# std::codecvt<InternT,ExternT,StateT>::unshift, do_unshift

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< cpp‎ | locale‎ | codecvt

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

| This section is incomplete Reason: no 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

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

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