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3 <html xmlns="http://www.w3.org/1999/xhtml"><head><title>Chapter 27. Demangling</title><meta name="generator" content="DocBook XSL-NS Stylesheets V1.75.2"/><meta name="keywords" content=" ISO C++ , library "/><link rel="home" href="../spine.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 26. Input and Output"/><link rel="next" href="ext_concurrency.html" title="Chapter 28. Concurrency"/></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 27. Demangling</th></tr><tr><td align="left"><a accesskey="p" href="ext_io.html">Prev</a> </td><th width="60%" align="center">Part III.
6 </th><td align="right"> <a accesskey="n" href="ext_concurrency.html">Next</a></td></tr></table><hr/></div><div class="chapter" title="Chapter 27. Demangling"><div class="titlepage"><div><div><h1 class="title"><a id="manual.ext.demangle"/>Demangling</h1></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>
11 If you have read the <a class="link" href="http://gcc.gnu.org/onlinedocs/libstdc++/latest-doxygen/a01115.html" target="">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>.
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.
20 (The function itself might use different demanglers, but that's the
21 whole point of abstract interfaces. If we change the implementation,
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>
34 template <typename T, int N>
43 // exception classes not in <stdexcept>, thrown by the implementation
44 // instead of the user
46 realname = abi::__cxa_demangle(e.what(), 0, 0, &status);
47 std::cout << e.what() << "\t=> " << realname << "\t: " << status << '\n';
52 bar<empty,17> u;
53 const std::type_info &ti = typeid(u);
55 realname = abi::__cxa_demangle(ti.name(), 0, 0, &status);
56 std::cout << ti.name() << "\t=> " << realname << "\t: " << status << '\n';
63 </p><pre class="screen">
64 <code class="computeroutput">
65 St13bad_exception => std::bad_exception : 0
66 3barI5emptyLi17EE => bar<empty, 17> : 0
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.)
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