freebsd/lib/libc/gen/err.3

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.\"	From: @(#)err.3	8.1 (Berkeley) 6/9/93
.\" $FreeBSD$
.\"
.Dd Mar 6, 1999
.Dt ERR 3
.Os BSD 4
.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 SYNOPSIS
.Fd #include <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" "..."
.Fd #include <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
.Va fmt
argument is not NULL, the formatted error message is output.
In the case of the
.Fn errc ,
.Fn verrc ,
.Fn warnc ,
and
.Fn vwarnc
functions,
the error message string affiliated with the
.Va code
argument is also output,
preceded by another colon and space if necessary.
In all cases, the output is followed by a newline character.
.Pp
The
.Fn err ,
.Fn verr ,
.Fn warn ,
and
.Fn vwarn
functions use the global variable
.Va errno
rather than the
.Va code
argument of the
.Fn errc
family
.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 .
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
.Va 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 errno information string and exit:
.Bd -literal -offset indent
if ((p = malloc(size)) == NULL)
	err(1, NULL);
if ((fd = open(file_name, O_RDONLY, 0)) == -1)
	err(1, "%s", file_name);
.Ed
.Pp
Display an error message and exit:
.Bd -literal -offset indent
if (tm.tm_hour < START_TIME)
	errx(1, "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(1, "%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 strerror 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 .