std::basic_filebuf<CharT, Traits>* close();
If a put area exist (e.g. file was opened for writing), first calls overflow(Traits::eof()) to write all pending output to the file, including any unshift sequences.
If the most recently called function, out of
overflow(), then calls std::codecvt::unshift(), perhaps multiple times, to determine the unshift sequence according to the imbued locale, and writes that sequence to file with overflow(Traits::eof()).
Then, closes the file as if by calling std::fclose, regardless of whether any of the preceding calls succeeded or failed.
If any of the function calls made, including the call to std::fclose, fails, returns a null pointer. If any of the function calls made throws an exception, the exception is caught and rethrown after calling std::fclose. If the file is already closed, returns a null pointer right away.
In any case, updates the private member variable that is accessed by
close() is typically called through the destructor of std::basic_filebuf (which, in turn, is typically called by the destructor of std::basic_fstream.
| checks if the associated file is open |