.\" Copyright (c) 1990, 1991 The Regents of the University of California.
.\" All rights reserved.
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.\" This code is derived from software contributed to Berkeley by
.\" Chris Torek and the American National Standards Committee X3,
.\" on Information Processing Systems.
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.\"	$OpenBSD: atexit.3,v 1.9 2013/06/05 03:39:23 tedu Exp $
.\"
.Dd $Mdocdate: June 5 2013 $
.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 (*function)(void)"
.Sh DESCRIPTION
The
.Fn atexit
function registers the given
.Fa function
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.
At least 32 functions can always be registered,
and more are allowed as long as sufficient memory can be allocated.
.Pp
.Fn atexit
is very difficult to use correctly without creating
.Xr exit 3 Ns -time
races.
Unless absolutely necessary, please avoid using it.
.Sh RETURN VALUES
.Rv -std atexit
.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 -ansiC .