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>
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  25 .\" Modified Mon Apr 12 12:49:57 1993, David Metcalfe
  26 .\" Modified Sat Jul 24 18:56:22 1993, Rik Faith (faith@cs.unc.edu)
  27 .\" Modified Wed Feb 20 21:09:36 2002, Ian Redfern (redferni@logica.com)
  28 .\" 2008-07-09, mtk, add rawmemchr()
  29 .\"
  30 .TH MEMCHR 3  2008-08-11 "" "Linux Programmer's Manual"
  31 .SH NAME
  32 memchr, memrchr, rawmemchr \- scan memory for a character
  33 .SH SYNOPSIS
  34 .nf
  35 .B #include <string.h>
  36
  37 .BI "void *memchr(const void *" s ", int " c ", size_t " n );
  38
  39 .BI "void *memrchr(const void *" s ", int " c ", size_t " n );
  40
  41 .BI "void *rawmemchr(const void *" s ", int " c );
  42 .fi
  43 .sp
  44 .in -4n
  45 Feature Test Macro Requirements for glibc (see
  46 .BR feature_test_macros (7)):
  47 .in
  48 .sp
  49 .BR rawmemchr ():
  50 _GNU_SOURCE
  51 .SH DESCRIPTION
  52 The
  53 .BR memchr ()
  54 function scans the first \fIn\fP bytes of the memory
  55 area pointed to by \fIs\fP for the character \fIc\fP.
  56 The first byte to
  57 match \fIc\fP (interpreted as an unsigned character) stops the operation.
  58 .PP
  59 The
  60 .BR memrchr ()
  61 function is like the
  62 .BR memchr ()
  63 function,
  64 except that it searches backwards from the end of the \fIn\fP bytes
  65 pointed to by \fIs\fP instead of forwards from the beginning.
  66
  67 The
  68 .BR rawmemchr ()
  69 function is similar to
  70 .BR memchr ():
  71 it assumes (i.e., the programmer knows for certain)
  72 that the character
  73 .I c
  74 lies somewhere in the string
  75 .IR s ,
  76 and so performs an optimized search
  77 for the character
  78 .IR c
  79 (i.e., no checking for the terminating null byte, or use of an argument,
  80 .IR n ,
  81 to limit the range of the search).
  82 If the character
  83 .I c
  84 is not in the string
  85 .IR s ,
  86 then
  87 .BR rawmemchr ()
  88 may proceeed to search beyond the end of the string,
  89 and the result is unspecified.
  90 The folowing call is a fast means of locating a string's
  91 terminating null byte:
  92 .in +4n
  93 .nf
  94
  95 char *p = rawmemchr(s,\ \(aq\\0\(aq);
  96 .fi
  97 .in
  98 .SH "RETURN VALUE"
  99 The
 100 .BR memchr ()
 101 and
 102 .BR memrchr ()
 103 functions return a pointer
 104 to the matching byte or NULL if the character does not occur in
 105 the given memory area.
 106
 107 The
 108 .BR rawmemchr ()
 109 function returns a pointer to the matching byte, if one is found.
 110 If no matching byte is found, the result is unspecified.
 111 .SH VERSIONS
 112 .BR rawmemchr ()
 113 first appeared in glibc in version 2.1.
 114
 115 .BR memrchr ()
 116 first appeared in glibc in version 2.2.
 117 .SH "CONFORMING TO"
 118 The
 119 .BR memchr ()
 120 function conforms to SVr4, 4.3BSD, C89, C99, POSIX.1-2001.
 121
 122 The
 123 .BR memrchr ()
 124 function is a GNU extension, available since glibc 2.1.91.
 125
 126 The
 127 .BR rawmemchr ()
 128 function is a GNU extension, available since glibc 2.1.
 129 .SH "SEE ALSO"
 130 .BR index (3),
 131 .BR rindex (3),
 132 .BR strchr (3),
 133 .BR strpbrk (3),
 134 .BR strrchr (3),
 135 .BR strsep (3),
 136 .BR strspn (3),
 137 .BR strstr (3),
 138 .BR wmemchr (3)