Home Original page

std::codecvt<InternT,ExternT,StateT>::unshift, do_unshift - cppreference.com

From cppreference.com

Defined in header <locale>

public: result unshift( StateT& state, ExternT* to, ExternT* to_end, ExternT*& to_next ) const;

 (1)

protected: virtual result do_unshift( StateT& state, ExternT* to, ExternT* to_end, ExternT*& to_next ) const;

 (2)

1) Public member function, calls the member function do_unshift of the most derived class.

2) If the encoding represented by this codecvt facet is state-dependent, and state represents a conversion state that is not the initial shift state, writes the characters necessary to return to the initial shift state. The characters are written to a character array whose first element is pointed to by to. No more than to_end - to characters are written. The parameter to_next is updated to point one past the last character written.

Return value

A value of type std::codecvt_base::result, indicating the success status as follows:

ok all necessary characters were written. state now represents initial shift state
partial not enough space in the output buffer. to_next == to_end
error an unspecified error has occurred
noconv the encoding is not state-dependent, no termination sequence necessary

Notes

This function is called by std::basic_filebuf::close() and in other situations when finalizing a state-dependent multibyte character sequence.

Example

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 305 C++98 std::codecvt<wchar_t, char, std::mbstate_t>::do_unshift
was required not to write any character 		not required
LWG 380 C++98 the meaning of returning partial was 'more characters need to
be supplied to complete termination', but no character is supplied 		corrected to indicating
insufficient buffer space
LWG 381 C++98 state was not required to be valid, and
error is returned if state is invalid 		state is required to be valid, and
returning error indicates an error
LWG 664 C++98 std::codecvt<char, char, std::mbstate_t>::do_unshift
was required not to write any character 		not required
LWG 665 C++98 std::codecvt<char, char, std::mbstate_t>::do_unshift
was required to return noconv 		not required

See also

converts a wide character to its multibyte representation, given state
(function) [edit]
converts a string from InternT to ExternT, such as when writing to file
(virtual protected member function) [edit]