.\" Copyright (c) 1993
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.\" modification, are permitted provided that the following conditions
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.\"	From: @(#)err.3	8.1 (Berkeley) 6/9/93
.\" $FreeBSD: src/lib/libc/gen/err.3,v 1.24 2008/10/31 15:14:40 rwatson Exp $
.\"
.Dd March 6, 1999
.Dt ERR 3
.Os
.Sh NAME
.Nm err ,
.Nm verr ,
.Nm errc ,
.Nm verrc ,
.Nm errx ,
.Nm verrx ,
.Nm warn ,
.Nm vwarn ,
.Nm warnc ,
.Nm vwarnc ,
.Nm warnx ,
.Nm vwarnx ,
.Nm err_set_exit ,
.Nm err_set_file
.Nd formatted error messages
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In err.h
.Ft void
.Fn err "int eval" "const char *fmt" "..."
.Ft void
.Fn err_set_exit "void (*exitf)(int)"
.Ft void
.Fn err_set_file "void *vfp"
.Ft void
.Fn errc "int eval" "int code" "const char *fmt" "..."
.Ft void
.Fn errx "int eval" "const char *fmt" "..."
.Ft void
.Fn warn "const char *fmt" "..."
.Ft void
.Fn warnc "int code" "const char *fmt" "..."
.Ft void
.Fn warnx "const char *fmt" "..."
.In stdarg.h
.Ft void
.Fn verr "int eval" "const char *fmt" "va_list args"
.Ft void
.Fn verrc "int eval" "int code" "const char *fmt" "va_list args"
.Ft void
.Fn verrx "int eval" "const char *fmt" "va_list args"
.Ft void
.Fn vwarn "const char *fmt" "va_list args"
.Ft void
.Fn vwarnc "int code" "const char *fmt" "va_list args"
.Ft void
.Fn vwarnx "const char *fmt" "va_list args"
.Sh DESCRIPTION
The
.Fn err
and
.Fn warn
family of functions display a formatted error message on the standard
error output, or on another file specified using the
.Fn err_set_file
function.
In all cases, the last component of the program name, a colon character,
and a space are output.
If the
.Fa fmt
argument is not NULL, the
.Xr printf 3 Ns
-like formatted error message is output.
The output is terminated by a newline character.
.Pp
The
.Fn err ,
.Fn errc ,
.Fn verr ,
.Fn verrc ,
.Fn warn ,
.Fn warnc ,
.Fn vwarn ,
and
.Fn vwarnc
functions append an error message obtained from
.Xr strerror 3
based on a supplied error code value or the global variable
.Va errno ,
preceded by another colon and space unless the
.Fa fmt
argument is
.Dv NULL .
.Pp
In the case of the
.Fn errc ,
.Fn verrc ,
.Fn warnc ,
and
.Fn vwarnc
functions,
the
.Fa code
argument is used to look up the error message.
.Pp
The
.Fn err ,
.Fn verr ,
.Fn warn ,
and
.Fn vwarn
functions use the global variable
.Va errno
to look up the error message.
.Pp
The
.Fn errx ,
.Fn verrx ,
.Fn warnx ,
and
.Fn vwarnx
functions do not append an error message.
.Pp
The
.Fn err ,
.Fn verr ,
.Fn errc ,
.Fn verrc ,
.Fn errx ,
and
.Fn verrx
functions do not return, but exit with the value of the argument
.Fa eval .
It is recommended that the standard values defined in
.Xr sysexits 3
be used for the value of
.Fa eval .
The
.Fn err_set_exit
function can be used to specify a function which is called before
.Xr exit 3
to perform any necessary cleanup; passing a null function pointer for
.Va exitf
resets the hook to do nothing.
The
.Fn err_set_file
function sets the output stream used by the other functions.
Its
.Fa vfp
argument must be either a pointer to an open stream
(possibly already converted to void *)
or a null pointer
(in which case the output stream is set to standard error).
.Sh EXAMPLES
Display the current
.Va errno
information string and exit:
.Bd -literal -offset indent
if ((p = malloc(size)) == NULL)
	err(EX_OSERR, NULL);
if ((fd = open(file_name, O_RDONLY, 0)) == -1)
	err(EX_NOINPUT, "%s", file_name);
.Ed
.Pp
Display an error message and exit:
.Bd -literal -offset indent
if (tm.tm_hour < START_TIME)
	errx(EX_DATAERR, "too early, wait until %s",
	    start_time_string);
.Ed
.Pp
Warn of an error:
.Bd -literal -offset indent
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(EX_OSFILE, "%s", block_device);
.Ed
.Pp
Warn of an error without using the global variable
.Va errno :
.Bd -literal -offset indent
error = my_function();	/* returns a value from <errno.h> */
if (error != 0)
	warnc(error, "my_function");
.Ed
.Sh SEE ALSO
.Xr exit 3 ,
.Xr fmtmsg 3 ,
.Xr printf 3 ,
.Xr strerror 3 ,
.Xr sysexits 3
.Sh HISTORY
The
.Fn err
and
.Fn warn
functions first appeared in
.Bx 4.4 .
The
.Fn err_set_exit
and
.Fn err_set_file
functions first appeared in
.Fx 2.1 .
The
.Fn errc
and
.Fn warnc
functions first appeared in
.Fx 3.0 .