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.\" Copyright (c) 1990, 1991 The Regents of the University of California.
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.\" All rights reserved.
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.\"
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.\" This code is derived from software contributed to Berkeley by
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.\" Chris Torek and the American National Standards Committee X3,
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.\" on Information Processing Systems.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $OpenBSD: atexit.3,v 1.8 2007/05/31 19:19:31 jmc Exp $
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.\"
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.Dd $Mdocdate: May 31 2007 $
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.Dt ATEXIT 3
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.Os
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.Sh NAME
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.Nm atexit
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.Nd register a function to be called on exit
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.Sh SYNOPSIS
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.Fd #include <stdlib.h>
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.Ft int
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.Fn atexit "void (*function)(void)"
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.Sh DESCRIPTION
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The
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.Fn atexit
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function registers the given
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.Fa function
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to be called at program exit, whether via
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.Xr exit 3
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or via return from the program's
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.Fn main .
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Functions so registered are called in reverse order;
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no arguments are passed.
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At least 32 functions can always be registered,
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and more are allowed as long as sufficient memory can be allocated.
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.Pp
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.Fn atexit
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is very difficult to use correctly without creating
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.Xr exit 3 Ns -time
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races.
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Unless absolutely necessary, please avoid using it.
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.Sh RETURN VALUES
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.Rv -std atexit
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.Sh ERRORS
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.Bl -tag -width Er
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.It Bq Er ENOMEM
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No memory was available to add the function to the list.
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The existing list of functions is unmodified.
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.El
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.Sh SEE ALSO
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.Xr exit 3
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.Sh STANDARDS
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The
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.Fn atexit
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function conforms to
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.St -ansiC .
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