1 <?xml version="1.0" encoding="UTF-8" standalone="no"?> 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 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="Chapter4. Support" /><link rel="prev" href="dynamic_memory.html" title="Dynamic Memory" /><link rel="next" href="diagnostics.html" title="Chapter5. 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">Chapter4. 3 Support 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 7 <code class="filename"><cstdlib></code>. 8 You should note that the 9 <code class="function">abort()</code> function does not call the 10 destructors of automatic nor static objects, so if you're 11 depending on those to do cleanup, it isn't going to happen. 12 (The functions registered with <code class="function">atexit()</code> 13 don't get called either, so you can forget about that 14 possibility, too.) 15 </p><p> 16 The good old <code class="function">exit()</code> function can be a bit 17 funky, too, until you look closer. Basically, three points to 18 remember are: 19 </p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p> 20 Static objects are destroyed in reverse order of their creation. 21 </p></li><li class="listitem"><p> 22 Functions registered with <code class="function">atexit()</code> are called in 23 reverse order of registration, once per registration call. 24 (This isn't actually new.) 25 </p></li><li class="listitem"><p> 26 The previous two actions are <span class="quote"><span class="quote">interleaved,</span></span> that is, 27 given this pseudocode: 28 </p><pre class="programlisting"> 29 extern "C or C++" void f1 (); 30 extern "C or C++" void f2 (); 31 32 static Thing obj1; 33 atexit(f1); 34 static Thing obj2; 35 atexit(f2); 36 </pre><p> 37 then at a call of <code class="function">exit()</code>, 38 <code class="varname">f2</code> will be called, then 39 <code class="varname">obj2</code> will be destroyed, then 40 <code class="varname">f1</code> will be called, and finally 41 <code class="varname">obj1</code> will be destroyed. If 42 <code class="varname">f1</code> or <code class="varname">f2</code> allow an 43 exception to propagate out of them, Bad Things happen. 44 </p></li></ol></div><p> 45 Note also that <code class="function">atexit()</code> is only required to store 32 46 functions, and the compiler/library might already be using some of 47 those slots. If you think you may run out, we recommend using 48 the <code class="function">xatexit</code>/<code class="function">xexit</code> combination 49 from <code class="literal">libiberty</code>, which has no such limit. 50 </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> 51 If you are having difficulty with uncaught exceptions and want a 52 little bit of help debugging the causes of the core dumps, you can 53 make use of a GNU extension, the verbose terminate handler. 54 </p><p> 55 The verbose terminate handler is only available for hosted environments 56 (see <a class="xref" href="configure.html" title="Configure">Configuring</a>) and will be used 57 by default unless the library is built with 58 <code class="option">--disable-libstdcxx-verbose</code> 59 or with exceptions disabled. 60 If you need to enable it explicitly you can do so by calling the 61 <code class="function">std::set_terminate</code> function. 62 </p><pre class="programlisting"> 63 #include <exception> 64 65 int main() 66 { 67 std::set_terminate(__gnu_cxx::__verbose_terminate_handler); 68 ... 69 70 throw <em class="replaceable"><code>anything</code></em>; 71 } 72 </pre><p> 73 The <code class="function">__verbose_terminate_handler</code> function 74 obtains the name of the current exception, attempts to demangle 75 it, and prints it to <code class="literal">stderr</code>. 76 If the exception is derived from 77 <code class="classname">std::exception</code> then the output from 78 <code class="function">what()</code> will be included. 79 </p><p> 80 Any replacement termination function is required to kill the 81 program without returning; this one calls <code class="function">std::abort</code>. 82 </p><p> 83 For example: 84 </p><pre class="programlisting"> 85 #include <exception> 86 #include <stdexcept> 87 88 struct argument_error : public std::runtime_error 89 { 90 argument_error(const std::string& s): std::runtime_error(s) { } 91 }; 92 93 int main(int argc) 94 { 95 std::set_terminate(__gnu_cxx::__verbose_terminate_handler); 96 if (argc > 5) 97 throw argument_error("argc is greater than 5!"); 98 else 99 throw argc; 100 } 101 </pre><p> 102 With the verbose terminate handler active, this gives: 103 </p><pre class="screen"> 104 <code class="computeroutput"> 105 % ./a.out 106 terminate called after throwing a `int' 107 Aborted 108 % ./a.out f f f f f f f f f f f 109 terminate called after throwing an instance of `argument_error' 110 what(): argc is greater than 5! 111 Aborted 112 </code> 113 </pre><p> 114 The 'Aborted' line is printed by the shell after the process exits 115 by calling <code class="function">abort()</code>. 116 </p><p> 117 As this is the default termination handler, nothing need be done to 118 use it. To go back to the previous <span class="quote"><span class="quote">silent death</span></span> 119 method, simply include 120 <code class="filename"><exception></code> and 121 <code class="filename"><cstdlib></code>, and call 122 </p><pre class="programlisting"> 123 std::set_terminate(std::abort); 124 </pre><p> 125 After this, all calls to <code class="function">terminate</code> will use 126 <code class="function">abort</code> as the terminate handler. 127 </p><p> 128 Note: the verbose terminate handler will attempt to write to 129 <code class="literal">stderr</code>. If your application closes 130 <code class="literal">stderr</code> or redirects it to an inappropriate location, 131 <code class="function">__verbose_terminate_handler</code> will behave in 132 an unspecified manner. 133 </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">Chapter5. 134 Diagnostics 135 136 </td></tr></table></div></body></html>
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