitivity during path resolution.
  • (1.6)
    Special rules that may apply to file types other than regular files, such as directories.
2
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Except in a root-name, multiple successive directory-separator characters are considered to be the same as one directory-separator character.
3
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The dot filename is treated as a reference to the current directory.
The dot-dot filename is treated as a reference to the parent directory.
What the dot-dot filename refers to relative to root-directory is implementation-defined.
Specific filenames may have special meanings for a particular operating system.
4
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A root-name identifies the starting location for pathname resolution ([fs.class.path]).
If there are no operating system dependent root-names, at least one implementation-defined root-name is required.
[Note 2: 
Many operating systems define a name beginning with two directory-separator characters as a root-name that identifies network or other resource locations.
Some operating systems define a single letter followed by a colon as a drive specifier — a root-name identifying a specific device such as a disk drive.
— end note]
5
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If a root-name is otherwise ambiguous, the possibility with the longest sequence of characters is chosen.
[Note 3: 
On a POSIX-like operating system, it is impossible to have a root-name and a relative-path without an intervening root-directory element.
— end note]
6
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Normalization of a generic format pathname means:
1.
If the path is empty, stop.
2.
Replace each slash character in the root-name with a preferred-separator.
3.
[Note 4: 
The generic pathname grammar defines directory-separator as one or more slashes and preferred-separators.
— end note]
4.
Remove each dot filename and any immediately following directory-separator.
5.
As long as any appear, remove a non-dot-dot filename immediately followed by a directory-separator and a dot-dot filename, along with any immediately following directory-separator.
6.
If there is a root-directory, remove all dot-dot filenames and any directory-separators immediately following them.
[Note 5: 
These dot-dot filenames attempt to refer to nonexistent parent directories.
— end note]
7.
If the last filename is dot-dot, remove any trailing directory-separator.
8.
If the path is empty, add a dot.
The result of normalization is a path in normal form, which is said to be normalized.

31.12.6.3.1 Argument format conversions [fs.path.fmt.cvt]

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[Note 1: 
The format conversions described in this subclause are not applied on POSIX-based operating systems because on these systems:
  • (1.1)
    The generic format is acceptable as a native path.
  • (1.2)
    There is no need to distinguish between native format and generic format in function arguments.
  • (1.3)
    Paths for regular files and paths for directories share the same syntax.
— end note]
2
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Several functions are defined to accept detected-format arguments, which are character sequences.
A detected-format argument represents a path using either a pathname in the generic format ([fs.path.generic]) or a pathname in the native format ([fs.class.path]).
Such an argument is taken to be in the generic format if and only if it matches the generic format and is not acceptable to the operating system as a native path.
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[Note 2: 
Some operating systems have no unambiguous way to distinguish between native format and generic format arguments.
This is by design as it simplifies use for operating systems that do not require disambiguation.
It is possible that an implementation for an operating system where disambiguation is needed distinguishes between the formats.
— end note]
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Pathnames are converted as needed between the generic and native formats in an operating-system-dependent manner.
Let G(n) and N(g) in a mathematical sense be the implementation's functions that convert native-to-generic and generic-to-native formats respectively.
If g=G(n) for some n, then G(N(g))=g; if n=N(g) for some g, then N(G(n))=n.
[Note 3: 
Neither G nor N need be invertible.
— end note]
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If the native format requires paths for regular files to be formatted differently from paths for directories, the path shall be treated as a directory path if its last element is a directory-separator, otherwise it shall be treated as a path to a regular file.
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[Note 4: 
A path stores a native format pathname ([fs.path.native.obs]) and acts as if it also stores a generic format pathname, related as given below.
The implementation can generate the generic format pathname based on the native format pathname (and possibly other information) when requested.
— end note]
7
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When a path is constructed from or is assigned a single representation separate from any path, the other representation is selected by the appropriate conversion function (G or N).
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When the (new) value p of one representation of a path is derived from the representation of that or another path, a value q is chosen for the other representation.
The value q converts to p (by G or N as appropriate) if any such value does so; q is otherwise unspecified.
[Note 5: 
If q is the result of converting any path at all, it is the result of converting p.
— end note]

