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authorupstream source tree <ports@midipix.org>2015-03-15 20:14:05 -0400
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+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
+<html xmlns="http://www.w3.org/1999/xhtml"><head><title>Termination</title><meta name="generator" content="DocBook XSL-NS Stylesheets V1.76.1"/><meta name="keywords" content="&#10; ISO C++&#10; , &#10; library&#10; "/><link rel="home" href="../spine.html" title="The GNU C++ Library"/><link rel="up" href="support.html" title="Chapter 4.  Support"/><link rel="prev" href="dynamic_memory.html" title="Dynamic Memory"/><link rel="next" href="diagnostics.html" title="Chapter 5.  Diagnostics"/></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Termination</th></tr><tr><td align="left"><a accesskey="p" href="dynamic_memory.html">Prev</a> </td><th width="60%" align="center">Chapter 4. 
+ Support
+
+</th><td align="right"> <a accesskey="n" href="diagnostics.html">Next</a></td></tr></table><hr/></div><div class="section" title="Termination"><div class="titlepage"><div><div><h2 class="title"><a id="std.support.termination"/>Termination</h2></div></div></div><div class="section" title="Termination Handlers"><div class="titlepage"><div><div><h3 class="title"><a id="support.termination.handlers"/>Termination Handlers</h3></div></div></div><p>
+ Not many changes here to <code class="filename">cstdlib</code>. You should note that the
+ <code class="function">abort()</code> function does not call the
+ destructors of automatic nor static objects, so if you're
+ depending on those to do cleanup, it isn't going to happen.
+ (The functions registered with <code class="function">atexit()</code>
+ don't get called either, so you can forget about that
+ possibility, too.)
+ </p><p>
+ The good old <code class="function">exit()</code> function can be a bit
+ funky, too, until you look closer. Basically, three points to
+ remember are:
+ </p><div class="orderedlist"><ol class="orderedlist"><li class="listitem"><p>
+ Static objects are destroyed in reverse order of their creation.
+ </p></li><li class="listitem"><p>
+ Functions registered with <code class="function">atexit()</code> are called in
+ reverse order of registration, once per registration call.
+ (This isn't actually new.)
+ </p></li><li class="listitem"><p>
+ The previous two actions are <span class="quote">“<span class="quote">interleaved,</span>”</span> that is,
+ given this pseudocode:
+ </p><pre class="programlisting">
+ extern "C or C++" void f1 (void);
+ extern "C or C++" void f2 (void);
+
+ static Thing obj1;
+ atexit(f1);
+ static Thing obj2;
+ atexit(f2);
+</pre><p>
+ then at a call of <code class="function">exit()</code>,
+ <code class="varname">f2</code> will be called, then
+ <code class="varname">obj2</code> will be destroyed, then
+ <code class="varname">f1</code> will be called, and finally
+ <code class="varname">obj1</code> will be destroyed. If
+ <code class="varname">f1</code> or <code class="varname">f2</code> allow an
+ exception to propagate out of them, Bad Things happen.
+ </p></li></ol></div><p>
+ Note also that <code class="function">atexit()</code> is only required to store 32
+ functions, and the compiler/library might already be using some of
+ those slots. If you think you may run out, we recommend using
+ the <code class="function">xatexit</code>/<code class="function">xexit</code> combination from <code class="literal">libiberty</code>, which has no such limit.
+ </p></div><div class="section" title="Verbose Terminate Handler"><div class="titlepage"><div><div><h3 class="title"><a id="support.termination.verbose"/>Verbose Terminate Handler</h3></div></div></div><p>
+ If you are having difficulty with uncaught exceptions and want a
+ little bit of help debugging the causes of the core dumps, you can
+ make use of a GNU extension, the verbose terminate handler.
+ </p><pre class="programlisting">
+#include &lt;exception&gt;
+
+int main()
+{
+ std::set_terminate(__gnu_cxx::__verbose_terminate_handler);
+ ...
+
+ throw <em class="replaceable"><code>anything</code></em>;
+}
+</pre><p>
+ The <code class="function">__verbose_terminate_handler</code> function
+ obtains the name of the current exception, attempts to demangle
+ it, and prints it to stderr. If the exception is derived from
+ <code class="classname">exception</code> then the output from
+ <code class="function">what()</code> will be included.
+ </p><p>
+ Any replacement termination function is required to kill the
+ program without returning; this one calls abort.
+ </p><p>
+ For example:
+ </p><pre class="programlisting">
+#include &lt;exception&gt;
+#include &lt;stdexcept&gt;
+
+struct argument_error : public std::runtime_error
+{
+ argument_error(const std::string&amp; s): std::runtime_error(s) { }
+};
+
+int main(int argc)
+{
+ std::set_terminate(__gnu_cxx::__verbose_terminate_handler);
+ if (argc &gt; 5)
+ throw argument_error(<span class="quote">“<span class="quote">argc is greater than 5!</span>”</span>);
+ else
+ throw argc;
+}
+</pre><p>
+ With the verbose terminate handler active, this gives:
+ </p><pre class="screen">
+ <code class="computeroutput">
+ % ./a.out
+ terminate called after throwing a `int'
+ Aborted
+ % ./a.out f f f f f f f f f f f
+ terminate called after throwing an instance of `argument_error'
+ what(): argc is greater than 5!
+ Aborted
+ </code>
+ </pre><p>
+ The 'Aborted' line comes from the call to
+ <code class="function">abort()</code>, of course.
+ </p><p>
+ This is the default termination handler; nothing need be done to
+ use it. To go back to the previous <span class="quote">“<span class="quote">silent death</span>”</span>
+ method, simply include <code class="filename">exception</code> and
+ <code class="filename">cstdlib</code>, and call
+ </p><pre class="programlisting">
+ std::set_terminate(std::abort);
+ </pre><p>
+ After this, all calls to <code class="function">terminate</code> will use
+ <code class="function">abort</code> as the terminate handler.
+ </p><p>
+ Note: the verbose terminate handler will attempt to write to
+ stderr. If your application closes stderr or redirects it to an
+ inappropriate location,
+ <code class="function">__verbose_terminate_handler</code> will behave in
+ an unspecified manner.
+ </p></div></div><div class="navfooter"><hr/><table width="100%" summary="Navigation footer"><tr><td align="left"><a accesskey="p" href="dynamic_memory.html">Prev</a> </td><td align="center"><a accesskey="u" href="support.html">Up</a></td><td align="right"> <a accesskey="n" href="diagnostics.html">Next</a></td></tr><tr><td align="left" valign="top">Dynamic Memory </td><td align="center"><a accesskey="h" href="../spine.html">Home</a></td><td align="right" valign="top"> Chapter 5. 
+ Diagnostics
+
+</td></tr></table></div></body></html>