std::basic_stringbuf<CharT,Traits,Allocator>::seekpos
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basic_stringbuf::seekpos
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protected:
virtual pos_type seekpos( pos_type sp,
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:
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
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
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.
[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 were misspecified 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
[virtual]
(virtual protected member function) [edit]
[virtual]
(virtual protected member function of
std::basic_filebuf<CharT,Traits>) [edit]