31.12.6.3.2 Type and encoding conversions [fs.path.type.cvt]

1
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The native encoding of an ordinary character string is the operating system dependent current encoding for pathnames ([fs.class.path]).
The native encoding for wide character strings is the implementation-defined execution wide-character set encoding ([character.seq]).
2
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For member function arguments that take character sequences representing paths and for member functions returning strings, value type and encoding conversion is performed if the value type of the argument or return value differs from path​::​value_type.
For the argument or return value, the method of conversion and the encoding to be converted to is determined by its value type:
  • (2.1)
    char: The encoding is the native ordinary encoding.
    The method of conversion, if any, is operating system dependent.
    [Note 1: 
    For POSIX-based operating systems path​::​value_type is char so no conversion from char value type arguments or to char value type return values is performed.
    For Windows-based operating systems, the native ordinary encoding is determined by calling a Windows API function.
    — end note]
    [Note 2: 
    This results in behavior identical to other C and C++ standard library functions that perform file operations using ordinary character strings to identify paths.
    Changing this behavior would be surprising and error-prone.
    — end note]
  • (2.2)
    wchar_t: The encoding is the native wide encoding.
    The method of conversion is unspecified.
    [Note 3: 
    For Windows-based operating systems path​::​value_type is wchar_t so no conversion from wchar_t value type arguments or to wchar_t value type return values is performed.
    — end note]
  • (2.3)
    char8_t: The encoding is UTF-8.
    The method of conversion is unspecified.
  • (2.4)
    char16_t: The encoding is UTF-16.
    The method of conversion is unspecified.
  • (2.5)
    char32_t: The encoding is UTF-32.
    The method of conversion is unspecified.
3
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If the encoding being converted to has no representation for source characters, the resulting converted characters, if any, are unspecified.
Implementations should not modify member function arguments if already of type path​::​value_type.
1
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In addition to the requirements ([fs.req]), function template parameters named Source shall be one of:
  • (1.1)
    basic_string<EcharT, traits, Allocator>.
    A function argument const Source& source shall have an effective range [source.begin(), source.end()).
  • (1.2)
    basic_string_view<EcharT, traits>.
    A function argument const Source& source shall have an effective range [source.begin(), source.end()).
  • (1.3)
    A type meeting the Cpp17InputIterator requirements that iterates over an NTCTS.
    The value type shall be an encoded character type.
    A function argument const Source& source shall have an effective range [source, end) where end is the first iterator value with an element value equal to iterator_traits<Source>​::​value_type().
  • (1.4)
    A character array that after array-to-pointer decay results in a pointer to the start of an NTCTS.
    The value type shall be an encoded character type.
    A function argument const Source& source shall have an effective range [source, end) where end is the first iterator value with an element value equal to iterator_traits<decay_t<Source>>​::​value_type().
2
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Functions taking template parameters named Source shall not participate in overload resolution unless Source denotes a type other than path, and either
  • (2.1)
    Source is a specialization of basic_string or basic_string_view, or
  • (2.2)
    the qualified-id iterator_traits<decay_t<Source>>​::​value_type is valid and denotes a possibly const encoded character type ([temp.deduct]).
3
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[Note 1: 
See path conversions for how the value types above and their encodings convert to path​::​value_type and its encoding.
— end note]
4
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Arguments of type Source shall not be null pointers.
🔗
path() noexcept;
1
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Postconditions: empty() is true.
🔗
path(const path& p); path(path&& p) noexcept;
2
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Effects: Constructs an object of class path having the same pathname in the native and generic formats, respectively, as the original value of p.
In the second form, p is left in a valid but unspecified state.
🔗
path(string_type&& source, format fmt = auto_format);
3
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Effects: Constructs an object of class path for which the pathname in the detected-format of source has the original value of source ([fs.path.fmt.cvt]), converting format if required ([fs.path.fmt.cvt]).
source is left in a valid but unspecified state.
🔗
template<class Source> path(const Source& source, format fmt = auto_format); template<class InputIterator> path(InputIterator first, InputIterator last, format fmt = auto_format);
4
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Effects: Let s be the effective range of source ([fs.path.req]) or the range [first, last), with the encoding converted if required ([fs.path.cvt]).
Finds the detected-format of s ([fs.path.fmt.cvt]) and constructs an object of class path for which the pathname in that format is s.
🔗
template<class Source> path(const Source& source, const locale& loc, format fmt = auto_format); template<class InputIterator> path(InputIterator first, InputIterator last, const locale& loc, format fmt = auto_format);
5
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Mandates: The value type of Source and InputIterator is char.
6
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Effects: Let s be the effective range of source or the range [first, last), after converting the encoding as follows:
  • (6.1)
    If value_type is wchar_t, converts to the native wide encoding ([fs.path.type.cvt]) using the codecvt<​wchar_t, char, mbstate_t> facet of loc.
  • (6.2)
    Otherwise a conversion is performed using the codecvt<wchar_t, char, mbstate_t> facet of loc, and then a second conversion to the current ordinary encoding.
7
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Finds the detected-format of s ([fs.path.fmt.cvt]) and constructs an object of class path for which the pathname in that format is s.
[Example 1: 
A string is to be read from a database that is encoded in ISO/IEC 8859-1, and used to create a directory: namespace fs = std::filesystem; std::string latin1_string = read_latin1_data(); codecvt_8859_1<wchar_t> latin1_facet; std::locale latin1_locale(std::locale(), latin1_facet); fs::create_directory(fs::path(latin1_string, latin1_locale));
For POSIX-based operating systems, the path is constructed by first using latin1_facet to convert ISO/IEC 8859-1 encoded latin1_string to a wide character string in the native wide encoding ([fs.path.type.cvt]).
