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std::basic_stringbuf::seekpos

From cppreference.com
< cpp‎ | io‎ | basic stringbuf
 
 
Input/output library
I/O manipulators
C-style I/O
Buffers
(deprecated in C++98)
Streams
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File I/O
String I/O
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(deprecated in C++98)
(deprecated in C++98)
(deprecated in C++98)
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(C++11)
 
 
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)

Contents

[edit] 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

[edit] Return value

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

[edit] 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()

[edit] 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

[edit] See also

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