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198 lines
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<html lang="en">
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<title>c++filt - GNU Binary Utilities</title>
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Permission is granted to copy, distribute and/or modify this document
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</head>
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<div class="node">
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<a name="c++filt"></a>
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<a name="c_002b_002bfilt"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="addr2line.html#addr2line">addr2line</a>,
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Previous: <a rel="previous" accesskey="p" href="strip.html#strip">strip</a>,
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Up: <a rel="up" accesskey="u" href="index.html#Top">Top</a>
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<hr>
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</div>
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<h2 class="chapter">9 c++filt</h2>
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<p><a name="index-c_002b_002bfilt-141"></a><a name="index-demangling-C_002b_002b-symbols-142"></a>
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<!-- man title cxxfilt demangle C++ and Java symbols -->
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<pre class="smallexample"> <!-- man begin SYNOPSIS cxxfilt -->
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c++filt [<samp><span class="option">-_</span></samp>|<samp><span class="option">--strip-underscore</span></samp>]
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[<samp><span class="option">-n</span></samp>|<samp><span class="option">--no-strip-underscore</span></samp>]
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[<samp><span class="option">-p</span></samp>|<samp><span class="option">--no-params</span></samp>]
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[<samp><span class="option">-t</span></samp>|<samp><span class="option">--types</span></samp>]
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[<samp><span class="option">-i</span></samp>|<samp><span class="option">--no-verbose</span></samp>]
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[<samp><span class="option">-r</span></samp>|<samp><span class="option">--no-recurse-limit</span></samp>]
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[<samp><span class="option">-R</span></samp>|<samp><span class="option">--recurse-limit</span></samp>]
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[<samp><span class="option">-s</span></samp> <var>format</var>|<samp><span class="option">--format=</span></samp><var>format</var>]
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[<samp><span class="option">--help</span></samp>] [<samp><span class="option">--version</span></samp>] [<var>symbol</var>...]
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<!-- man end -->
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</pre>
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<!-- man begin DESCRIPTION cxxfilt -->
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<p><a name="index-cxxfilt-143"></a>The C++ and Java languages provide function overloading, which means
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that you can write many functions with the same name, providing that
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each function takes parameters of different types. In order to be
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able to distinguish these similarly named functions C++ and Java
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encode them into a low-level assembler name which uniquely identifies
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each different version. This process is known as <dfn>mangling</dfn>. The
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<samp><span class="command">c++filt</span></samp>
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<a rel="footnote" href="#fn-1" name="fnd-1"><sup>1</sup></a>
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program does the inverse mapping: it decodes (<dfn>demangles</dfn>) low-level
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names into user-level names so that they can be read.
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<p>Every alphanumeric word (consisting of letters, digits, underscores,
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dollars, or periods) seen in the input is a potential mangled name.
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If the name decodes into a C++ name, the C++ name replaces the
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low-level name in the output, otherwise the original word is output.
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In this way you can pass an entire assembler source file, containing
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mangled names, through <samp><span class="command">c++filt</span></samp> and see the same source file
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containing demangled names.
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<p>You can also use <samp><span class="command">c++filt</span></samp> to decipher individual symbols by
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passing them on the command line:
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<pre class="example"> c++filt <var>symbol</var>
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</pre>
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<p>If no <var>symbol</var> arguments are given, <samp><span class="command">c++filt</span></samp> reads symbol
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names from the standard input instead. All the results are printed on
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the standard output. The difference between reading names from the
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command line versus reading names from the standard input is that
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command-line arguments are expected to be just mangled names and no
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checking is performed to separate them from surrounding text. Thus
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for example:
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<pre class="smallexample"> c++filt -n _Z1fv
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</pre>
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<p>will work and demangle the name to “f()” whereas:
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<pre class="smallexample"> c++filt -n _Z1fv,
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</pre>
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<p>will not work. (Note the extra comma at the end of the mangled
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name which makes it invalid). This command however will work:
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<pre class="smallexample"> echo _Z1fv, | c++filt -n
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</pre>
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<p>and will display “f(),”, i.e., the demangled name followed by a
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trailing comma. This behaviour is because when the names are read
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from the standard input it is expected that they might be part of an
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assembler source file where there might be extra, extraneous
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characters trailing after a mangled name. For example:
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<pre class="smallexample"> .type _Z1fv, @function
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</pre>
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<!-- man end -->
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<!-- man begin OPTIONS cxxfilt -->
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<dl>
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<dt><samp><span class="env">-_</span></samp><dt><samp><span class="env">--strip-underscore</span></samp><dd>On some systems, both the C and C++ compilers put an underscore in front
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of every name. For example, the C name <code>foo</code> gets the low-level
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name <code>_foo</code>. This option removes the initial underscore. Whether
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<samp><span class="command">c++filt</span></samp> removes the underscore by default is target dependent.
