mirror of https://github.com/mkerrisk/man-pages
139 lines
3.8 KiB
Groff
139 lines
3.8 KiB
Groff
.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
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.\" and Copyright (c) 2008 Linux Foundation, written by Michael Kerrisk
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.\" <mtk.manpages@gmail.com>
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.\"
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\"
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.\" Modified Mon Apr 12 12:49:57 1993, David Metcalfe
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.\" Modified Sat Jul 24 18:56:22 1993, Rik Faith (faith@cs.unc.edu)
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.\" Modified Wed Feb 20 21:09:36 2002, Ian Redfern (redferni@logica.com)
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.\" 2008-07-09, mtk, add rawmemchr()
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.\"
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.TH MEMCHR 3 2008-08-11 "" "Linux Programmer's Manual"
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.SH NAME
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memchr, memrchr, rawmemchr \- scan memory for a character
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.SH SYNOPSIS
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.nf
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.B #include <string.h>
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.BI "void *memchr(const void *" s ", int " c ", size_t " n );
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.BI "void *memrchr(const void *" s ", int " c ", size_t " n );
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.BI "void *rawmemchr(const void *" s ", int " c );
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.fi
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.sp
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.in -4n
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Feature Test Macro Requirements for glibc (see
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.BR feature_test_macros (7)):
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.in
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.sp
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.BR rawmemchr ():
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_GNU_SOURCE
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.SH DESCRIPTION
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The
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.BR memchr ()
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function scans the first \fIn\fP bytes of the memory
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area pointed to by \fIs\fP for the character \fIc\fP.
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The first byte to
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match \fIc\fP (interpreted as an unsigned character) stops the operation.
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.PP
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The
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.BR memrchr ()
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function is like the
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.BR memchr ()
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function,
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except that it searches backwards from the end of the \fIn\fP bytes
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pointed to by \fIs\fP instead of forwards from the beginning.
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The
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.BR rawmemchr ()
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function is similar to
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.BR memchr ():
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it assumes (i.e., the programmer knows for certain)
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that the character
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.I c
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lies somewhere in the string
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.IR s ,
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and so performs an optimized search
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for the character
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.IR c
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(i.e., no checking for the terminating null byte, or use of an argument,
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.IR n ,
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to limit the range of the search).
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If the chararacter
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.I c
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is not in the string
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.IR s ,
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then
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.BR rawmemchr ()
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may proceeed to search beyond the end of the string,
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and the result is unspecified.
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The folowing call is a fast means of locating a string's
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terminating null byte:
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.in +4n
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.nf
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char *p = rawmemchr(s,\ \(aq\\0\(aq);
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.fi
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.in
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.SH "RETURN VALUE"
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The
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.BR memchr ()
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and
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.BR memrchr ()
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functions return a pointer
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to the matching byte or NULL if the character does not occur in
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the given memory area.
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The
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.BR rawmemchr ()
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function returns a pointer to the matching byte, if one is found.
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If no matching byte is found, the result is unspecified.
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.SH VERSIONS
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.BR rawmemchr ()
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first appeared in glibc in version 2.1.
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.BR memrchr ()
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first appeared in glibc in version 2.2.
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.SH "CONFORMING TO"
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The
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.BR memchr ()
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function conforms to SVr4, 4.3BSD, C89, C99, POSIX.1-2001.
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The
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.BR memrchr ()
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function is a GNU extension, available since glibc 2.1.91.
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The
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.BR rawmemchr ()
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function is a GNU extension, available since glibc 2.1.
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.SH "SEE ALSO"
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.BR index (3),
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.BR rindex (3),
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.BR strchr (3),
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.BR strpbrk (3),
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.BR strrchr (3),
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.BR strsep (3),
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.BR strspn (3),
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.BR strstr (3),
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.BR wmemchr (3)
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