memmem — locate a substring


#define _GNU_SOURCE         /* See feature_test_macros(7) */
#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.

Return Value

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


For an explanation of the terms used in this section, see attributes(7).

Interface Attribute Value
memmem() Thread safety MT-Safe

Conforming to

This function is not specified in POSIX.1, but is present on a number of other systems.


In glibc 2.0, if needle is empty, memmem() returns a pointer to the last byte of haystack. This is fixed in glibc 2.1.

See Also

bstring(3), strstr(3)


This page is part of release 5.04 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at

Referenced By

bstring(3), memchr(3), strnstr.3bsd(3), strstr(3).

2017-03-13 GNU Linux Programmer's Manual