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|  | <TITLE>G++ internals - Mangling</TITLE> | 
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|  | <H2><A NAME="SEC20" HREF="gxxint_toc.html#TOC20">Function name mangling for C++ and Java</A></H2> | 
|  |  | 
|  | <P> | 
|  | Both C++ and Jave provide overloaded function and methods, | 
|  | which are methods with the same types but different parameter lists. | 
|  | Selecting the correct version is done at compile time. | 
|  | Though the overloaded functions have the same name in the source code, | 
|  | they need to be translated into different assembler-level names, | 
|  | since typical assemblers and linkers cannot handle overloading. | 
|  | This process of encoding the parameter types with the method name | 
|  | into a unique name is called <EM>name mangling</EM>.  The inverse | 
|  | process is called <EM>demangling</EM>. | 
|  |  | 
|  | </P> | 
|  | <P> | 
|  | It is convenient that C++ and Java use compatible mangling schemes, | 
|  | since the makes life easier for tools such as gdb, and it eases | 
|  | integration between C++ and Java. | 
|  |  | 
|  | </P> | 
|  | <P> | 
|  | Note there is also a standard "Jave Native Interface" (JNI) which | 
|  | implements a different calling convention, and uses a different | 
|  | mangling scheme.  The JNI is a rather abstract ABI so Java can call methods | 
|  | written in C or C++; | 
|  | we are concerned here about a lower-level interface primarily | 
|  | intended for methods written in Java, but that can also be used for C++ | 
|  | (and less easily C). | 
|  |  | 
|  | </P> | 
|  |  | 
|  |  | 
|  | <H3><A NAME="SEC21" HREF="gxxint_toc.html#TOC21">Method name mangling</A></H3> | 
|  |  | 
|  | <P> | 
|  | C++ mangles a method by emitting the function name, followed by <CODE>__</CODE>, | 
|  | followed by encodings of any method qualifiers (such as <CODE>const</CODE>), | 
|  | followed by the mangling of the method's class, | 
|  | followed by the mangling of the parameters, in order. | 
|  |  | 
|  | </P> | 
|  | <P> | 
|  | For example <CODE>Foo::bar(int, long) const</CODE> is mangled | 
|  | as <SAMP>`bar__C3Fooil'</SAMP>. | 
|  |  | 
|  | </P> | 
|  | <P> | 
|  | For a constructor, the method name is left out. | 
|  | That is <CODE>Foo::Foo(int, long) const</CODE>  is mangled | 
|  | as <SAMP>`__C3Fooil'</SAMP>. | 
|  |  | 
|  | </P> | 
|  | <P> | 
|  | GNU Java does the same. | 
|  |  | 
|  | </P> | 
|  |  | 
|  |  | 
|  | <H3><A NAME="SEC22" HREF="gxxint_toc.html#TOC22">Primitive types</A></H3> | 
|  |  | 
|  | <P> | 
|  | The C++ types <CODE>int</CODE>, <CODE>long</CODE>, <CODE>short</CODE>, <CODE>char</CODE>, | 
|  | and <CODE>long long</CODE> are mangled as <SAMP>`i'</SAMP>, <SAMP>`l'</SAMP>, | 
|  | <SAMP>`s'</SAMP>, <SAMP>`c'</SAMP>, and <SAMP>`x'</SAMP>, respectively. | 
|  | The corresponding unsigned types have <SAMP>`U'</SAMP> prefixed | 
|  | to the mangling.  The type <CODE>signed char</CODE> is mangled <SAMP>`Sc'</SAMP>. | 
|  |  | 
|  | </P> | 
|  | <P> | 
|  | The C++ and Java floating-point types <CODE>float</CODE> and <CODE>double</CODE> | 
|  | are mangled as <SAMP>`f'</SAMP> and <SAMP>`d'</SAMP> respectively. | 
