memchr, memrchr, rawmemchr — scan memory for a character


#include <string.h>
void *memchr( const void *s,
  int c,
  size_t n);
void *memrchr( const void *s,
  int c,
  size_t n);
void *rawmemchr( const void *s,
  int c);
[Note] Note
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
memrchr(), rawmemchr():


The memchr() function scans the initial n bytes of the memory area pointed to by s for the first instance of c. Both c and the bytes of the memory area pointed to by s are interpreted as unsigned char.

The memrchr() function is like the memchr() function, except that it searches backward from the end of the n bytes pointed to by s instead of forward from the beginning.

The rawmemchr() function is similar to memchr(): it assumes (i.e., the programmer knows for certain) that an instance of c lies somewhere in the memory area starting at the location pointed to by s, and so performs an optimized search for c (i.e., no use of a count argument to limit the range of the search). If an instance of c is not found, the results are unpredictable. The following call is a fast means of locating a string's terminating null byte:

char *p = rawmemchr(s, '\0');


The memchr() and memrchr() functions return a pointer to the matching byte or NULL if the character does not occur in the given memory area.

The rawmemchr() function returns a pointer to the matching byte, if one is found. If no matching byte is found, the result is unspecified.


rawmemchr() first appeared in glibc in version 2.1.

memrchr() first appeared in glibc in version 2.2.


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

Interface Attribute Value
memchr(), memrchr(), rawmemchr() Thread safety MT-Safe


memchr(): POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.

The memrchr() function is a GNU extension, available since glibc 2.1.91.

The rawmemchr() function is a GNU extension, available since glibc 2.1.


bstring(3), ffs(3), index(3), memmem(3), rindex(3), strchr(3), strpbrk(3), strrchr(3), strsep(3), strspn(3), strstr(3), wmemchr(3)


This page is part of release 5.11 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−pages/.

  Copyright 1993 David Metcalfe (
and Copyright (c) 2008 Linux Foundation, written by Michael Kerrisk

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Modified Mon Apr 12 12:49:57 1993, David Metcalfe
Modified Sat Jul 24 18:56:22 1993, Rik Faith (
Modified Wed Feb 20 21:09:36 2002, Ian Redfern (
2008-07-09, mtk, add rawmemchr()