memmem - locate a substring

#define _GNU_SOURCE /* See feature_test_macros(7) */
#include <string.h>
void *memmem(const void haystack[.haystacklen], size_t haystacklen,
 const void needle[.needlelen], size_t needlelen);

The memmem() function finds the start of the first occurrence of the substring needle of length needlelen in the memory area haystack of length haystacklen.

The memmem() function returns a pointer to the beginning of the substring, or NULL if the substring is not found.

bstring(3), strstr(3)