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  2012-04-16 "" "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 memrchr (),
  50 .BR rawmemchr ():
  51 _GNU_SOURCE
  52 .SH DESCRIPTION
  53 The
  54 .BR memchr ()
  55 function scans the first \fIn\fP bytes of the memory
  56 area pointed to by \fIs\fP for the character \fIc\fP.
  57 The first byte to
  58 match \fIc\fP (interpreted as an unsigned character) stops the operation.
  59 .PP
  60 The
  61 .BR memrchr ()
  62 function is like the
  63 .BR memchr ()
  64 function,
  65 except that it searches backward from the end of the \fIn\fP bytes
  66 pointed to by \fIs\fP instead of forward from the beginning.
  67
  68 The
  69 .BR rawmemchr ()
  70 function is similar to
  71 .BR memchr ():
  72 it assumes (i.e., the programmer knows for certain)
  73 that the character
  74 .I c
  75 lies somewhere in the string
  76 .IR s ,
  77 and so performs an optimized search
  78 for the character
  79 .IR c
  80 (i.e., no use of a count argument argument to limit the range of the search).
  81 If the character
  82 .I c
  83 is not in the string
  84 .IR s ,
  85 then
  86 .BR rawmemchr ()
  87 may proceed to search beyond the end of the string,
  88 and the result is unspecified.
  89 The following call is a fast means of locating a string's
  90 terminating null byte:
  91 .in +4n
  92 .nf
  93
  94 char *p = rawmemchr(s,\ \(aq\\0\(aq);
  95 .fi
  96 .in
  97 .SH "RETURN VALUE"
  98 The
  99 .BR memchr ()
 100 and
 101 .BR memrchr ()
 102 functions return a pointer
 103 to the matching byte or NULL if the character does not occur in
 104 the given memory area.
 105
 106 The
 107 .BR rawmemchr ()
 108 function returns a pointer to the matching byte, if one is found.
 109 If no matching byte is found, the result is unspecified.
 110 .SH VERSIONS
 111 .BR rawmemchr ()
 112 first appeared in glibc in version 2.1.
 113
 114 .BR memrchr ()
 115 first appeared in glibc in version 2.2.
 116 .SH "CONFORMING TO"
 117 The
 118 .BR memchr ()
 119 function conforms to SVr4, 4.3BSD, C89, C99, POSIX.1-2001.
 120
 121 The
 122 .BR memrchr ()
 123 function is a GNU extension, available since glibc 2.1.91.
 124
 125 The
 126 .BR rawmemchr ()
 127 function is a GNU extension, available since glibc 2.1.
 128 .SH "SEE ALSO"
 129 .BR ffs (3),
 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)