cpp/string/wide/wcsncat

Appends at most wide characters from the wide string pointed to by  to the end of the character string pointed to by, stopping if the null terminator is copied. The wide character replaces the null terminator at the end of. The null terminator is always appended in the end (so the maximum number of wide characters the function may write is ).

The behavior is undefined if the destination array is not large enough for the contents of both and  and the terminating null wide character.

The behavior is undefined if the strings overlap.