W3cubDocs

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

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

#include <sstream>
#include <iostream>
 
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