man-pages/man3/atexit.3

.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
.\"
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.\" References consulted:
.\"     Linux libc source code
.\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
.\"     386BSD man pages
.\" Modified 1993-03-29, David Metcalfe
.\" Modified 1993-07-24, Rik Faith (faith@cs.unc.edu)
.\" Modified 2003-10-25, Walter Harms
.\"
.TH ATEXIT 3  2003-11-01 "" "Linux Programmer's Manual"
.SH NAME
atexit \- register a function to be called at normal process termination
.SH SYNOPSIS
.nf
.B #include <stdlib.h>
.sp
.BI "int atexit(void (*" function )(void));
.fi
.SH DESCRIPTION
The
.BR atexit ()
function registers the given \fIfunction\fP to be
called at normal process termination, either via
.BR exit (3)
or via return from the program's \fImain\fP().
Functions so registered are called in
the reverse order of their registration; no arguments are passed.
.LP
POSIX.1-2001 requires that an implementation allow at least ATEXIT_MAX (32)
such functions to be registered.
The actual limit supported by an implementation can be obtained using
.BR sysconf (3).
.LP
When a child process is created via
.BR fork (2),
it inherits copies of its parents registrations.
Upon a successful call to one of the
.BR exec ()
functions,
all registrations are removed.
.SH "RETURN VALUE"
The
.BR atexit ()
function returns the value 0 if successful; otherwise
it returns a non-zero value.
.SH EXAMPLE
.nf
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

void
bye(void)
{
    printf("That was all, folks\en");
}

int
main(void)
{
    long a;
    int i;

    a = sysconf(_SC_ATEXIT_MAX);
    printf("ATEXIT_MAX = %ld\en", a);

    i = atexit(bye);
    if (i != 0) {
       fprintf(stderr, "cannot set exit function\en");
       return EXIT_FAILURE;
    }
    return EXIT_SUCCESS;
}
.fi
.SH NOTES
Since glibc 2.2.3,
.BR atexit ()
(and
.BR on_exit (3))
can be used to within a shared library to establish functions
that are called when the shared library is unloaded.
.PP
Functions registered using
.BR atexit ()
(and
.BR on_exit (3))
are not called if a process terminates abnormally because
of the delivery of a signal.
.SH "CONFORMING TO"
SVr4, 4.3BSD, C89, C99, POSIX.1-2001.
.SH "SEE ALSO"
.BR _exit (3),
.BR exit (3),
.BR on_exit (3)