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| <h4 class="subsection">25.6.3 Cleanups on Exit</h4> |
| |
| <p>Your program can arrange to run its own cleanup functions if normal |
| termination happens. If you are writing a library for use in various |
| application programs, then it is unreliable to insist that all |
| applications call the library's cleanup functions explicitly before |
| exiting. It is much more robust to make the cleanup invisible to the |
| application, by setting up a cleanup function in the library itself |
| using <code>atexit</code> or <code>on_exit</code>. |
| |
| <!-- stdlib.h --> |
| <!-- ISO --> |
| <div class="defun"> |
| — Function: int <b>atexit</b> (<var>void </var>(<var>*function</var>) (<var>void</var>))<var><a name="index-atexit-3139"></a></var><br> |
| <blockquote><p>The <code>atexit</code> function registers the function <var>function</var> to be |
| called at normal program termination. The <var>function</var> is called with |
| no arguments. |
| |
| <p>The return value from <code>atexit</code> is zero on success and nonzero if |
| the function cannot be registered. |
| </p></blockquote></div> |
| |
| <!-- stdlib.h --> |
| <!-- SunOS --> |
| <div class="defun"> |
| — Function: int <b>on_exit</b> (<var>void </var>(<var>*function</var>)(<var>int status, void *arg</var>)<var>, void *arg</var>)<var><a name="index-on_005fexit-3140"></a></var><br> |
| <blockquote><p>This function is a somewhat more powerful variant of <code>atexit</code>. It |
| accepts two arguments, a function <var>function</var> and an arbitrary |
| pointer <var>arg</var>. At normal program termination, the <var>function</var> is |
| called with two arguments: the <var>status</var> value passed to <code>exit</code>, |
| and the <var>arg</var>. |
| |
| <p>This function is included in the GNU C library only for compatibility |
| for SunOS, and may not be supported by other implementations. |
| </p></blockquote></div> |
| |
| <p>Here's a trivial program that illustrates the use of <code>exit</code> and |
| <code>atexit</code>: |
| |
| <pre class="smallexample"> #include <stdio.h> |
| #include <stdlib.h> |
| |
| void |
| bye (void) |
| { |
| puts ("Goodbye, cruel world...."); |
| } |
| |
| int |
| main (void) |
| { |
| atexit (bye); |
| exit (EXIT_SUCCESS); |
| } |
| </pre> |
| <p class="noindent">When this program is executed, it just prints the message and exits. |
| |
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