wchar_t *wcscat(wchar_t *s1, const wchar_t *s2);
wcscat appends a copy of the wide string pointed to by s2 (including the terminating null wide character) to the end of the wide string pointed to by s1. The initial character of s2 overwrites the null wide character at the end of s1. The behavior of wcscat is undefined if copying takes place between objects that overlap.
wcscat returns the value of s1.