2.2.8 void * memmem

void * memmem(const void *, size_t, const void *, size_t) __ATTR_PURE__

The memmem() function finds the start of the first occurrence of the substring s2 of length len2 in the memory area s1 of length len1.

Remember:

The memmem() function returns a pointer to the beginning of the substring, or NULL if the substring is not found. If len2 is zero, the function returns s1.