std::basic_ostream<CharT,Traits>::seekp

 

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basic_ostream& seekp( pos_type pos );	(1)
basic_ostream& seekp( off_type off, std::ios_base::seekdir dir );	(2)

Sets the output position indicator of the current associated streambuf object.

Behaves as UnformattedOutputFunction (except without actually performing output). After constructing and checking the sentry object,

(since C++11)

1) if fail() != true, sets the output position indicator to absolute (relative to the beginning of the file) value pos by calling rdbuf()->pubseekpos(pos, std::ios_base::out). In case of failure, calls setstate(std::ios_base::failbit).

2) if fail() != true, sets the output position indicator to offset off relative to dir by calling rdbuf()->pubseekoff(off, dir, std::ios_base::out). In case of failure, calls setstate(std::ios_base::failbit).

Parameters

pos	-	absolute position to set the output position indicator to
off	-	relative position (positive or negative) to set the output position indicator to
dir	-	defines base position to apply the relative offset to. It can be one of the following constants: Constant Explanation beg the beginning of a stream end the ending of a stream cur the current position of stream position indicator

Return value

*this

Exceptions

1,2) May throw std::ios_base::failure in case of failure, if exceptions() & failbit != 0.

Example

Run this code

#include <iostream>
#include <sstream>
 
int main()
{
    std::ostringstream os("hello, world");
    os.seekp(7);
    os << 'W';
    os.seekp(0, std::ios_base::end);
    os << '!';
    os.seekp(0);
    os << 'H';
    std::cout << os.str() << '\n';
}

Output:

Hello, World!

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 129	C++98	there was no way to indicate a failure	sets failbit on failure
LWG 136	C++98	seekp could set the input stream	only sets the output stream
LWG 537	C++98	1. the type of pos was pos_type& 2. the type of off was off_type&	1. corrected to pos_type 2. corrected to off_type
LWG 2341	C++98	the resolution of LWG issue 129 for overload (2) was removed	restored

See also

tellp	returns the output position indicator (public member function)
tellg	returns the input position indicator (public member function of std::basic_istream<CharT,Traits>)
seekg	sets the input position indicator (public member function of std::basic_istream<CharT,Traits>)

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