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jeremybenn |
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>Chapter 29. Demangling</title><meta name="generator" content="DocBook XSL-NS Stylesheets V1.76.1"/><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 28. Input and Output"/><link rel="next" href="ext_concurrency.html" title="Chapter 30. Concurrency"/></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 29. Demangling</th></tr><tr><td align="left"><a accesskey="p" href="ext_io.html">Prev</a> </td><th width="60%" align="center">Part III.
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Extensions
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</th><td align="right"> <a accesskey="n" href="ext_concurrency.html">Next</a></td></tr></table><hr/></div><div class="chapter" title="Chapter 29. Demangling"><div class="titlepage"><div><div><h2 class="title"><a id="manual.ext.demangle"/>Chapter 29. Demangling</h2></div></div></div><p>
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Transforming C++ ABI identifiers (like RTTI symbols) into the
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original C++ source identifiers is called
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<span class="quote">“<span class="quote">demangling.</span>”</span>
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</p><p>
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If you have read the <a class="link" href="http://gcc.gnu.org/onlinedocs/libstdc++/latest-doxygen/a01115.html">source
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documentation for <code class="code">namespace abi</code></a> then you are
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aware of the cross-vendor C++ ABI in use by GCC. One of the
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exposed functions is used for demangling,
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<code class="code">abi::__cxa_demangle</code>.
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</p><p>
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In programs like <span class="command"><strong>c++filt</strong></span>, the linker, and other tools
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have the ability to decode C++ ABI names, and now so can you.
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</p><p>
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(The function itself might use different demanglers, but that's the
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whole point of abstract interfaces. If we change the implementation,
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you won't notice.)
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</p><p>
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Probably the only times you'll be interested in demangling at runtime
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are when you're seeing <code class="code">typeid</code> strings in RTTI, or when
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you're handling the runtime-support exception classes. For example:
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</p><pre class="programlisting">
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#include <exception>
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#include <iostream>
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#include <cxxabi.h>
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struct empty { };
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template <typename T, int N>
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struct bar { };
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int main()
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{
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int status;
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char *realname;
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// exception classes not in <stdexcept>, thrown by the implementation
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// instead of the user
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std::bad_exception e;
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realname = abi::__cxa_demangle(e.what(), 0, 0, &status);
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std::cout << e.what() << "\t=> " << realname << "\t: " << status << '\n';
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free(realname);
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// typeid
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bar<empty,17> u;
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const std::type_info &ti = typeid(u);
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realname = abi::__cxa_demangle(ti.name(), 0, 0, &status);
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std::cout << ti.name() << "\t=> " << realname << "\t: " << status << '\n';
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free(realname);
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return 0;
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}
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</pre><p>
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This prints
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</p><pre class="screen">
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<code class="computeroutput">
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St13bad_exception => std::bad_exception : 0
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3barI5emptyLi17EE => bar<empty, 17> : 0
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</code>
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</pre><p>
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The demangler interface is described in the source documentation
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linked to above. It is actually written in C, so you don't need to
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be writing C++ in order to demangle C++. (That also means we have to
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use crummy memory management facilities, so don't forget to free()
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the returned char array.)
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</p></div><div class="navfooter"><hr/><table width="100%" summary="Navigation footer"><tr><td align="left"><a accesskey="p" href="ext_io.html">Prev</a> </td><td align="center"><a accesskey="u" href="extensions.html">Up</a></td><td align="right"> <a accesskey="n" href="ext_concurrency.html">Next</a></td></tr><tr><td align="left" valign="top">Chapter 28. Input and Output </td><td align="center"><a accesskey="h" href="../index.html">Home</a></td><td align="right" valign="top"> Chapter 30. Concurrency</td></tr></table></div></body></html>
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