wchar_t *wmempcpy(wchar_t *s1, const wchar_t *s2, size_t n);
wmempcpy copies n wide characters from the object pointed to by s2 into the object pointed to by s1. The behavior of wmempcpy is undefined if copying takes place between objects that overlap.
wmempcpy returns it returns a pointer to the wide character following the last written wide character.
This is an extension found in GNU libc.