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

The rindex function locates the position of the last occurrence of the substring subs in the string s, 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, rindex returns 0. If no match is found for subs in s, rindex returns -1.