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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.
Extensions
</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>
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/a01115.html">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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