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2 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Termination</title><meta name="generator" content="DocBook XSL-NS Stylesheets V1.77.1" /><meta name="keywords" content="ISO C++, library" /><meta name="keywords" content="ISO C++, runtime, library" /><link rel="home" href="../index.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 width="20%" align="left"><a accesskey="p" href="dynamic_memory.html">Prev</a> </td><th width="60%" align="center">Chapter 4.
5 </th><td width="20%" align="right"> <a accesskey="n" href="diagnostics.html">Next</a></td></tr></table><hr /></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="std.support.termination"></a>Termination</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="support.termination.handlers"></a>Termination Handlers</h3></div></div></div><p>
6 Not many changes here to <code class="filename">cstdlib</code>. You should note that the
7 <code class="function">abort()</code> function does not call the
8 destructors of automatic nor static objects, so if you're
9 depending on those to do cleanup, it isn't going to happen.
10 (The functions registered with <code class="function">atexit()</code>
11 don't get called either, so you can forget about that
14 The good old <code class="function">exit()</code> function can be a bit
15 funky, too, until you look closer. Basically, three points to
17 </p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p>
18 Static objects are destroyed in reverse order of their creation.
19 </p></li><li class="listitem"><p>
20 Functions registered with <code class="function">atexit()</code> are called in
21 reverse order of registration, once per registration call.
22 (This isn't actually new.)
23 </p></li><li class="listitem"><p>
24 The previous two actions are <span class="quote">“<span class="quote">interleaved,</span>”</span> that is,
25 given this pseudocode:
26 </p><pre class="programlisting">
27 extern "C or C++" void f1 (void);
28 extern "C or C++" void f2 (void);
35 then at a call of <code class="function">exit()</code>,
36 <code class="varname">f2</code> will be called, then
37 <code class="varname">obj2</code> will be destroyed, then
38 <code class="varname">f1</code> will be called, and finally
39 <code class="varname">obj1</code> will be destroyed. If
40 <code class="varname">f1</code> or <code class="varname">f2</code> allow an
41 exception to propagate out of them, Bad Things happen.
42 </p></li></ol></div><p>
43 Note also that <code class="function">atexit()</code> is only required to store 32
44 functions, and the compiler/library might already be using some of
45 those slots. If you think you may run out, we recommend using
46 the <code class="function">xatexit</code>/<code class="function">xexit</code> combination from <code class="literal">libiberty</code>, which has no such limit.
47 </p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="support.termination.verbose"></a>Verbose Terminate Handler</h3></div></div></div><p>
48 If you are having difficulty with uncaught exceptions and want a
49 little bit of help debugging the causes of the core dumps, you can
50 make use of a GNU extension, the verbose terminate handler.
51 </p><pre class="programlisting">
52 #include <exception>
56 std::set_terminate(__gnu_cxx::__verbose_terminate_handler);
59 throw <em class="replaceable"><code>anything</code></em>;
62 The <code class="function">__verbose_terminate_handler</code> function
63 obtains the name of the current exception, attempts to demangle
64 it, and prints it to stderr. If the exception is derived from
65 <code class="classname">exception</code> then the output from
66 <code class="function">what()</code> will be included.
68 Any replacement termination function is required to kill the
69 program without returning; this one calls abort.
72 </p><pre class="programlisting">
73 #include <exception>
74 #include <stdexcept>
76 struct argument_error : public std::runtime_error
78 argument_error(const std::string& s): std::runtime_error(s) { }
83 std::set_terminate(__gnu_cxx::__verbose_terminate_handler);
85 throw argument_error(<span class="quote">“<span class="quote">argc is greater than 5!</span>”</span>);
90 With the verbose terminate handler active, this gives:
91 </p><pre class="screen">
92 <code class="computeroutput">
94 terminate called after throwing a `int'
96 % ./a.out f f f f f f f f f f f
97 terminate called after throwing an instance of `argument_error'
98 what(): argc is greater than 5!
102 The 'Aborted' line comes from the call to
103 <code class="function">abort()</code>, of course.
105 This is the default termination handler; nothing need be done to
106 use it. To go back to the previous <span class="quote">“<span class="quote">silent death</span>”</span>
107 method, simply include <code class="filename">exception</code> and
108 <code class="filename">cstdlib</code>, and call
109 </p><pre class="programlisting">
110 std::set_terminate(std::abort);
112 After this, all calls to <code class="function">terminate</code> will use
113 <code class="function">abort</code> as the terminate handler.
115 Note: the verbose terminate handler will attempt to write to
116 stderr. If your application closes stderr or redirects it to an
117 inappropriate location,
118 <code class="function">__verbose_terminate_handler</code> will behave in
119 an unspecified manner.
120 </p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="dynamic_memory.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="support.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="diagnostics.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Dynamic Memory </td><td width="20%" align="center"><a accesskey="h" href="../index.html">Home</a></td><td width="40%" align="right" valign="top"> Chapter 5.
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