The resulting wide string is then converted to an ordinary character pathname string in the current native ordinary encoding.
If the native wide encoding is UTF-16 or UTF-32, and the current native ordinary encoding is UTF-8, all of the characters in the ISO/IEC 8859-1 character set will be converted to their Unicode representation, but for other native ordinary encodings some characters may have no representation.
For Windows-based operating systems, the path is constructed by using latin1_facet to convert ISO/IEC 8859-1 encoded latin1_string to a UTF-16 encoded wide character pathname string.
All of the characters in the ISO/IEC 8859-1 character set will be converted to their Unicode representation.
— end example]
🔗
path& operator=(const path& p);
1
#
Effects: If *this and p are the same object, has no effect.
Otherwise, sets both respective pathnames of *this to the respective pathnames of p.
2
#
Returns: *this.
🔗
path& operator=(path&& p) noexcept;
3
#
Effects: If *this and p are the same object, has no effect.
Otherwise, sets both respective pathnames of *this to the respective pathnames of p.
p is left in a valid but unspecified state.
[Note 1: 
A valid implementation is swap(p).
— end note]
4
#
Returns: *this.
🔗
path& operator=(string_type&& source); path& assign(string_type&& source);
5
#
Effects: Sets the pathname in the detected-format of source to the original value of source.
source is left in a valid but unspecified state.
6
#
Returns: *this.
🔗
template<class Source> path& operator=(const Source& source); template<class Source> path& assign(const Source& source); template<class InputIterator> path& assign(InputIterator first, InputIterator last);
7
#
Effects: Let s be the effective range of source ([fs.path.req]) or the range [first, last), with the encoding converted if required ([fs.path.cvt]).
Finds the detected-format of s ([fs.path.fmt.cvt]) and sets the pathname in that format to s.
8
#
The append operations use operator/= to denote their semantic effect of appending preferred-separator when needed.
🔗
path& operator/=(const path& p);
2
#
Effects: If p.is_absolute() || (p.has_root_name() && p.root_name() != root_name(), then operator=(p).
3
#
Otherwise, modifies *this as if by these steps:
  • (3.1)
    If p.has_root_directory(), then removes any root directory and relative path from the generic format pathname.
    Otherwise, if !has_root_directory() && is_absolute() is true or if has_filename() is true, then appends path​::​preferred_separator to the generic format pathname.
  • (3.2)
    Then appends the native format pathname of p, omitting any root-name from its generic format pathname, to the native format pathname.
4
#
[Example 1: 
Even if /host is interpreted as a root-name, both of the paths path("/host")/"foo" and path("/host/")/"foo" equal "/host/foo" (although the former might use backslash as the preferred separator).
Expression examples: / On POSIX, path("foo") /= path(""); / yields path("foo/") path("foo") /= path("/bar"); / yields path("/bar") / On Windows, path("foo") /= path(""); / yields path("foo\\") path("foo") /= path("/bar"); / yields path("/bar") path("foo") /= path("c:/bar"); / yields path("c:/bar") path("foo") /= path("c:"); / yields path("c:") path("c:") /= path(""); / yields path("c:") path("c:foo") /= path("/bar"); / yields path("c:/bar") path("c:foo") /= path("c:bar"); / yields path("c:foo\\bar")
— end example]
5
#
Returns: *this.
🔗
template<class Source> path& operator/=(const Source& source); template<class Source> path& append(const Source& source);
6
#
Effects: Equivalent to: return operator/=(path(source));
🔗
template<class InputIterator> path& append(InputIterator first, InputIterator last);
7
#
Effects: Equivalent to: return operator/=(path(first, last));
🔗
path& operator+=(const path& x); path& operator+=(const string_type& x); path& operator+=(basic_string_view<value_type> x); path& operator+=(const value_type* x); template<class Source> path& operator+=(const Source& x); template<class Source> path& concat(const Source& x);
1
#
Effects: Appends path(x).native() to the pathname in the native format.
[Note 1: 
This directly manipulates the value of native(), which is not necessarily portable between operating systems.
— end note]
2
#
Returns: *this.
🔗
path& operator+=(value_type x); template<class EcharT> path& operator+=(EcharT x);
3
#
Effects: Equivalent to: return *this += basic_string_view(&x, 1);
🔗
template<class InputIterator> path& concat(InputIterator first, InputIterator last);
4
#
Effects: Equivalent to: return *this += path(first, last);
🔗
void clear() noexcept;
1
#
Postconditions: empty() is true.
🔗
path& make_preferred();
2
#
Effects: Each directory-separator of the pathname in the generic format is converted to preferred-separator.
3
#
[Example 1: path p("foo/bar"); std::cout << p << '\n'; p.make_preferred(); std::cout << p << '\n';
On an operating system where preferred-separator is a slash, the output is: "foo/bar" "foo/bar"
On an operating system where preferred-separator is a backslash, the output is: "foo/bar" "foo\bar"
— end example]
🔗
path& remove_filename();
5
#
[Example 2: path("foo/bar").remove_filename(); / yields "foo/" path("foo/").remove_filename(); / yields "foo/" path("/foo").remove_filename(); / yields "/" path("/").remove_filename(); / yields "/" — end example]
🔗
path& replace_filename(const path& replacement);
9
#
Effects: Equivalent to: remove_filename(); operator/=(replacement);
10
#
[Example 3: path("/foo").replace_filename("bar"); / yields "/bar" on POSIX path("/").replace_filename("bar"); / yields "/bar" on POSIX — end example]
🔗
path& replace_extension(const path& replacement = path();
12
#
Effects:
  • (12.1)
    Any existing extension() ([fs.path.decompose]) is removed from the pathname in the generic format, then
  • (12.2)
    If replacement is not empty and does not begin with a dot character, a dot character is appended to the pathname in the generic format, then
  • (12.3)
    operator+=(replacement);.
13
#
Returns: *this.
🔗
void swap(path& rhs) noexcept;
14
#
The string returned by all native format observers is in the native pathname format ([fs.class.path]).
🔗
const string_type& native() const noexcept;
2
#
Returns: The pathname in the native format.
🔗
const value_type* c_str() const noexcept;
3
#
Effects: Equivalent to: return native().c_str();
🔗
operator string_type() const;
4
#
Returns: native().
🔗
template<class EcharT, class traits = char_traits<EcharT>, class Allocator = allocator<EcharT>> basic_string<EcharT, traits, Allocator> string(const Allocator& a = Allocator() const;
5
#
Remarks: All memory allocation, including for the return value, shall be performed by a.
Conversion, if any, is specified by [fs.path.cvt].
🔗
std::string system_encoded_string() const; std::wstring wstring() const; std::u8string u8string() const; std::u16string u16string() const; std::u32string u32string() const;
7
#
Remarks: Conversion, if any, is performed as specified by [fs.path.cvt].
🔗
std::string display_string() const;
9
#
Returns: std​::​format("{}", *this).
[Note 1: 
The returned string is suitable for use with formatting ([format.functions]) and print functions ([print.fun]).
— end note]

