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.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.\" References consulted:
.\"     Linux libc source code
.\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
.\"     386BSD man pages
.\" Modified 1993-04-02, David Metcalfe
.\" Modified 1993-07-25, Rik Faith (faith@cs.unc.edu)
.TH ON_EXIT 3  2021-03-22 "Linux man-pages (unreleased)" "Linux Programmer's Manual"
.SH NAME
on_exit \- register a function to be called at normal process termination
.SH LIBRARY
Standard C library
.RI ( libc ", " \-lc )
.SH SYNOPSIS
.nf
.B #include <stdlib.h>
.PP
.BI "int on_exit(void (*" function ")(int, void *), void *" arg );
.fi
.PP
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.PP
.BR on_exit ():
.nf
    Since glibc 2.19:
        _DEFAULT_SOURCE
    Glibc 2.19 and earlier:
        _BSD_SOURCE || _SVID_SOURCE
.fi
.SH DESCRIPTION
The
.BR on_exit ()
function registers the given
.I function
to be
called at normal process termination, whether via
.BR exit (3)
or via return from the program's
.IR main ().
The
.I function
is passed the status argument given to the last call to
.BR exit (3)
and the
.I arg
argument from
.BR on_exit ().
.PP
The same function may be registered multiple times:
it is called once for each registration.
.PP
When a child process is created via
.BR fork (2),
it inherits copies of its parent's registrations.
Upon a successful call to one of the
.BR exec (3)
functions, all registrations are removed.
.SH RETURN VALUE
The
.BR on_exit ()
function returns the value 0 if successful; otherwise
it returns a nonzero value.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.ad l
.nh
.TS
allbox;
lbx lb lb
l l l.
Interface	Attribute	Value
T{
.BR on_exit ()
T}	Thread safety	MT-Safe
.TE
.hy
.ad
.sp 1
.SH STANDARDS
This function comes from SunOS 4, but is also present in glibc.
It no longer occurs in Solaris (SunOS 5).
Portable application should avoid this function, and use the standard
.BR atexit (3)
instead.
.SH NOTES
By the time
.I function
is executed, stack
.RI ( auto )
variables may already have gone out of scope.
Therefore,
.I arg
should not be a pointer to a stack variable;
it may however be a pointer to a heap variable or a global variable.
.SH SEE ALSO
.BR _exit (2),
.BR atexit (3),
.BR exit (3)