wcsnlen - determine the length of a fixed-size wide-character string
s, size_t maxlen);
The wcsnlen function is the wide-character equivalent
of the strnlen function. It returns the number of
wide-characters in the string pointed to by s, not
including the terminating L'0' character, but at most
maxlen. In doing this, wcsnlen looks only at
the first maxlen wide-characters at s and
never beyond s+maxlen.
The wcsnlen function returns wcslen(s), if
that is less than maxlen, or maxlen if there
is no L'0' character among the first maxlen wide
characters pointed to by s.
This function is a GNU extension.