wchar_t *wcsncpy(wchar_t *s1, const wchar_t *s2, size_t n);
wcsncpy copies not more than n wide characters from the array pointed to by s2 to the array pointed to by s1. Wide characters that follow a null wide character in s2 are not copied. The behavior of wcsncpy is undefined if copying takes place between objects that overlap. If the array pointed to by s2 is a wide string that is shorter than n wide characters, null wide characters are appended to the copy in the array pointed to by s1, until n characters in all have been written.
wcsncpy returns the value of s1.