The index function locates the first occurrence of c (converted to a
.Vt char ) in the string pointed to by s. The terminating null character is considered part of the string; therefore if c is \0, the functions locate the terminating \0.
The rindex function is identical to index, except it locates the last occurrence of c.
The functions index and rindex return a pointer to the located character, or NULL if the character does not appear in the string.
memchr(3), strchr(3), strcspn(3), strpbrk(3), strrchr(3), strsep(3), strspn(3), strstr(3), strtok(3)