Match a string against a regular expression
Integer_Type string_match(String_Type str, String_Type pat, Integer_Type pos)
The string_match function returns zero if str does not
match regular expression specified by pat. This function
performs the match starting at position pos (numbered from 1) in
str. This function returns the position of the start of the
match. To find the exact substring actually matched, use
string_match_nth.
string_match_nth, strcmp, strncmp