31.12.6.5.7 Generic format observers [fs.path.generic.obs]

1
#
Generic format observer functions return strings formatted according to the generic pathname format.
A single slash ('/') character is used as the directory-separator.
2
#
[Example 1: 
On an operating system that uses backslash as its preferred-separator, path("foo\\bar").generic_string() returns "foo/bar".
— end example]
🔗
template<class EcharT, class traits = char_traits<EcharT>, class Allocator = allocator<EcharT>> basic_string<EcharT, traits, Allocator> generic_string(const Allocator& a = Allocator() const;
3
#
Remarks: All memory allocation, including for the return value, shall be performed by a.
Conversion, if any, is specified by [fs.path.cvt].
🔗
std::string generic_system_encoded_string() const; std::wstring generic_wstring() const; std::u8string generic_u8string() const; std::u16string generic_u16string() const; std::u32string generic_u32string() const;
5
#
Remarks: Conversion, if any, is specified by [fs.path.cvt].
🔗
std::string generic_display_string() const;
7
#
Returns: std​::​format("{:g}", *this).
[Note 1: 
The returned string is suitable for use with formatting ([format.functions]) and print functions ([print.fun]).
— end note]
🔗
int compare(const path& p) const noexcept;
1
#
Returns:
  • (1.1)
    Let rootNameComparison be the result of this->root_name().native().compare(p.root_name().native().
    If rootNameComparison is not 0, rootNameComparison.
  • (1.2)
    Otherwise, if !this->has_root_directory() and p.has_root_directory(), a value less than 0.
  • (1.3)
    Otherwise, if this->has_root_directory() and !p.has_root_directory(), a value greater than 0.
  • (1.4)
    Otherwise, if native() for the elements of this->relative_path() are lexicographically less than native() for the elements of p.relative_path(), a value less than 0.
  • (1.5)
    Otherwise, if native() for the elements of this->relative_path() are lexicographically greater than native() for the elements of p.relative_path(), a value greater than 0.
  • (1.6)
    Otherwise, 0.
🔗
int compare(const string_type& s) const; int compare(basic_string_view<value_type> s) const; int compare(const value_type* s) const;
2
#
Effects: Equivalent to: return compare(path(s));
🔗
path root_name() const;
1
#
Returns: root-name, if the pathname in the generic format includes root-name, otherwise path().
🔗
path root_directory() const;
2
#
Returns: root-directory, if the pathname in the generic format includes root-directory, otherwise path().
🔗
path root_path() const;
3
#
Returns: root_name() / root_directory().
🔗
path relative_path() const;
4
#
Returns: A path composed from the pathname in the generic format, if empty() is false, beginning with the first filename after root_path().
Otherwise, path().
🔗
path parent_path() const;
5
#
Returns: *this if has_relative_path() is false, otherwise a path whose generic format pathname is the longest prefix of the generic format pathname of *this that produces one fewer element in its iteration.
🔗
path filename() const;
6
#
[Example 1: path("/foo/bar.txt").filename(); / yields "bar.txt" path("/foo/bar").filename(); / yields "bar" path("/foo/bar/").filename(); / yields "" path("/").filename(); / yields "" path("/host").filename(); / yields "" path(".").filename(); / yields "." path("..").filename(); / yields ".." — end example]
🔗
path stem() const;
8
#
Returns: Let f be the generic format pathname of filename().
Returns a path whose pathname in the generic format is
  • (8.1)
    f, if it contains no periods other than a leading period or consists solely of one or two periods;
  • (8.2)
    otherwise, the prefix of f ending before its last period.
9
#
[Example 2: std::cout << path("/foo/bar.txt").stem(); / outputs "bar" path p = "foo.bar.baz.tar"; for (; !p.extension().empty(); p = p.stem() std::cout << p.extension() << '\n'; / outputs: .tar / .baz / .bar — end example]
🔗
path extension() const;
10
#
Returns: A path whose pathname in the generic format is the suffix of filename() not included in stem().
11
#
[Example 3: path("/foo/bar.txt").extension(); / yields ".txt" and stem() is "bar" path("/foo/bar").extension(); / yields "" and stem() is "bar" path("/foo/.profile").extension(); / yields "" and stem() is ".profile" path(".bar").extension(); / yields "" and stem() is ".bar" path("..bar").extension(); / yields ".bar" and stem() is "." — end example]
12
#
[Note 1: 
The period is included in the return value so that it is possible to distinguish between no extension and an empty extension.
— end note]
13
#
[Note 2: 
On non-POSIX operating systems, for a path p, it is possible that p.stem() + p.extension() == p.filename() is false, even though the generic format pathnames are the same.
— end note]
🔗
bool empty() const noexcept;
1
#
Returns: true if the pathname in the generic format is empty, otherwise false.
🔗
bool has_root_path() const;
2
#
Returns: !root_path().empty().
🔗
bool has_root_name() const;
3
#
Returns: !root_name().empty().
🔗
bool has_root_directory() const;
4
#
Returns: !root_directory().empty().
🔗
bool has_relative_path() const;
5
#
Returns: !relative_path().empty().
🔗
bool has_parent_path() const;
6
#
Returns: !parent_path().empty().
🔗
bool has_filename() const;
7
#
Returns: !filename().empty().
🔗
bool has_stem() const;
8
#
Returns: !stem().empty().
🔗
bool has_extension() const;
9
#
Returns: !extension().empty().
🔗
bool is_absolute() const;
10
#
Returns: true if the pathname in the native format contains an absolute path ([fs.class.path]), otherwise false.
11
#
[Example 1: 
path("/").is_absolute() is true for POSIX-based operating systems, and false for Windows-based operating systems.
— end example]
🔗
bool is_relative() const;
12
#
Returns: !is_absolute().
🔗
path lexically_normal() const;
1
#
Returns: A path whose pathname in the generic format is the normal form ([fs.path.generic]) of the pathname in the generic format of *this.
2
#
[Example 1: assert(path("foo/./bar/..").lexically_normal() == "foo/"); assert(path("foo/./bar/../").lexically_normal() == "foo/");
The above assertions will succeed.
On Windows, the returned path's directory-separator characters will be backslashes rather than slashes, but that does not affect path equality.
— end example]
🔗
path lexically_relative(const path& base) const;
3
#
Effects: If:
  • (3.1)
    root_name() != base.root_name() is true, or
  • (3.2)
    is_absolute() != base.is_absolute() is true, or
  • (3.3)
    !has_root_directory() && base.has_root_directory() is true, or
  • (3.4)
    any filename in relative_path() or base.relative_path() can be interpreted as a root-name,
returns path().
[Note 1: 
On a POSIX implementation, no filename in a relative-path is acceptable as a root-name.
— end note]
Determines the first mismatched element of *this and base as if by: auto [a, b] = mismatch(begin(), end(), base.begin(), base.end();
Then,
  • (3.5)
    if a == end() and b == base.end(), returns path("."); otherwise
  • (3.6)
    let n be the number of filename elements in [b, base.end()) that are not dot or dot-dot or empty, minus the number that are dot-dot.
    If n<0, returns path(); otherwise
  • (3.7)
    if n == 0 and (a == end() || a->empty(), returns path("."); otherwise
  • (3.8)
    returns an object of class path that is default-constructed, followed by
    • (3.8.1)
      application of operator/=(path("..") n times, and then
    • (3.8.2)
      application of operator/= for each element in [a, end()).
4
#
[Example 2: assert(path("/a/d").lexically_relative("/a/b/c") == "../../d"); assert(path("/a/b/c").lexically_relative("/a/d") == "../b/c"); assert(path("a/b/c").lexically_relative("a") == "b/c"); assert(path("a/b/c").lexically_relative("a/b/c/x/y") == "../.."); assert(path("a/b/c").lexically_relative("a/b/c") == "."); assert(path("a/b").lexically_relative("c/d") == "../../a/b");
The above assertions will succeed.
On Windows, the returned path's directory-separator characters will be backslashes rather than slashes, but that does not affect path equality.
— end example]
6
#
[Note 2: 
If symlink following semantics are desired, use the operational function relative().
— end note]
7
#
[Note 3: 
If normalization ([fs.path.generic]) is needed to ensure consistent matching of elements, apply lexically_normal() to *this, base, or both.
— end note]
🔗
path lexically_proximate(const path& base) const;
8
#
Returns: If the value of lexically_relative(base) is not an empty path, return it.
Otherwise return *this.
9
#
[Note 4: 
If symlink following semantics are desired, use the operational function proximate().
— end note]
10
#
[Note 5: 
If normalization ([fs.path.generic]) is needed to ensure consistent matching of elements, apply lexically_normal() to *this, base, or both.
— end note]
1
#
Path iterators iterate over the elements of the pathname in the generic format.
2
#
A path​::​iterator is a constant iterator meeting all the requirements of a bidirectional iterator except that, for dereferenceable iterators a and b of type path​::​iterator with a == b, there is no requirement that *a and *b are bound to the same object.
Its value_type is path.
3
#
Calling any non-const member function of a path object invalidates all iterators referring to elements of that object.
4
#
For the elements of the pathname in the generic format, the forward traversal order is as follows:
5
#
The backward traversal order is the reverse of forward traversal.
🔗
iterator begin() const;
6
#
Returns: An iterator for the first present element in the traversal list above.
If no elements are present, the end iterator.
🔗
iterator end() const;
7
#
Returns: The end iterator.

