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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>Chapter 27. Demangling</title><meta name="generator" content="DocBook XSL-NS Stylesheets V1.76.1"/><meta name="keywords" content="&#10;      ISO C++&#10;    , &#10;      library&#10;    "/><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. 
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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 27. Demangling"><div class="titlepage"><div><div><h2 class="title"><a id="manual.ext.demangle"/>Chapter 27. 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 &lt;exception&gt;
#include &lt;iostream&gt;
#include &lt;cxxabi.h&gt;

struct empty { };

template &lt;typename T, int N&gt;
  struct bar { };


int main()
{
  int     status;
  char   *realname;

  // exception classes not in &lt;stdexcept&gt;, thrown by the implementation
  // instead of the user
  std::bad_exception  e;
  realname = abi::__cxa_demangle(e.what(), 0, 0, &amp;status);
  std::cout &lt;&lt; e.what() &lt;&lt; "\t=&gt; " &lt;&lt; realname &lt;&lt; "\t: " &lt;&lt; status &lt;&lt; '\n';
  free(realname);


  // typeid
  bar&lt;empty,17&gt;          u;
  const std::type_info  &amp;ti = typeid(u);

  realname = abi::__cxa_demangle(ti.name(), 0, 0, &amp;status);
  std::cout &lt;&lt; ti.name() &lt;&lt; "\t=&gt; " &lt;&lt; realname &lt;&lt; "\t: " &lt;&lt; status &lt;&lt; '\n';
  free(realname);

  return 0;
}
   </pre><p>
     This prints
   </p><pre class="screen">
   <code class="computeroutput">
      St13bad_exception       =&gt; std::bad_exception   : 0
      3barI5emptyLi17EE       =&gt; bar&lt;empty, 17&gt;       : 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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