std::basic_stringbuf<CharT,Traits,Allocator>::seekpos - cppreference.com (original) (raw)
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).
[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 #include 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] 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 375 | C++98 | static constant members of std::ios_base weremisspecified as members of std::basic_ios | corrected |
| LWG 564 | C++98 | if was unclear how to reposition gptr and/or pptr | they are repositioned by seekoff() |
[edit] See also
| | invokes seekpos() (public member function of std::basic_streambuf<CharT,Traits>) [edit] | | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | | repositions the next pointer in the input sequence, output sequence, or both, using relative addressing (virtual protected member function) [edit] | | | repositions the file position, using absolute addressing (virtual protected member function of std::basic_filebuf<CharT,Traits>) [edit] | | | repositions the next pointer in the input sequence, output sequence, or both using absolute addressing (virtual protected member function of std::strstreambuf) [edit] |