cpp/string/wide/wcsxfrm

Transforms the null-terminated wide string pointed to by into the implementation-defined form such that comparing two transformed strings with std gives the same result as comparing the original strings with std, in the current C locale.

The first characters of the transformed string are written to destination, including the terminating null character, and the length of the full transformed string is returned, excluding the terminating null character.

If is, then  is allowed to be a null pointer.

Return value
The length of the transformed wide string, not including the terminating null-character.