utf8Strlen
Computes the length of the string in characters, not including the terminating nul character. If the @max'th byte falls in the middle of a character, the last (partial) character is not counted.
Return
the length of the string in characters
Parameters
p
pointer to the start of a UTF-8 encoded string
max
the maximum number of bytes to examine. If @max is less than 0, then the string is assumed to be nul-terminated. If @max is 0, @p will not be examined and may be null. If @max is greater than 0, up to @max bytes are examined