MEMMEM

memmem − locate a substring

#include <string.h>

void *memmem(const void *haystack, size_t haystacklen,
       const void *needle, 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.

This function is a GNU extension.

This function was broken in Linux libraries up to and including libc 5.0.9; there the ‘needle’ and ‘haystack’ arguments were interchanged, and a pointer to the end of the first occurrence of needle was returned. Since libc 5.0.9 is still widely used, this is a dangerous function to use.
Both old and new libc’s have the bug that if needle is empty haystack-1 (instead of haystack) is returned. And glibc (2.0.5) makes it worse, and returns a pointer to the last byte of ‘haystack’. Hopefully this will be fixed. For the time being, memmem() should not be used with an empty ‘needle’.

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