31.12.6.7 Inserter and extractor [fs.path.io]

🔗
template<class charT, class traits> friend basic_ostream<charT, traits>& operator<(basic_ostream<charT, traits>& os, const path& p);
1
#
Returns: os.
🔗
template<class charT, class traits> friend basic_istream<charT, traits>& operator>(basic_istream<charT, traits>& is, path& p);
3
#
Effects: Equivalent to: basic_string<charT, traits> tmp; is >> quoted(tmp); p = tmp;
4
#
Returns: is.

31.12.6.8 Non-member functions [fs.path.nonmember]

🔗
void swap(path& lhs, path& rhs) noexcept;
1
#
Effects: Equivalent to lhs.swap(rhs).
🔗
size_t hash_value(const path& p) noexcept;
2
#
Returns: A hash value for the path p.
If for two paths, p1 == p2 then hash_value(p1) == hash_value(p2).
🔗
friend bool operator=(const path& lhs, const path& rhs) noexcept;
3
#
[Note 1: 
Path equality and path equivalence have different semantics.
  • (4.1)
    Equality is determined by the path non-member operator=, which considers the two paths' lexical representations only.
    [Example 1: 
    path("foo") == "bar" is never true.
    — end example]
  • (4.2)
    Equivalence is determined by the equivalent() non-member function, which determines if two paths resolve ([fs.class.path]) to the same file system entity.
    [Example 2: 
    equivalent("foo", "bar") will be true when both paths resolve to the same file.
    — end example]
— end note]
🔗
friend strong_ordering operator<=>(const path& lhs, const path& rhs) noexcept;
5
#
Returns: lhs.compare(rhs) <=> 0.
🔗
friend path operator/(const path& lhs, const path& rhs);
6
#
Effects: Equivalent to: return path(lhs) /= rhs;

31.12.6.9 Formatting support [fs.path.fmtr]

31.12.6.9.1 Formatting support overview [fs.path.fmtr.general]

🔗
namespace std { template<class charT> struct formatter<filesystem::path, charT> { constexpr void set_debug_format(); constexpr typename basic_format_parse_context<charT>::iterator parse(basic_format_parse_context<charT>& ctx); template<class FormatContext> typename FormatContext::iterator format(const filesystem::path& path, FormatContext& ctx) const; }; }

