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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	.\" 3. 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	.\" $FreeBSD$
	34	.\"
	35	.Dd September 6, 2002
	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 (*function)(void)"
	45	#ifdef UNIFDEF_BLOCKS
	46	.Ft int
	47	.Fn atexit_b "void (^function)(void)"
	48	#endif
	49	.Sh DESCRIPTION
	50	The
	51	.Fn atexit
	52	function
	53	registers the given
	54	.Fa function
	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	.Pp
	62	If the provided
	63	.Fa function
	64	is located in a library that has been dynamically loaded (e.g. by
	65	.Fn dlopen ) Ns ,
	66	it will be called when the library is unloaded (due to a call
	67	to
	68	.Fn dlclose )
	69	or at program exit.
	70	#ifdef UNIFDEF_BLOCKS
	71	.Pp
	72	The
	73	.Fn atexit_b
	74	function is like
	75	.Fn atexit
	76	except the callback is a block pointer instead of a function pointer.
	77	.Bd -ragged -offset indent
	78	Note: The
	79	.Fn Block_copy
	80	function (defined in
	81	.In Blocks.h )
	82	is used by
	83	.Fn atexit_b
	84	to make a copy of the block, especially for the case when a stack-based
	85	block might go out of scope when the subroutine returns.
	86	.Ed
	87	#endif
	88	.Pp
	89	These functions must not call
	90	.Fn exit ;
	91	if it should be necessary to terminate the process while in such a
	92	function, the
	93	.Xr _exit 2
	94	function should be used.
	95	(Alternatively, the function may cause abnormal
	96	process termination, for example by calling
	97	.Xr abort 3 . )
	98	.Pp
	99	At least 32 functions can always be registered,
	100	and more are allowed as long as sufficient memory can be allocated.
	101	.\" XXX {ATEXIT_MAX} is not implemented yet
	102	.Sh RETURN VALUES
	103	#ifdef UNIFDEF_BLOCKS
	104	.ds ATEXIT_B atexit_b
	105	#endif
	106	.Rv -std atexit \*[ATEXIT_B]
	107	.Sh ERRORS
	108	.Bl -tag -width Er
	109	.It Bq Er ENOMEM
	110	No memory was available to add the function to the list.
	111	The existing list of functions is unmodified.
	112	.El
	113	.Sh SEE ALSO
	114	.Xr exit 3
	115	.Sh STANDARDS
	116	The
	117	.Fn atexit
	118	function
	119	conforms to
	120	.St -isoC .