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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>Chapter 28. Demangling</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="extensions.html" title="Part III. Extensions" /><link rel="prev" href="ext_io.html" title="Chapter 27. Input and Output" /><link rel="next" href="ext_concurrency.html" title="Chapter 29. Concurrency" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 28. 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 III. |
| Extensions |
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| </th><td width="20%" align="right"> <a accesskey="n" href="ext_concurrency.html">Next</a></td></tr></table><hr /></div><div class="chapter"><div class="titlepage"><div><div><h2 class="title"><a id="manual.ext.demangle"></a>Chapter 28. Demangling</h2></div></div></div><p> |
| Transforming C++ ABI identifiers (like RTTI symbols) into the |
| original C++ source identifiers is called |
| <span class="quote">“<span class="quote">demangling.</span>”</span> |
| </p><p> |
| If you have read the <a class="link" href="http://gcc.gnu.org/onlinedocs/libstdc++/latest-doxygen/namespaces.html" target="_top">source |
| documentation for <code class="code">namespace abi</code></a> then you are |
| aware of the cross-vendor C++ ABI in use by GCC. One of the |
| exposed functions is used for demangling, |
| <code class="code">abi::__cxa_demangle</code>. |
| </p><p> |
| In programs like <span class="command"><strong>c++filt</strong></span>, the linker, and other tools |
| have the ability to decode C++ ABI names, and now so can you. |
| </p><p> |
| (The function itself might use different demanglers, but that's the |
| whole point of abstract interfaces. If we change the implementation, |
| you won't notice.) |
| </p><p> |
| Probably the only times you'll be interested in demangling at runtime |
| are when you're seeing <code class="code">typeid</code> strings in RTTI, or when |
| you're handling the runtime-support exception classes. For example: |
| </p><pre class="programlisting"> |
| #include <exception> |
| #include <iostream> |
| #include <cxxabi.h> |
| |
| struct empty { }; |
| |
| template <typename T, int N> |
| struct bar { }; |
| |
| |
| int main() |
| { |
| int status; |
| char *realname; |
| |
| // exception classes not in <stdexcept>, thrown by the implementation |
| // instead of the user |
| std::bad_exception e; |
| realname = abi::__cxa_demangle(e.what(), 0, 0, &status); |
| std::cout << e.what() << "\t=> " << realname << "\t: " << status << '\n'; |
| free(realname); |
| |
| |
| // typeid |
| bar<empty,17> u; |
| const std::type_info &ti = typeid(u); |
| |
| realname = abi::__cxa_demangle(ti.name(), 0, 0, &status); |
| std::cout << ti.name() << "\t=> " << realname << "\t: " << status << '\n'; |
| free(realname); |
| |
| return 0; |
| } |
| </pre><p> |
| This prints |
| </p><pre class="screen"> |
| <code class="computeroutput"> |
| St13bad_exception => std::bad_exception : 0 |
| 3barI5emptyLi17EE => bar<empty, 17> : 0 |
| </code> |
| </pre><p> |
| The demangler interface is described in the source documentation |
| linked to above. It is actually written in C, so you don't need to |
| be writing C++ in order to demangle C++. (That also means we have to |
| use crummy memory management facilities, so don't forget to free() |
| the returned char array.) |
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