31.12.6.9.2 Formatting support functions [fs.path.fmtr.funcs]

1
#
Formatting of paths uses formatting specifiers of the form
path-format-spec:
fill-and-align
where the productions fill-and-align and width are described in [format.string].
If the ? option is used then the path is formatted as an escaped string ([format.string.escaped]).
🔗
constexpr void set_debug_format();
2
#
Effects: Modifies the state of the formatter to be as if the path-format-spec parsed by the last call to parse contained the ? option.
🔗
constexpr typename basic_format_parse_context<charT>::iterator parse(basic_format_parse_context<charT>& ctx);
3
#
Effects: Parses the format specifier as a path-format-spec and stores the parsed specifiers in *this.
4
#
Returns: An iterator past the end of the path-format-spec.
🔗
template<class FormatContext> typename FormatContext::iterator format(const filesystem::path& p, FormatContext& ctx) const;
5
#
Effects: Let s be p.generic_string<filesystem​::​path​::​value_type>() if the g option is used, otherwise p.native().
Writes s into ctx.out(), adjusted according to the path-format-spec.
If charT is char, path​::​value_type is wchar_t, and the literal encoding is UTF-8, then the escaped path is transcoded from the native encoding for wide character strings to UTF-8 with maximal subparts of ill-formed subsequences substituted with U+fffd replacement character per the Unicode Standard, Chapter 3.9 U+fffd Substitution in Conversion.
If charT and path​::​value_type are the same then no transcoding is performed.
Otherwise, transcoding is implementation-defined.
6
#
Returns: An iterator past the end of the output range.
🔗
template<> struct hash<filesystem::path>;
1
#
For an object p of type filesystem​::​path, hash<filesystem​::​path>()(p) evaluates to the same result as filesystem​::​hash_value(p).

31.12.7 Class filesystem_error [fs.class.filesystem.error]

🔗
namespace std::filesystem { class filesystem_error : public system_error { public: filesystem_error(const string& what_arg, error_code ec); filesystem_error(const string& what_arg, const path& p1, error_code ec); filesystem_error(const string& what_arg, const path& p1, const path& p2, error_code ec); const path& path1() const noexcept; const path& path2() const noexcept; const char* what() const noexcept override; }; }
1
#
The class filesystem_error defines the type of objects thrown as exceptions to report file system errors from functions described in subclause [filesystems].
1
#
Constructors are provided that store zero, one, or two paths associated with an error.
🔗
filesystem_error(const string& what_arg, error_code ec);
2
#
Postconditions:
  • (2.1)
    code() == ec is true,
  • (2.2)
    path1().empty() is true,
  • (2.3)
    path2().empty() is true, and
  • (2.4)
    string_view(what().find(what_arg.c_str() != string_view​::​npos is true.
🔗
filesystem_error(const string& what_arg, const path& p1, error_code ec);
3
#
Postconditions:
  • (3.1)
    code() == ec is true,
  • (3.2)
    path1() returns a reference to the stored copy of p1,
  • (3.3)
    path2().empty() is true, and
  • (3.4)
    string_view(what().find(what_arg.c_str() != string_view​::​npos is true.
🔗
filesystem_error(const string& what_arg, const path& p1, const path& p2, error_code ec);
4
#
Postconditions:
  • (4.1)
    code() == ec,
  • (4.2)
    path1() returns a reference to the stored copy of p1,
  • (4.3)
    path2() returns a reference to the stored copy of p2, and
  • (4.4)
    string_view(what().find(what_arg.c_str() != string_view​::​npos.
🔗
const path& path1() const noexcept;
5
#
Returns: A reference to the copy of p1 stored by the constructor, or, if none, an empty path.
🔗
const path& path2() const noexcept;
6
#
Returns: A reference to the copy of p2 stored by the constructor, or, if none, an empty path.
🔗
const char* what() const noexcept override;
7
#
Returns: An ntbs that incorporates the what_arg argument supplied to the constructor.
The exact format is unspecified.
Implementations should include the system_error​::​what() string and the pathnames of path1 and path2 in the native format in the returned string.

31.12.8 Enumerations [fs.enum]

31.12.8.1 Enum path​::​format [fs.enum.path.format]

1
#
This enum specifies constants used to identify the format of the character sequence, with the meanings listed in Table 148.
Table 148 — Enum path​::​format [tab:fs.enum.path.format]
🔗
Name
Meaning
🔗
native_format
The native pathname format.
🔗
generic_format
The generic pathname format.
🔗
auto_format
The interpretation of the format of the character sequence is implementation-defined.
The implementation may inspect the content of the character sequence to determine the format.
Recommended practice: For POSIX-based systems, native and generic formats are equivalent and the character sequence should always be interpreted in the same way.

31.12.8.2 Enum class file_type [fs.enum.file.type]

1
#
This enum class specifies constants used to identify file types, with the meanings listed in Table 149.
The values of the constants are distinct.
Table 149 — Enum class file_type [tab:fs.enum.file.type]
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Constant
Meaning
🔗
The type of the file has not been determined or an error occurred while trying to determine the type.
🔗
Pseudo-type indicating the file was not found.
[Note 1: 
The file not being found is not considered an error while determining the type of a file.
— end note]
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Regular file
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Directory file
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Symbolic link file
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Block special file
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Character special file
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FIFO or pipe file
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Socket file
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implementation-defined
Implementations that support file systems having file types in addition to the above file_type types shall supply implementation-defined file_type constants to separately identify each of those additional file types
🔗
The file exists but the type cannot be determined

31.12.8.3 Enum class copy_options [fs.enum.copy.opts]

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#
The enum class type copy_options is a bitmask type ([bitmask.types]) that specifies bitmask constants used to control the semantics of copy operations.
The constants are specified in option groups with the meanings listed in Table 150.
The constant none represents the empty bitmask, and is shown in each option group for purposes of exposition; implementations shall provide only a single definition.
Every other constant in the table represents a distinct bitmask element.
Table 150 — Enum class copy_options [tab:fs.enum.copy.opts]
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Option group controlling copy_file function effects for existing target files
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Constant
Meaning
🔗
(Default) Error; file already exists.
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Do not overwrite existing file, do not report an error.
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Overwrite the existing file.
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Overwrite the existing file if it is older than the replacement file.
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Option group controlling copy function effects for subdirectories
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Constant
Meaning
🔗
(Default) Do not copy subdirectories.
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Recursively copy subdirectories and their contents.
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Option group controlling copy function effects for symbolic links
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Constant
Meaning
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(Default) Follow symbolic links.
🔗
Copy symbolic links as symbolic links rather than copying the files that they point to.
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Ignore symbolic links.
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Option group controlling copy function effects for choosing the form of copying
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Constant
Meaning
🔗
(Default) Copy content.
🔗
Copy directory structure only, do not copy non-directory files.
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Make symbolic links instead of copies of files.
The source path shall be an absolute path unless the destination path is in the current directory.
🔗
Make hard links instead of copies of files.

