man-pages/man3/rpmatch.3

.\" 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 2007-07-26 "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>

.BI "int rpmatch(const char *" response );
.fi
.sp
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.sp
.BR rpmatch ():
_SVID_SOURCE
.SH DESCRIPTION
.BR rpmatch ()
handles a user response to yes or no questions, with
support for internationalization.

\fIresponse\fP should be a null-terminated string containing a
user-supplied response, perhaps obtained with
.BR fgets (3)
or
.BR getline (3).

The user's language preference is taken into account per the
environment variables \fBLANG\fP, \fBLC_MESSAGES\fP, and \fBLC_ALL\fP,
if the program has called
.BR setlocale (3)
to effect their changes.

Regardless of the locale, responses matching \fB^[Yy]\fP are always
accepted as affirmative, and those matching \fB^[Nn]\fP 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 \fIresponse\fP 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 non-zero.

.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 \fIerrno\fP or anywhere else, but indicates a
failure of the regex engine (but this case is indistinguishable from
that of an unrecognized value of \fIresponse\fP).
.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 \fIresponse\fP.
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)):
\fB^([yY]|yes|YES)$\fP and \fB^([nN]|no|NO)$\fP.
.SH EXAMPLE
The following program displays the results when
.BR rpmatch ()
is applied to the string given in the program's command-line argument.
.nf

#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\\n", argv[0]);
        exit(EXIT_FAILURE);
    }

    setlocale(LC_ALL, "");
    printf("rpmatch() returns: %d\\n", rpmatch(argv[1]));
    exit(EXIT_SUCCESS);
}
.fi
.SH SEE ALSO
.BR fgets (3),
.BR getline (3),
.BR nl_langinfo (3),
.BR regcomp (3),
.BR setlocale (3)