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Extensions
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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="https://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 time you'll be interested in demangling at runtime
is when you're seeing <code class="code">typeid</code> strings in RTTI. For example:
</p><pre class="programlisting">
#include <iostream>
#include <cstdlib>
#include <cxxabi.h>
struct empty { };
template <typename T, int N>
struct bar { };
int main()
{
int status;
char *realname;
// typeid
bar<empty,17> u;
const std::type_info &ti = typeid(u);
realname = abi::__cxa_demangle(ti.name(), NULL, NULL, &status);
std::cout << ti.name() << "\t=> " << realname << "\t: " << status << '\n';
std::free(realname);
}
</pre><p>
This prints
</p><pre class="screen">
<code class="computeroutput">
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
<code class="code">free()</code> the returned char array.)
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