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"> 3<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Chapter 40. Demangling</title><meta name="generator" content="DocBook XSL Stylesheets V1.75.2" /><meta name="keywords" content=" ISO C++ , library " /><link rel="home" href="../spine.html" title="The GNU C++ Library Documentation" /><link rel="up" href="extensions.html" title="Part XII. Extensions" /><link rel="prev" href="ext_io.html" title="Chapter 39. Input and Output" /><link rel="next" href="ext_concurrency.html" title="Chapter 41. Concurrency" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 40. Demangling</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ext_io.html">Prev</a> </td><th width="60%" align="center">Part XII. 4 Extensions 5 6</th><td width="20%" align="right"> <a accesskey="n" href="ext_concurrency.html">Next</a></td></tr></table><hr /></div><div class="chapter" title="Chapter 40. Demangling"><div class="titlepage"><div><div><h2 class="title"><a id="manual.ext.demangle"></a>Chapter 40. Demangling</h2></div></div></div><p> 7 Transforming C++ ABI identifiers (like RTTI symbols) into the 8 original C++ source identifiers is called 9 <span class="quote">“<span class="quote">demangling.</span>”</span> 10 </p><p> 11 If you have read the <a class="ulink" href="http://gcc.gnu.org/onlinedocs/libstdc++/latest-doxygen/a01115.html" target="_top">source 12 documentation for <code class="code">namespace abi</code></a> then you are 13 aware of the cross-vendor C++ ABI in use by GCC. One of the 14 exposed functions is used for demangling, 15 <code class="code">abi::__cxa_demangle</code>. 16 </p><p> 17 In programs like <span class="command"><strong>c++filt</strong></span>, the linker, and other tools 18 have the ability to decode C++ ABI names, and now so can you. 19 </p><p> 20 (The function itself might use different demanglers, but that's the 21 whole point of abstract interfaces. If we change the implementation, 22 you won't notice.) 23 </p><p> 24 Probably the only times you'll be interested in demangling at runtime 25 are when you're seeing <code class="code">typeid</code> strings in RTTI, or when 26 you're handling the runtime-support exception classes. For example: 27 </p><pre class="programlisting"> 28#include <exception> 29#include <iostream> 30#include <cxxabi.h> 31 32struct empty { }; 33 34template <typename T, int N> 35 struct bar { }; 36 37 38int main() 39{ 40 int status; 41 char *realname; 42 43 // exception classes not in <stdexcept>, thrown by the implementation 44 // instead of the user 45 std::bad_exception e; 46 realname = abi::__cxa_demangle(e.what(), 0, 0, &status); 47 std::cout << e.what() << "\t=> " << realname << "\t: " << status << '\n'; 48 free(realname); 49 50 51 // typeid 52 bar<empty,17> u; 53 const std::type_info &ti = typeid(u); 54 55 realname = abi::__cxa_demangle(ti.name(), 0, 0, &status); 56 std::cout << ti.name() << "\t=> " << realname << "\t: " << status << '\n'; 57 free(realname); 58 59 return 0; 60} 61 </pre><p> 62 This prints 63 </p><pre class="screen"> 64 <code class="computeroutput"> 65 St13bad_exception => std::bad_exception : 0 66 3barI5emptyLi17EE => bar<empty, 17> : 0 67 </code> 68 </pre><p> 69 The demangler interface is described in the source documentation 70 linked to above. It is actually written in C, so you don't need to 71 be writing C++ in order to demangle C++. (That also means we have to 72 use crummy memory management facilities, so don't forget to free() 73 the returned char array.) 74 </p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ext_io.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="extensions.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="ext_concurrency.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 39. Input and Output </td><td width="20%" align="center"><a accesskey="h" href="../spine.html">Home</a></td><td width="40%" align="right" valign="top"> Chapter 41. Concurrency</td></tr></table></div></body></html> 75