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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=" 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 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 <exception> 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 <exception> #include <stdexcept> struct argument_error : public std::runtime_error { argument_error(const std::string& s): std::runtime_error(s) { } }; int main(int argc) { std::set_terminate(__gnu_cxx::__verbose_terminate_handler); if (argc > 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="../index.html">Home</a></td><td align="right" valign="top"> Chapter 5. Diagnostics </td></tr></table></div></body></html>