int index(const char *s, const char *subs)
int index(const char *s, const char *subs, int start)

The index function locates the position of the first occurrence of the substring (subs) in the s string, starting at the optional position start. If the specified value of start is less than 0, it is implicitly set to 0. If s is an empty string, index returns 0. If no match is found for subs in s, index returns 1.