.\" Copyright (c) 1990, 1991, 1993
.\"	The Regents of the University of California.  All rights reserved.
.\"
.\" This code is derived from software contributed to Berkeley by
.\" Chris Torek and the American National Standards Committee X3,
.\" on Information Processing Systems.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 4. Neither the name of the University nor the names of its contributors
.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\"     @(#)atexit.3	8.1 (Berkeley) 6/4/93
.\" $FreeBSD: src/lib/libc/stdlib/atexit.3,v 1.11 2007/01/09 00:28:09 imp Exp $
.\"
.Dd May 20, 2008
.Dt ATEXIT 3
.Os
.Sh NAME
.Nm atexit
.Nd register a function to be called on exit
.Sh SYNOPSIS
.In stdlib.h
.Ft int
.Fn atexit "void (*func)(void)"
#ifdef UNIFDEF_BLOCKS
.Ft int
.Fn atexit_b "void (^block)(void)"
#endif
.Sh DESCRIPTION
The
.Fn atexit
function
registers the function
.Fa func
to be called at program exit, whether via
.Xr exit 3
or via return from the program's
.Fn main .
Functions so registered are called in reverse order;
no arguments are passed.
#ifdef UNIFDEF_BLOCKS
.Pp
The
.Fn atexit_b
function is like
.Fn atexit
except the callback is a block pointer instead of a function pointer.
.Bd -ragged -offset indent
Note: The
.Fn Block_copy
function (defined in
.In Blocks.h )
is used by
.Fn atexit_b
to make a copy of the block, especially for the case when a stack-based
block might go out of scope when the subroutine returns.
.Ed
#endif
.Pp
These callbacks must not call
.Fn exit ;
if it should be necessary to terminate the process while in such a
function, the
.Xr _exit 2
function should be used.
(Alternatively, the callbacks may cause abnormal
process termination, for example by calling
.Xr abort 3 . )
.Pp
At least 32 callbacks can always be registered;
more are allowed as long as sufficient memory can be allocated.
.\" XXX {ATEXIT_MAX} is not implemented yet
.Sh RETURN VALUES
#ifdef UNIFDEF_BLOCKS
.ds ATEXIT_B atexit_b
#endif
.Rv -std atexit \*[ATEXIT_B]
.Sh ERRORS
.Bl -tag -width Er
.It Bq Er ENOMEM
No memory was available to add the function to the list.
The existing list of functions is unmodified.
.El
.Sh SEE ALSO
.Xr exit 3
.Sh STANDARDS
The
.Fn atexit
function
conforms to
.St -isoC .