freebsd-dev/lib/libc/gen/err.3

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.\"	From: @(#)err.3	8.1 (Berkeley) 6/9/93
.\" $FreeBSD$
.\"
.Dd March 29, 2012
.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
and
.Fn warnx
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 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 STANDARDS
The
.Fn err
and
.Fn warn
families of functions are
.Bx
extensions.
As such they should not be used in truly portable code.
Use
.Fn strerror
or similar functions instead.
.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 .