libstdc++-v3/doc/html/manual/termination.html - gcc - Git at Google

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   Support

 </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>
       Not many changes here to
       <code class="filename">&lt;cstdlib&gt;</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" type="1"><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 ();
   extern "C or C++" void f2 ();

   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"><div class="titlepage"><div><div><h3 class="title"><a id="support.termination.verbose"></a>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><p>
       The verbose terminate handler is only available for hosted environments
       (see <a class="xref" href="configure.html" title="Configure">Configuring</a>) and will be used
       by default unless the library is built with
       <code class="option">--disable-libstdcxx-verbose</code>
       or with exceptions disabled.
       If you need to enable it explicitly you can do so by calling the
       <code class="function">std::set_terminate</code> function.
     </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 <code class="literal">stderr</code>.
      If the exception is derived from
      <code class="classname">std::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 <code class="function">std::abort</code>.
    </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("argc is greater than 5!");
   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 is printed by the shell after the process exits
      by calling <code class="function">abort()</code>.
    </p><p>
      As 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">&lt;exception&gt;</code> and
      <code class="filename">&lt;cstdlib&gt;</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
      <code class="literal">stderr</code>.  If your application closes
      <code class="literal">stderr</code> 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 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.
   Diagnostics

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	<!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 Stylesheets Vsnapshot" /><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.
	Support

	</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>
	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" type="1"><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 ();
	extern "C or C++" void f2 ();

	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"><div class="titlepage"><div><div><h3 class="title"><a id="support.termination.verbose"></a>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><p>
	The verbose terminate handler is only available for hosted environments
	(see <a class="xref" href="configure.html" title="Configure">Configuring</a>) and will be used
	by default unless the library is built with
	<code class="option">--disable-libstdcxx-verbose</code>
	or with exceptions disabled.
	If you need to enable it explicitly you can do so by calling the
	<code class="function">std::set_terminate</code> function.
	</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 <code class="literal">stderr</code>.
	If the exception is derived from
	<code class="classname">std::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 <code class="function">std::abort</code>.
	</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("argc is greater than 5!");
	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 is printed by the shell after the process exits
	by calling <code class="function">abort()</code>.
	</p><p>
	As 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
	<code class="literal">stderr</code>. If your application closes
	<code class="literal">stderr</code> 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 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.
	Diagnostics

	</td></tr></table></div></body></html>