| .\" 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) |
| .\" Permission is granted to make and distribute verbatim copies of this |
| .\" 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. |
| .\" |
| .\" 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| .\" manual page may be incorrect or out-of-date.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 |
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| .\" 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) |