.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)

.\" and Copyright (c) 2008 Linux Foundation, written by Michael Kerrisk

.\"     <mtk.manpages@gmail.com>

.\"

.\" %%%LICENSE_START(VERBATIM)

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.\" manual provided the copyright notice and this permission notice are

.\" preserved on all copies.

.\"

.\" Permission is granted to copy and distribute modified versions of this

.\" manual under the conditions for verbatim copying, provided that the

.\" entire resulting derived work is distributed under the terms of a

.\" permission notice identical to this one.

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.\" Since the Linux kernel and libraries are constantly changing, this

.\" manual page may be incorrect or out-of-date.  The author(s) assume no

.\" responsibility for errors or omissions, or for damages resulting from

.\" the use of the information contained herein.  The author(s) may not

.\" have taken the same level of care in the production of this manual,

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.\" %%%LICENSE_END

.\"

.\" Modified Mon Apr 12 12:49:57 1993, David Metcalfe

.\" Modified Sat Jul 24 18:56:22 1993, Rik Faith (faith@cs.unc.edu)

.\" Modified Wed Feb 20 21:09:36 2002, Ian Redfern (redferni@logica.com)

.\" 2008-07-09, mtk, add rawmemchr()

.\"

.TH MEMCHR 3  2017-09-15 "" "Linux Programmer's Manual"

.SH NAME

memchr, memrchr, rawmemchr \- scan memory for a character

.SH SYNOPSIS

.nf

.B #include <string.h>

.PP

.BI "void *memchr(const void *" s ", int " c ", size_t " n );

.PP

.BI "void *memrchr(const void *" s ", int " c ", size_t " n );

.PP

.BI "void *rawmemchr(const void *" s ", int " c );

.fi

.PP

.in -4n

Feature Test Macro Requirements for glibc (see

.BR feature_test_macros (7)):

.in

.PP

.BR memrchr (),

.BR rawmemchr ():

_GNU_SOURCE

.SH DESCRIPTION

The

.BR memchr ()

function scans the initial

.I n

bytes of the memory

area pointed to by

.I s

for the first instance of

.IR c .

Both

.I c

and the bytes of the memory area pointed to by

.I s

are interpreted as

.IR "unsigned char" .

.PP

The

.BR memrchr ()

function is like the

.BR memchr ()

function,

except that it searches backward from the end of the

.I n

bytes pointed to by

.I s

instead of forward from the beginning.

.PP

The

.BR rawmemchr ()

function is similar to

.BR memchr ():

it assumes (i.e., the programmer knows for certain)

that an instance of

.I c

lies somewhere in the memory area starting at the location pointed to by

.IR s ,

and so performs an optimized search for

.IR c

(i.e., no use of a count argument to limit the range of the search).

If an instance of

.I c

is not found, the results are unpredictable.

The following call is a fast means of locating a string's

terminating null byte:

.PP

.in +4n

.EX

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

.EE

.in

.SH RETURN VALUE

The

.BR memchr ()

and

.BR memrchr ()

functions return a pointer

to the matching byte or NULL if the character does not occur in

the given memory area.

.PP

The

.BR rawmemchr ()

function returns a pointer to the matching byte, if one is found.

If no matching byte is found, the result is unspecified.

.SH VERSIONS

.BR rawmemchr ()

first appeared in glibc in version 2.1.

.PP

.BR memrchr ()

first appeared in glibc in version 2.2.

.SH ATTRIBUTES

For an explanation of the terms used in this section, see

.BR attributes (7).

.TS

allbox;

lbw32 lb lb

l l l.

Interface	Attribute	Value

T{

.BR memchr (),

.BR memrchr (),

.BR rawmemchr ()

T}	Thread safety	MT-Safe

.TE

.SH CONFORMING TO

.BR memchr ():

POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.

.PP

The

.BR memrchr ()

function is a GNU extension, available since glibc 2.1.91.

.PP

The

.BR rawmemchr ()

function is a GNU extension, available since glibc 2.1.

.SH SEE ALSO

.BR bstring (3),

.BR ffs (3),

.BR index (3),

.BR memmem (3),

.BR rindex (3),

.BR strchr (3),

.BR strpbrk (3),

.BR strrchr (3),

.BR strsep (3),

.BR strspn (3),

.BR strstr (3),

.BR wmemchr (3)

.SH COLOPHON

This page is part of release 4.15 of the Linux

.I man-pages

project.

A description of the project,

information about reporting bugs,

and the latest version of this page,

can be found at

\%https://www.kernel.org/doc/man\-pages/.