NAME¶

std::basic_stringbuf::seekpos - std::basic_stringbuf::seekpos

Synopsis¶

protected:

virtual pos_type seekpos( pos_type sp,

std::ios_base::openmode which = std::ios_base::in |
std::ios_base::out );

Repositions std::basic_streambuf::gptr and/or std::basic_streambuf::pptr, if
possible, to the position indicated by sp.

Effectively executes seekoff(off_type(sp), std::ios_base::beg, which).

Parameters¶

sp - stream position, such as one obtained by seekoff() or seekpos()
defines whether the input sequences, the output sequence, or both are
affected. It can be one or a combination of the following constants:
which -
Constant Explanation
in affect the input sequence
out affect the output sequence

Return value¶

sp on success or pos_type(off_type(-1)) on failure.

Notes¶

seekpos() is called by std::basic_streambuf::pubseekpos(), which is called by the
single-argument versions of std::basic_istream::seekg() and
std::basic_ostream::seekp().

Example¶

// Run this code

#include <sstream>
#include <iostream>

struct mybuf : std::stringbuf
{
mybuf(const std::string& str) : std::stringbuf(str) {}

pos_type seekpos(pos_type sp, std::ios_base::openmode which)
{
std::cout << "Before seekpos(" << sp << "), size of the get area is "
<< egptr() - eback() << " with "
<< egptr() - gptr() << " read positions available.\n";

pos_type rc = std::stringbuf::seekpos(sp, which);

std::cout << "seekpos() returns " << rc << ".\nAfter the call, "
<< "size of the get area is "
<< egptr() - eback() << " with "
<< egptr() - gptr() << " read positions available.\n";

return rc;
}
};

int main()
{
mybuf buf("12345");
std::iostream stream(&buf);
stream.seekg(2);
}

Output:¶

Before seekpos(2), size of the get area is 5 with 5 read positions available.
seekpos() returns 2.
After the call, size of the get area is 5 with 3 read positions available.

Defect reports

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

DR Applied to Behavior as published Correct behavior
static constant members of std::ios_base
LWG 375 C++98 were corrected
misspecified as members of
std::basic_ios
LWG 564 C++98 if was unclear how to reposition gptr they are repositioned by
and/or pptr seekoff()

See also¶

pubseekpos invokes seekpos()
(public member function of std::basic_streambuf<CharT,Traits>)
seekoff repositions the next pointer in the input sequence, output sequence, or
[virtual] both, using relative addressing
(virtual protected member function)
seekpos repositions the file position, using absolute addressing
[virtual] (virtual protected member function of std::basic_filebuf<CharT,Traits>)

seekpos repositions the next pointer in the input sequence, output sequence, or
[virtual] both using absolute addressing
(virtual protected member function of std::strstreambuf)