man3/rpmatch.3

   1 .\" Copyright (C) 2006 Justin Pryzby <pryzbyj@justinpryzby.com>
   2 .\"
   3 .\" %%%LICENSE_START(PERMISSIVE_MISC)
   4 .\" Permission is hereby granted, free of charge, to any person obtaining
   5 .\" a copy of this software and associated documentation files (the
   6 .\" "Software"), to deal in the Software without restriction, including
   7 .\" without limitation the rights to use, copy, modify, merge, publish,
   8 .\" distribute, sublicense, and/or sell copies of the Software, and to
   9 .\" permit persons to whom the Software is furnished to do so, subject to
  10 .\" the following conditions:
  11 .\"
  12 .\" The above copyright notice and this permission notice shall be
  13 .\" included in all copies or substantial portions of the Software.
  14 .\"
  15 .\" THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  16 .\" EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  17 .\" MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
  18 .\" IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
  19 .\" CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
  20 .\" TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
  21 .\" SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  22 .\" %%%LICENSE_END
  23 .\"
  24 .\" References:
  25 .\"   glibc manual and source
  26 .\"
  27 .\" 2006-05-19, mtk, various edits and example program
  28 .\"
  29 .TH RPMATCH 3 2021-03-22 "Linux man-pages (unreleased)" "Linux Programmer's Manual"
  30 .SH NAME
  31 rpmatch \- determine if the answer to a question is affirmative or negative
  32 .SH LIBRARY
  33 Standard C library
  34 .RI ( libc ", " \-lc )
  35 .SH SYNOPSIS
  36 .nf
  37 .B #include <stdlib.h>
  38 .PP
  39 .BI "int rpmatch(const char *" response );
  40 .fi
  41 .PP
  42 .RS -4
  43 Feature Test Macro Requirements for glibc (see
  44 .BR feature_test_macros (7)):
  45 .RE
  46 .PP
  47 .BR rpmatch ():
  48 .nf
  49     Since glibc 2.19:
  50         _DEFAULT_SOURCE
  51     Glibc 2.19 and earlier:
  52         _SVID_SOURCE
  53 .fi
  54 .SH DESCRIPTION
  55 .BR rpmatch ()
  56 handles a user response to yes or no questions, with
  57 support for internationalization.
  58 .PP
  59 .I response
  60 should be a null-terminated string containing a
  61 user-supplied response, perhaps obtained with
  62 .BR fgets (3)
  63 or
  64 .BR getline (3).
  65 .PP
  66 The user's language preference is taken into account per the
  67 environment variables
  68 .BR LANG ,
  69 .BR LC_MESSAGES ,
  70 and
  71 .BR LC_ALL ,
  72 if the program has called
  73 .BR setlocale (3)
  74 to effect their changes.
  75 .PP
  76 Regardless of the locale, responses matching
  77 .B \(ha[Yy]
  78 are always accepted as affirmative, and those matching
  79 .B \(ha[Nn]
  80 are always accepted as negative.
  81 .SH RETURN VALUE
  82 After examining
  83 .IR response ,
  84 .BR rpmatch ()
  85 returns 0 for a recognized negative response ("no"), 1
  86 for a recognized positive response ("yes"), and \-1 when the value
  87 of
  88 .I response
  89 is unrecognized.
  90 .SH ERRORS
  91 A return value of \-1 may indicate either an invalid input, or some
  92 other error.
  93 It is incorrect to only test if the return value is nonzero.
  94 .PP
  95 .BR rpmatch ()
  96 can fail for any of the reasons that
  97 .BR regcomp (3)
  98 or
  99 .BR regexec (3)
 100 can fail; the cause of the error
 101 is not available from
 102 .I errno
 103 or anywhere else, but indicates a
 104 failure of the regex engine (but this case is indistinguishable from
 105 that of an unrecognized value of
 106 .IR response ).
 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 rpmatch ()
 119 T}      Thread safety   MT-Safe locale
 120 .TE
 121 .hy
 122 .ad
 123 .sp 1
 124 .SH STANDARDS
 125 .BR rpmatch ()
 126 is not required by any standard,
 127 but available under the GNU C library, FreeBSD, and AIX.
 128 .SH BUGS
 129 The
 130 .BR YESEXPR " and " NOEXPR
 131 of some locales (including "C") only inspect the first character of the
 132 .IR response .
 133 This can mean that "yno" et al. resolve to
 134 .BR 1 .
 135 This is an unfortunate historical side-effect which should be fixed in time
 136 with proper localisation, and should not deter from
 137 .BR rpmatch ()
 138 being the proper way to distinguish between binary answers.
 139 .SH EXAMPLES
 140 The following program displays the results when
 141 .BR rpmatch ()
 142 is applied to the string given in the program's command-line argument.
 143 .PP
 144 .EX
 145 #define _SVID_SOURCE
 146 #include <locale.h>
 147 #include <stdlib.h>
 148 #include <string.h>
 149 #include <stdio.h>
 150
 151 int
 152 main(int argc, char *argv[])
 153 {
 154     if (argc != 2 || strcmp(argv[1], "\-\-help") == 0) {
 155         fprintf(stderr, "%s response\en", argv[0]);
 156         exit(EXIT_FAILURE);
 157     }
 158
 159     setlocale(LC_ALL, "");
 160     printf("rpmatch() returns: %d\en", rpmatch(argv[1]));
 161     exit(EXIT_SUCCESS);
 162 }
 163 .EE
 164 .SH SEE ALSO
 165 .BR fgets (3),
 166 .BR getline (3),
 167 .BR nl_langinfo (3),
 168 .BR regcomp (3),
 169 .BR setlocale (3)