.\" Copyright (C) 2006 Justin Pryzby <pryzbyj@justinpryzby.com>
.\"
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.\" References:
.\"   glibc manual and source
.\"
.\" 2006-05-19, mtk, various edits and example program
.\"
.TH RPMATCH 3 2020-06-09 "GNU" "Linux Programmer's Manual"
.SH NAME
rpmatch \- determine if the answer to a question is affirmative or negative
.SH SYNOPSIS
.nf
.B #include <stdlib.h>
.PP
.BI "int rpmatch(const char *" response );
.fi
.PP
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.PP
.BR rpmatch ():
    Since glibc 2.19:
        _DEFAULT_SOURCE
    Glibc 2.19 and earlier:
        _SVID_SOURCE
.SH DESCRIPTION
.BR rpmatch ()
handles a user response to yes or no questions, with
support for internationalization.
.PP
.I response
should be a null-terminated string containing a
user-supplied response, perhaps obtained with
.BR fgets (3)
or
.BR getline (3).
.PP
The user's language preference is taken into account per the
environment variables
.BR LANG ,
.BR LC_MESSAGES ,
and
.BR LC_ALL ,
if the program has called
.BR setlocale (3)
to effect their changes.
.PP
Regardless of the locale, responses matching
.B \(ha[Yy]
are always accepted as affirmative, and those matching
.B \(ha[Nn]
are always accepted as negative.
.SH RETURN VALUE
After examining
.IR response ,
.BR rpmatch ()
returns 0 for a recognized negative response ("no"), 1
for a recognized positive response ("yes"), and \-1 when the value
of
.I response
is unrecognized.
.SH ERRORS
A return value of \-1 may indicate either an invalid input, or some
other error.
It is incorrect to only test if the return value is nonzero.
.PP
.BR rpmatch ()
can fail for any of the reasons that
.BR regcomp (3)
or
.BR regexec (3)
can fail; the cause of the error
is not available from
.I errno
or anywhere else, but indicates a
failure of the regex engine (but this case is indistinguishable from
that of an unrecognized value of
.IR response ).
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lb lb lb
l l l.
Interface	Attribute	Value
T{
.BR rpmatch ()
T}	Thread safety	MT-Safe locale
.TE
.sp 1
.SH CONFORMING TO
.BR rpmatch ()
is not required by any standard, but
is available on a few other systems.
.\" It is available on at least AIX 5.1 and FreeBSD 6.0.
.SH BUGS
The
.BR rpmatch ()
implementation looks at only the first character
of
.IR response .
As a consequence, "nyes" returns 0, and
"ynever; not in a million years" returns 1.
It would be preferable to accept input strings much more
strictly, for example (using the extended regular
expression notation described in
.BR regex (7)):
.B \(ha([yY]|yes|YES)$
and
.BR \(ha([nN]|no|NO)$ .
.SH EXAMPLES
The following program displays the results when
.BR rpmatch ()
is applied to the string given in the program's command-line argument.
.PP
.EX
#define _SVID_SOURCE
#include <locale.h>
#include <stdlib.h>
#include <string.h>
#include <stdio.h>

int
main(int argc, char *argv[])
{
    if (argc != 2 || strcmp(argv[1], "\-\-help") == 0) {
        fprintf(stderr, "%s response\en", argv[0]);
        exit(EXIT_FAILURE);
    }

    setlocale(LC_ALL, "");
    printf("rpmatch() returns: %d\en", rpmatch(argv[1]));
    exit(EXIT_SUCCESS);
}
.EE
.SH SEE ALSO
.BR fgets (3),
.BR getline (3),
.BR nl_langinfo (3),
.BR regcomp (3),
.BR setlocale (3)
.SH COLOPHON
This page is part of release 5.10 of the Linux
.I man-pages
project.
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
\%https://www.kernel.org/doc/man\-pages/.