31.12.8.4 Enum class perms [fs.enum.perms]

1
#
The enum class type perms is a bitmask type ([bitmask.types]) that specifies bitmask constants used to identify file permissions, with the meanings listed in Table 151.
Table 151 — Enum class perms [tab:fs.enum.perms]
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Name
Value
POSIX
Definition or notes
🔗
(octal)
macro
🔗
0
There are no permissions set for the file.
🔗
0400
S_IRUSR
Read permission, owner
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0200
S_IWUSR
Write permission, owner
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0100
S_IXUSR
Execute/search permission, owner
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0700
S_IRWXU
Read, write, execute/search by owner;
owner_read | owner_write | owner_exec
🔗
040
S_IRGRP
Read permission, group
🔗
020
S_IWGRP
Write permission, group
🔗
010
S_IXGRP
Execute/search permission, group
🔗
070
S_IRWXG
Read, write, execute/search by group;
group_read | group_write | group_exec
🔗
04
S_IROTH
Read permission, others
🔗
02
S_IWOTH
Write permission, others
🔗
01
S_IXOTH
Execute/search permission, others
🔗
07
S_IRWXO
Read, write, execute/search by others;
others_read | others_write | others_exec
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0777
owner_all | group_all | others_all
🔗
04000
S_ISUID
Set-user-ID on execution
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02000
S_ISGID
Set-group-ID on execution
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01000
S_ISVTX
Operating system dependent.
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07777
all | set_uid | set_gid | sticky_bit
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0xFFFF
The permissions are not known, such as when a file_status object is created without specifying the permissions

31.12.8.5 Enum class perm_options [fs.enum.perm.opts]

1
#
The enum class type perm_options is a bitmask type ([bitmask.types]) that specifies bitmask constants used to control the semantics of permissions operations, with the meanings listed in Table 152.
The bitmask constants are bitmask elements.
In Table 152 perm denotes a value of type perms passed to permissions.
Table 152 — Enum class perm_options [tab:fs.enum.perm.opts]
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Name
Meaning
🔗
permissions shall replace the file's permission bits with perm
🔗
permissions shall replace the file's permission bits with the bitwise or of perm and the file's current permission bits.
🔗
permissions shall replace the file's permission bits with the bitwise and of the complement of perm and the file's current permission bits.
🔗
permissions shall change the permissions of a symbolic link itself rather than the permissions of the file the link resolves to.

31.12.8.6 Enum class directory_options [fs.enum.dir.opts]

1
#
The enum class type directory_options is a bitmask type ([bitmask.types]) that specifies bitmask constants used to identify directory traversal options, with the meanings listed in Table 153.
The constant none represents the empty bitmask; every other constant in the table represents a distinct bitmask element.
Table 153 — Enum class directory_options [tab:fs.enum.dir.opts]
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Name
Meaning
🔗
(Default) Skip directory symlinks, permission denied is an error.
🔗
Follow rather than skip directory symlinks.
🔗
Skip directories that would otherwise result in permission denied.
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namespace std::filesystem { class file_status { public: / [fs.file.status.cons], constructors and destructor file_status() noexcept : file_status(file_type::none) {} explicit file_status(file_type ft, perms prms = perms::unknown) noexcept; file_status(const file_status&) noexcept = default; file_status(file_status&&) noexcept = default; ~file_status(); / assignments file_status& operator=(const file_status&) noexcept = default; file_status& operator=(file_status&&) noexcept = default; / [fs.file.status.mods], modifiers void type(file_type ft) noexcept; void permissions(perms prms) noexcept; / [fs.file.status.obs], observers file_type type() const noexcept; perms permissions() const noexcept; friend bool operator=(const file_status& lhs, const file_status& rhs) noexcept { return lhs.type() == rhs.type() && lhs.permissions() == rhs.permissions(); } }; }
1
#
An object of type file_status stores information about the type and permissions of a file.
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explicit file_status(file_type ft, perms prms = perms::unknown) noexcept;
1
#
Postconditions: type() == ft and permissions() == prms.
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file_type type() const noexcept;
1
#
Returns: The value of type() specified by the postconditions of the most recent call to a constructor, operator=, or type(file_type) function.
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perms permissions() const noexcept;
2
#
Returns: The value of permissions() specified by the postconditions of the most recent call to a constructor, operator=, or permissions(perms) function.
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void type(file_type ft) noexcept;
1
#
Postconditions: type() == ft.
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void permissions(perms prms) noexcept;
2
#
Postconditions: permissions() == prms.

