man3/memchr.3

   1 .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
   2 .\" and Copyright (c) 2008 Linux Foundation, written by Michael Kerrisk
   3 .\"     <mtk.manpages@gmail.com>
   4 .\"
   5 .\" SPDX-License-Identifier: Linux-man-pages-copyleft
   6 .\"
   7 .\" Modified Mon Apr 12 12:49:57 1993, David Metcalfe
   8 .\" Modified Sat Jul 24 18:56:22 1993, Rik Faith (faith@cs.unc.edu)
   9 .\" Modified Wed Feb 20 21:09:36 2002, Ian Redfern (redferni@logica.com)
  10 .\" 2008-07-09, mtk, add rawmemchr()
  11 .\"
  12 .TH memchr 3 (date) "Linux man-pages (unreleased)"
  13 .SH NAME
  14 memchr, memrchr, rawmemchr \- scan memory for a character
  15 .SH LIBRARY
  16 Standard C library
  17 .RI ( libc ", " \-lc )
  18 .SH SYNOPSIS
  19 .nf
  20 .B #include <string.h>
  21 .PP
  22 .BI "void *memchr(const void *" s ", int " c ", size_t " n );
  23 .BI "void *memrchr(const void *" s ", int " c ", size_t " n );
  24 .BI "void *rawmemchr(const void *" s ", int " c );
  25 .fi
  26 .PP
  27 .RS -4
  28 Feature Test Macro Requirements for glibc (see
  29 .BR feature_test_macros (7)):
  30 .RE
  31 .PP
  32 .BR memrchr (),
  33 .BR rawmemchr ():
  34 .nf
  35     _GNU_SOURCE
  36 .fi
  37 .SH DESCRIPTION
  38 The
  39 .BR memchr ()
  40 function scans the initial
  41 .I n
  42 bytes of the memory
  43 area pointed to by
  44 .I s
  45 for the first instance of
  46 .IR c .
  47 Both
  48 .I c
  49 and the bytes of the memory area pointed to by
  50 .I s
  51 are interpreted as
  52 .IR "unsigned char" .
  53 .PP
  54 The
  55 .BR memrchr ()
  56 function is like the
  57 .BR memchr ()
  58 function,
  59 except that it searches backward from the end of the
  60 .I n
  61 bytes pointed to by
  62 .I s
  63 instead of forward from the beginning.
  64 .PP
  65 The
  66 .BR rawmemchr ()
  67 function is similar to
  68 .BR memchr ():
  69 it assumes (i.e., the programmer knows for certain)
  70 that an instance of
  71 .I c
  72 lies somewhere in the memory area starting at the location pointed to by
  73 .IR s ,
  74 and so performs an optimized search for
  75 .I c
  76 (i.e., no use of a count argument to limit the range of the search).
  77 If an instance of
  78 .I c
  79 is not found, the results are unpredictable.
  80 The following call is a fast means of locating a string's
  81 terminating null byte:
  82 .PP
  83 .in +4n
  84 .EX
  85 char *p = rawmemchr(s,\ \(aq\e0\(aq);
  86 .EE
  87 .in
  88 .SH RETURN VALUE
  89 The
  90 .BR memchr ()
  91 and
  92 .BR memrchr ()
  93 functions return a pointer
  94 to the matching byte or NULL if the character does not occur in
  95 the given memory area.
  96 .PP
  97 The
  98 .BR rawmemchr ()
  99 function returns a pointer to the matching byte, if one is found.
 100 If no matching byte is found, the result is unspecified.
 101 .SH VERSIONS
 102 .BR rawmemchr ()
 103 first appeared in glibc in version 2.1.
 104 .PP
 105 .BR memrchr ()
 106 first appeared in glibc in version 2.2.
 107 .SH ATTRIBUTES
 108 For an explanation of the terms used in this section, see
 109 .BR attributes (7).
 110 .ad l
 111 .nh
 112 .TS
 113 allbox;
 114 lbx lb lb
 115 l l l.
 116 Interface       Attribute       Value
 117 T{
 118 .BR memchr (),
 119 .BR memrchr (),
 120 .BR rawmemchr ()
 121 T}      Thread safety   MT-Safe
 122 .TE
 123 .hy
 124 .ad
 125 .sp 1
 126 .SH STANDARDS
 127 .BR memchr ():
 128 POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.
 129 .PP
 130 The
 131 .BR memrchr ()
 132 function is a GNU extension, available since glibc 2.1.91.
 133 .PP
 134 The
 135 .BR rawmemchr ()
 136 function is a GNU extension, available since glibc 2.1.
 137 .SH SEE ALSO
 138 .BR bstring (3),
 139 .BR ffs (3),
 140 .BR index (3),
 141 .BR memmem (3),
 142 .BR rindex (3),
 143 .BR strchr (3),
 144 .BR strpbrk (3),
 145 .BR strrchr (3),
 146 .BR strsep (3),
 147 .BR strspn (3),
 148 .BR strstr (3),
 149 .BR wmemchr (3)