The wcsstr function is the wide-character equivalent of the strstr
function. It searches for the first occurrence of the wide-character string
needle (without its terminating L'\0' character) as a substring in the
wide-character string haystack.
The wcsstr function returns a pointer to the first occurrence of
needle in haystack. It returns NULL if needle does not
occur as a substring in haystack.
Note the special case: If needle is the empty wide-character string, the
return value is always haystack itself.