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<br><dt><samp><span class="env">-n</span></samp><dt><samp><span class="env">--no-strip-underscore</span></samp><dd>Do not remove the initial underscore.
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<br><dt><samp><span class="env">-p</span></samp><dt><samp><span class="env">--no-params</span></samp><dd>When demangling the name of a function, do not display the types of
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the function's parameters.
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<br><dt><samp><span class="env">-t</span></samp><dt><samp><span class="env">--types</span></samp><dd>Attempt to demangle types as well as function names. This is disabled
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by default since mangled types are normally only used internally in
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the compiler, and they can be confused with non-mangled names. For example,
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a function called “a” treated as a mangled type name would be
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demangled to “signed char”.
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<br><dt><samp><span class="env">-i</span></samp><dt><samp><span class="env">--no-verbose</span></samp><dd>Do not include implementation details (if any) in the demangled
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output.
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<br><dt><samp><span class="env">-r</span></samp><dt><samp><span class="env">-R</span></samp><dt><samp><span class="env">--recurse-limit</span></samp><dt><samp><span class="env">--no-recurse-limit</span></samp><dt><samp><span class="env">--recursion-limit</span></samp><dt><samp><span class="env">--no-recursion-limit</span></samp><dd>Enables or disables a limit on the amount of recursion performed
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whilst demangling strings. Since the name mangling formats allow for
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an inifinite level of recursion it is possible to create strings whose
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decoding will exhaust the amount of stack space available on the host
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machine, triggering a memory fault. The limit tries to prevent this
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from happening by restricting recursion to 2048 levels of nesting.
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<p>The default is for this limit to be enabled, but disabling it may be
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necessary in order to demangle truly complicated names. Note however
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that if the recursion limit is disabled then stack exhaustion is
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possible and any bug reports about such an event will be rejected.
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<p>The <samp><span class="option">-r</span></samp> option is a synonym for the
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<samp><span class="option">--no-recurse-limit</span></samp> option. The <samp><span class="option">-R</span></samp> option is a
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synonym for the <samp><span class="option">--recurse-limit</span></samp> option.
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<br><dt><samp><span class="env">-s </span><var>format</var></samp><dt><samp><span class="env">--format=</span><var>format</var></samp><dd><samp><span class="command">c++filt</span></samp> can decode various methods of mangling, used by
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different compilers. The argument to this option selects which
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method it uses:
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<dl>
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<dt><code>auto</code><dd>Automatic selection based on executable (the default method)
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<br><dt><code>gnu</code><dd>the one used by the <span class="sc">gnu</span> C++ compiler (g++)
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<br><dt><code>lucid</code><dd>the one used by the Lucid compiler (lcc)
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<br><dt><code>arm</code><dd>the one specified by the C++ Annotated Reference Manual
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<br><dt><code>hp</code><dd>the one used by the HP compiler (aCC)
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<br><dt><code>edg</code><dd>the one used by the EDG compiler
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<br><dt><code>gnu-v3</code><dd>the one used by the <span class="sc">gnu</span> C++ compiler (g++) with the V3 ABI.
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<br><dt><code>java</code><dd>the one used by the <span class="sc">gnu</span> Java compiler (gcj)
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<br><dt><code>gnat</code><dd>the one used by the <span class="sc">gnu</span> Ada compiler (GNAT).
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</dl>
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<br><dt><samp><span class="env">--help</span></samp><dd>Print a summary of the options to <samp><span class="command">c++filt</span></samp> and exit.
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<br><dt><samp><span class="env">--version</span></samp><dd>Print the version number of <samp><span class="command">c++filt</span></samp> and exit.
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</dl>
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<!-- man end -->
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<blockquote>
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<em>Warning:</em> <samp><span class="command">c++filt</span></samp> is a new utility, and the details of its
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user interface are subject to change in future releases. In particular,
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a command-line option may be required in the future to decode a name
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passed as an argument on the command line; in other words,
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<pre class="example"> c++filt <var>symbol</var>
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</pre>
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<p class="noindent">may in a future release become
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<pre class="example"> c++filt <var>option</var> <var>symbol</var>
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</pre>
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</blockquote>
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<div class="footnote">
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<hr>
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<h4>Footnotes</h4><p class="footnote"><small>[<a name="fn-1" href="#fnd-1">1</a>]</small> MS-DOS does not allow <kbd>+</kbd> characters in file names, so on
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MS-DOS this program is named <samp><span class="command">CXXFILT</span></samp>.</p>
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<hr></div>
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