std::basic_streambuf<CharT,Traits>::sungetc

 

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std::basic_streambuf

Public member functions basic_streambuf::~basic_streambuf      Locales basic_streambuf::pubimbue basic_streambuf::getloc Positioning basic_streambuf::pubsetbuf basic_streambuf::pubseekoff basic_streambuf::pubseekpos basic_streambuf::pubsync Get area basic_streambuf::in_avail basic_streambuf::snextc basic_streambuf::sbumpc basic_streambuf::sgetc basic_streambuf::sgetn Put area basic_streambuf::sputc basic_streambuf::sputn Putback basic_streambuf::sputbackc basic_streambuf::sungetc

Protected member functions basic_streambuf::basic_streambuf basic_streambuf::operator= (C++11) basic_streambuf::swap (C++11) Locales basic_streambuf::imbue Positioning basic_streambuf::setbuf basic_streambuf::seekoff basic_streambuf::seekpos basic_streambuf::sync Get area basic_streambuf::showmanyc basic_streambuf::underflow basic_streambuf::uflow basic_streambuf::xsgetn basic_streambuf::ebackbasic_streambuf::gptrbasic_streambuf::egptr basic_streambuf::gbump basic_streambuf::setg Put area basic_streambuf::xsputn basic_streambuf::overflow basic_streambuf::pbasebasic_streambuf::pptrbasic_streambuf::epptr basic_streambuf::pbump basic_streambuf::setp Putback basic_streambuf::pbackfail

 

int_type sungetc();

If a putback position is available in the get area (gptr() > eback()), then decrements the next pointer (gptr()) and returns the character it now points to.

If a putback position is not available, then calls pbackfail() to back up the input sequence if possible.

The I/O stream function basic_istream::unget is implemented in terms of this function.

Parameters

(none)

Return value

If putback position was available, returns the character that the next pointer is now pointing at, converted to int_type with Traits::to_int_type(*gptr(). The next single-character input from this streambuf will return this character.

If putback position was not available, returns what pbackfail() returns, which is Traits::eof() on failure.

Example

Run this code

#include <iostream>
#include <sstream>
 
int main()
{
    std::stringstream s("abcdef"); / gptr() points to 'a'
    char c1 = s.get(); / c = 'a', gptr() now points to 'b' 
    char c2 = s.rdbuf()->sungetc(); / same as s.unget(): gptr() points to 'a' again 
    char c3 = s.get(); / c3 = 'a', gptr() now points to 'b'
    char c4 = s.get(); / c4 = 'b', gptr() now points to 'c'
    std::cout << c1 << c2 << c3 << c4 << '\n';
 
    s.rdbuf()->sungetc();  / back to 'b'
    s.rdbuf()->sungetc();  / back to 'a'
    int eof = s.rdbuf()->sungetc();  / nothing to unget: pbackfail() fails
    if (eof == EOF)
            std::cout << "Nothing to unget after 'a'\n";
}

Output:

aaab
Nothing to unget after 'a'

See also

sputbackc	puts one character back in the input sequence (public member function)
unget	unextracts a character (public member function of std::basic_istream<CharT,Traits>)

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