std::basic_stringbuf<CharT,Traits,Allocator>::seekpos

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()
which - defines whether the input sequences, the output sequence, or both are affected. It can be one or a combination of the following constants:
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

#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

See also

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

© cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.
http://en.cppreference.com/w/cpp/io/basic_stringbuf/seekpos