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<a name="on_005fexit_002d_002d_002drequest-execution-of-function-with-argument-at-program-exit"></a>
<h3 class="section">2.31 <code>on_exit</code>&mdash;request execution of function with argument at program exit</h3>
<a name="index-on_005fexit"></a>
<p><strong>Synopsis</strong>
</p><div class="example">
<pre class="example">#include &lt;stdlib.h&gt;
int on_exit (void (*<var>function</var>)(int, void *), void *<var>arg</var>);

</pre></div>
<p><strong>Description</strong><br>
You can use <code>on_exit</code> to enroll functions in a list of functions that
will be called when your program terminates normally.  The argument is
a pointer to a user-defined function which takes two arguments.  The
first is the status code passed to exit and the second argument is of type
pointer to void.  The function must not return a result.  The value
of <var>arg</var> is registered and passed as the argument to <var>function</var>.
</p>
<p>The functions are kept in a LIFO stack; that is, the last function
enrolled by <code>atexit</code> or <code>on_exit</code> will be the first to execute when 
your program exits.  You can intermix functions using <code>atexit</code> and
<code>on_exit</code>.
</p>
<p>There is no built-in limit to the number of functions you can enroll
in this list; however, after every group of 32 functions is enrolled,
<code>atexit</code>/<code>on_exit</code> will call <code>malloc</code> to get space for the next part 
of the list.   The initial list of 32 functions is statically allocated, so
you can always count on at least that many slots available.
</p>
<br>
<p><strong>Returns</strong><br>
<code>on_exit</code> returns <code>0</code> if it succeeds in enrolling your function,
<code>-1</code> if it fails (possible only if no space was available for
<code>malloc</code> to extend the list of functions).
</p>
<br>
<p><strong>Portability</strong><br>
<code>on_exit</code> is a non-standard glibc extension
</p>
<p>Supporting OS subroutines required: None
</p>
<br>


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