man-pages/man3/err.3

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.\"	From: @(#)err.3	8.1 (Berkeley) 6/9/93
.\" $FreeBSD: src/lib/libc/gen/err.3,v 1.11.2.5 2001/08/17 15:42:32 ru Exp $
.\"
.\" 2007-12-08, mtk, Converted from mdoc to man macros
.\"
.TH ERR 3 2007-12-28 "Linux" "Linux Programmer's Manual"
.SH NAME
err, verr, errx, verrx, warn, vwarn, warnx, vwarnx \- formatted error messages
.SH SYNOPSIS
.nf
.B #include <err.h>
.sp
.BI "void err(int " eval ", const char *" fmt ", ...);"
.sp
.BI "void errx(int " eval ", const char *" fmt ", ...);"
.sp
.BI "void warn(const char *" fmt ", ...);"
.sp
.BI "void warnx(const char *" fmt ", ...);"
.sp
.B #include <stdarg.h>
.sp
.BI "void verr(int " eval ", const char *" fmt ", va_list " args );
.sp
.BI "void verrx(int " eval ", const char *" fmt ", va_list " args );
.sp
.BI "void vwarn(const char *" fmt ", va_list " args );
.sp
.BI "void vwarnx(const char *" fmt ", va_list " args );
.fi
.SH DESCRIPTION
The
.BR err ()
and
.BR warn ()
family of functions display a formatted error message on the standard
error output.
In all cases, the last component of the program name, a colon character,
and a space are output.
If the
.I fmt
argument is not NULL, the
.BR printf (3)-like
formatted error message is output.
The output is terminated by a newline character.
.PP
The
.BR err (),
.BR verr (),
.BR warn (),
and
.BR vwarn ()
functions append an error message obtained from
.BR strerror (3)
based on a code or the global variable
.IR errno ,
preceded by another colon and space unless the
.I fmt
argument is
NULL.
.PP
The
.BR err (),
.BR verr (),
.BR warn (),
and
.BR vwarn ()
functions use the global variable
.I errno
to look up the error message.
.PP
The
.BR errx ()
and
.BR warnx ()
functions do not append an error message.
.PP
The
.BR err (),
.BR verr (),
.BR errx (),
and
.BR verrx ()
functions do not return, but exit with the value of the argument
.IR eval .
.SH EXAMPLES
Display the current errno information string and exit:
.in +4n
.nf

if ((p = malloc(size)) == NULL)
    err(1, NULL);
if ((fd = open(file_name, O_RDONLY, 0)) == \-1)
    err(1, "%s", file_name);
.fi
.in
.PP
Display an error message and exit:
.in +4n
.nf

if (tm.tm_hour < START_TIME)
    errx(1, "too early, wait until %s", start_time_string);
.fi
.in
.PP
Warn of an error:
.in +4n
.nf

if ((fd = open(raw_device, O_RDONLY, 0)) == \-1)
    warnx("%s: %s: trying the block device",
            raw_device, strerror(errno));
if ((fd = open(block_device, O_RDONLY, 0)) == \-1)
    err(1, "%s", block_device);
.fi
.in
.SH "CONFORMING TO"
These functions are non-standard BSD extensions.
.\" .SH HISTORY
.\" The
.\" .BR err ()
.\" and
.\" .BR warn ()
.\" functions first appeared in
.\" 4.4BSD.
.SH SEE ALSO
.BR error (3),
.BR exit (3),
.BR perror (3),
.BR printf (3),
.BR strerror (3)