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	1	.\" Copyright (c) 1990, 1991, 1993
	2	.\" The Regents of the University of California. All rights reserved.
	3	.\"
	4	.\" This code is derived from software contributed to Berkeley by
	5	.\" Chris Torek and the American National Standards Committee X3,
	6	.\" on Information Processing Systems.
	7	.\"
	8	.\" Redistribution and use in source and binary forms, with or without
	9	.\" modification, are permitted provided that the following conditions
	10	.\" are met:
	11	.\" 1. Redistributions of source code must retain the above copyright
	12	.\" notice, this list of conditions and the following disclaimer.
	13	.\" 2. Redistributions in binary form must reproduce the above copyright
	14	.\" notice, this list of conditions and the following disclaimer in the
	15	.\" documentation and/or other materials provided with the distribution.
	16	.\" 4. Neither the name of the University nor the names of its contributors
	17	.\" may be used to endorse or promote products derived from this software
	18	.\" without specific prior written permission.
	19	.\"
	20	.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
	21	.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	22	.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	23	.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
	24	.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
	25	.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
	26	.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
	27	.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
	28	.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
	29	.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
	30	.\" SUCH DAMAGE.
	31	.\"
	32	.\" @(#)atexit.3 8.1 (Berkeley) 6/4/93
	33	.\" $FreeBSD: src/lib/libc/stdlib/atexit.3,v 1.11 2007/01/09 00:28:09 imp Exp $
	34	.\"
	35	.Dd May 20, 2008
	36	.Dt ATEXIT 3
	37	.Os
	38	.Sh NAME
	39	.Nm atexit
	40	.Nd register a function to be called on exit
	41	.Sh SYNOPSIS
	42	.In stdlib.h
	43	.Ft int
	44	.Fn atexit "void (*func)(void)"
	45	#ifdef UNIFDEF_BLOCKS
	46	.Ft int
	47	.Fn atexit_b "void (^block)(void)"
	48	#endif
	49	.Sh DESCRIPTION
	50	The
	51	.Fn atexit
	52	function
	53	registers the function
	54	.Fa func
	55	to be called at program exit, whether via
	56	.Xr exit 3
	57	or via return from the program's
	58	.Fn main .
	59	Functions so registered are called in reverse order;
	60	no arguments are passed.
	61	#ifdef UNIFDEF_BLOCKS
	62	.Pp
	63	The
	64	.Fn atexit_b
	65	function is like
	66	.Fn atexit
	67	except the callback is a block pointer instead of a function pointer.
	68	.Bd -ragged -offset indent
	69	Note: The
	70	.Fn Block_copy
	71	function (defined in
	72	.In Blocks.h )
	73	is used by
	74	.Fn atexit_b
	75	to make a copy of the block, especially for the case when a stack-based
	76	block might go out of scope when the subroutine returns.
	77	.Ed
	78	#endif
	79	.Pp
	80	These callbacks must not call
	81	.Fn exit ;
	82	if it should be necessary to terminate the process while in such a
	83	function, the
	84	.Xr _exit 2
	85	function should be used.
	86	(Alternatively, the callbacks may cause abnormal
	87	process termination, for example by calling
	88	.Xr abort 3 . )
	89	.Pp
	90	At least 32 callbacks can always be registered;
	91	more are allowed as long as sufficient memory can be allocated.
	92	.\" XXX {ATEXIT_MAX} is not implemented yet
	93	.Sh RETURN VALUES
	94	#ifdef UNIFDEF_BLOCKS
	95	.ds ATEXIT_B atexit_b
	96	#endif
	97	.Rv -std atexit \*[ATEXIT_B]
	98	.Sh ERRORS
	99	.Bl -tag -width Er
	100	.It Bq Er ENOMEM
	101	No memory was available to add the function to the list.
	102	The existing list of functions is unmodified.
	103	.El
	104	.Sh SEE ALSO
	105	.Xr exit 3
	106	.Sh STANDARDS
	107	The
	108	.Fn atexit
	109	function
	110	conforms to
	111	.St -isoC .