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.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
.\" and Copyright (c) 2008 Linux Foundation, written by Michael Kerrisk
.\" <mtk.manpages@gmail.com>
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.\" 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 2021-03-22 "" "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 );
.BI "void *memrchr(const void *" s ", int " c ", size_t " n );
.BI "void *rawmemchr(const void *" s ", int " c );
.fi
.PP
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.PP
.BR memrchr (),
.BR rawmemchr ():
.nf
_GNU_SOURCE
.fi
.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\e0\(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).
.ad l
.nh
.TS
allbox;
lbx lb lb
l l l.
Interface Attribute Value
T{
.BR memchr (),
.BR memrchr (),
.BR rawmemchr ()
T} Thread safety MT-Safe
.TE
.hy
.ad
.sp 1
.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)
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