mm.c

#include <stdio.h>
#include <stdlib.h>
#include <inttypes.h>
#include <string.h>
int main (void) {
    void * haystack = "abcdaaa";
    void * needle = "aa";
    int m = memmem(haystack, 7, needle, 1  );
    printf("haystack[%lu] needle[%lu] found[%lu]\n",
      haystack,
      needle,
      m );
      char * mm = (char *) memmem(haystack, 7, needle, 1  );
      printf("%c%c%c\n",
        mm, mm+1, mm+2
      );
}