31.12.10 Class directory_entry [fs.class.directory.entry]

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namespace std::filesystem { class directory_entry { public: / [fs.dir.entry.cons], constructors and destructor directory_entry() noexcept = default; directory_entry(const directory_entry&) = default; directory_entry(directory_entry&&) noexcept = default; explicit directory_entry(const filesystem::path& p); directory_entry(const filesystem::path& p, error_code& ec); ~directory_entry(); / assignments directory_entry& operator=(const directory_entry&) = default; directory_entry& operator=(directory_entry&&) noexcept = default; / [fs.dir.entry.mods], modifiers void assign(const filesystem::path& p); void assign(const filesystem::path& p, error_code& ec); void replace_filename(const filesystem::path& p); void replace_filename(const filesystem::path& p, error_code& ec); void refresh(); void refresh(error_code& ec) noexcept; / [fs.dir.entry.obs], observers const filesystem::path& path() const noexcept; operator const filesystem::path&() const noexcept; bool exists() const; bool exists(error_code& ec) const noexcept; bool is_block_file() const; bool is_block_file(error_code& ec) const noexcept; bool is_character_file() const; bool is_character_file(error_code& ec) const noexcept; bool is_directory() const; bool is_directory(error_code& ec) const noexcept; bool is_fifo() const; bool is_fifo(error_code& ec) const noexcept; bool is_other() const; bool is_other(error_code& ec) const noexcept; bool is_regular_file() const; bool is_regular_file(error_code& ec) const noexcept; bool is_socket() const; bool is_socket(error_code& ec) const noexcept; bool is_symlink() const; bool is_symlink(error_code& ec) const noexcept; uintmax_t file_size() const; uintmax_t file_size(error_code& ec) const noexcept; uintmax_t hard_link_count() const; uintmax_t hard_link_count(error_code& ec) const noexcept; file_time_type last_write_time() const; file_time_type last_write_time(error_code& ec) const noexcept; file_status status() const; file_status status(error_code& ec) const noexcept; file_status symlink_status() const; file_status symlink_status(error_code& ec) const noexcept; bool operator=(const directory_entry& rhs) const noexcept; strong_ordering operator<=>(const directory_entry& rhs) const noexcept; / [fs.dir.entry.io], inserter template<class charT, class traits> friend basic_ostream<charT, traits>& operator<(basic_ostream<charT, traits>& os, const directory_entry& d); private: filesystem::path path-object; / exposition only }; }
1
#
A directory_entry object stores a path object and may store additional objects for file attributes such as hard link count, status, symlink status, file size, and last write time.
2
#
Implementations should store such additional file attributes during directory iteration if their values are available and storing the values would allow the implementation to eliminate file system accesses by directory_entry observer functions ([fs.op.funcs]).
Such stored file attribute values are said to be cached.
3
#
[Note 1: 
directory_iterator can cache already available attribute values directly into a directory_entry object without the cost of a call to refresh().
— end note]
4
#
[Example 1: using namespace std::filesystem; / use possibly cached last write time to minimize disk accesses for (auto& x : directory_iterator(".") { std::cout << x.path() << " " << x.last_write_time() << std::endl; } / call refresh() to refresh a stale cache for (auto& x : directory_iterator(".") { lengthy_function(x.path(); / cache becomes stale x.refresh(); std::cout << x.path() << " " << x.last_write_time() << std::endl; }
On implementations that do not cache the last write time, both loops will result in a potentially expensive call to the std​::​filesystem​::​last_write_time function.
On implementations that do cache the last write time, the first loop will use the cached value and so will not result in a potentially expensive call to the std​::​filesystem​::​last_write_time function.
The code is portable to any implementation, regardless of whether or not it employs caching.
— end example]
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explicit directory_entry(const filesystem::path& p); directory_entry(const filesystem::path& p, error_code& ec);
1
#
Postconditions: path() == p if no error occurs, otherwise path() == filesystem​::​path().
3
#
Throws: As specified in [fs.err.report].
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void assign(const filesystem::path& p); void assign(const filesystem::path& p, error_code& ec);
1
#
Effects: Equivalent to path-object = p, then refresh() or refresh(ec), respectively.
If an error occurs, the values of any cached attributes are unspecified.
2
#
Throws: As specified in [fs.err.report].
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void replace_filename(const filesystem::path& p); void replace_filename(const filesystem::path& p, error_code& ec);
3
#
Effects: Equivalent to path-object.replace_filename(p), then refresh() or refresh(ec), respectively.
If an error occurs, the values of any cached attributes are unspecified.
4
#
Throws: As specified in [fs.err.report].
🔗
void refresh(); void refresh(error_code& ec) noexcept;
5
#
Effects: Stores the current values of any cached attributes of the file p resolves to.
If an error occurs, an error is reported ([fs.err.report]) and the values of any cached attributes are unspecified.
6
#
[Note 1: 
Implementations of directory_iterator ([fs.class.directory.iterator]) are prohibited from directly or indirectly calling the refresh function as described in [fs.class.directory.iterator.general].
— end note]
1
#
Unqualified function names in the Returns: elements of the directory_entry observers described below refer to members of the std​::​filesystem namespace.
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const filesystem::path& path() const noexcept; operator const filesystem::path&() const noexcept;
2
#
Returns: path-object.
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bool exists() const; bool exists(error_code& ec) const noexcept;
3
#
Throws: As specified in [fs.err.report].
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bool is_block_file() const; bool is_block_file(error_code& ec) const noexcept;
5
#
Throws: As specified in [fs.err.report].
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bool is_character_file() const; bool is_character_file(error_code& ec) const noexcept;
7
#
Throws: As specified in [fs.err.report].
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bool is_directory() const; bool is_directory(error_code& ec) const noexcept;
9
#
Throws: As specified in [fs.err.report].
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bool is_fifo() const; bool is_fifo(error_code& ec) const noexcept;
11
#
Throws: As specified in [fs.err.report].
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bool is_other() const; bool is_other(error_code& ec) const noexcept;
13
#
Throws: As specified in [fs.err.report].
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bool is_regular_file() const; bool is_regular_file(error_code& ec) const noexcept;
15
#
Throws: As specified in [fs.err.report].
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bool is_socket() const; bool is_socket(error_code& ec) const noexcept;
17
#
Throws: As specified in [fs.err.report].