memmem - Man Page

locate a substring


Standard C library (libc, -lc)


#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.

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).

memmem()Thread safetyMT-Safe


This function is not specified in POSIX.1, but is present on a number of other systems, including: musl libc 0.9.7; FreeBSD 6.0, OpenBSD 5.4, NetBSD, and Illumos.


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)

Referenced By

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

2022-12-15 Linux man-pages 6.02