std::basic_stringbuf<CharT,Traits,Allocator>::seekpos (3) - Linux Manuals

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

NAME

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