|  |  | 
|  | </P> | 
|  | <P> | 
|  | The C++ <CODE>bool</CODE> type and the Java <CODE>boolean</CODE> type are | 
|  | mangled as <SAMP>`b'</SAMP>. | 
|  |  | 
|  | </P> | 
|  | <P> | 
|  | The C++ <CODE>wchar_t</CODE> and the Java <CODE>char</CODE> types are | 
|  | mangled as <SAMP>`w'</SAMP>. | 
|  |  | 
|  | </P> | 
|  | <P> | 
|  | The Java integral types <CODE>byte</CODE>, <CODE>short</CODE>, <CODE>int</CODE> | 
|  | and <CODE>long</CODE> are mangled as <SAMP>`c'</SAMP>, <SAMP>`s'</SAMP>, <SAMP>`i'</SAMP>, | 
|  | and <SAMP>`x'</SAMP>, respectively. | 
|  |  | 
|  | </P> | 
|  | <P> | 
|  | C++ code that has included <CODE>javatypes.h</CODE> will mangle | 
|  | the typedefs  <CODE>jbyte</CODE>, <CODE>jshort</CODE>, <CODE>jint</CODE> | 
|  | and <CODE>jlong</CODE> as respectively <SAMP>`c'</SAMP>, <SAMP>`s'</SAMP>, <SAMP>`i'</SAMP>, | 
|  | and <SAMP>`x'</SAMP>.  (This has not been implemented yet.) | 
|  |  | 
|  | </P> | 
|  |  | 
|  |  | 
|  | <H3><A NAME="SEC23" HREF="gxxint_toc.html#TOC23">Mangling of simple names</A></H3> | 
|  |  | 
|  | <P> | 
|  | A simple class, package, template, or namespace name is | 
|  | encoded as the number of characters in the name, followed by | 
|  | the actual characters.  Thus the class <CODE>Foo</CODE> | 
|  | is encoded as <SAMP>`3Foo'</SAMP>. | 
|  |  | 
|  | </P> | 
|  | <P> | 
|  | If any of the characters in the name are not alphanumeric | 
|  | (i.e not one of the standard ASCII letters, digits, or '_'), | 
|  | or the initial character is a digit, then the name is | 
|  | mangled as a sequence of encoded Unicode letters. | 
|  | A Unicode encoding starts with a <SAMP>`U'</SAMP> to indicate | 
|  | that Unicode escapes are used, followed by the number of | 
|  | bytes used by the Unicode encoding, followed by the bytes | 
|  | representing the encoding.  ASSCI letters and | 
|  | non-initial digits are encoded without change.  However, all | 
|  | other characters (including underscore and initial digits) are | 
|  | translated into a sequence starting with an underscore, | 
|  | followed by the big-endian 4-hex-digit lower-case encoding of the character. | 
|  |  | 
|  | </P> | 
|  | <P> | 
|  | If a method name contains Unicode-escaped characters, the | 
|  | entire mangled method name is followed by a <SAMP>`U'</SAMP>. | 
|  |  | 
|  | </P> | 
|  | <P> | 
|  | For example, the method <CODE>X\u0319::M\u002B(int)</CODE> is encoded as | 
|  | <SAMP>`M_002b__U6X_0319iU'</SAMP>. | 
|  |  | 
|  | </P> | 
|  |  | 
|  |  | 
|  | <H3><A NAME="SEC24" HREF="gxxint_toc.html#TOC24">Pointer and reference types</A></H3> | 
|  |  | 
|  | <P> | 
|  | A C++ pointer type is mangled as <SAMP>`P'</SAMP> followed by the | 
|  | mangling of the type pointed to. | 
|  |  | 
|  | </P> | 
|  | <P> | 
|  | A C++ reference type as mangled as <SAMP>`R'</SAMP> followed by the | 
|  | mangling of the type referenced. | 
|  |  | 
|  | </P> | 
|  | <P> | 
|  | A Java object reference type is equivalent | 
|  | to a C++ pointer parameter, so we mangle such an parameter type | 
|  | as <SAMP>`P'</SAMP> followed by the mangling of the class name. | 
|  |  | 
|  | </P> | 
|  |  | 
|  |  | 
|  | <H3><A NAME="SEC25" HREF="gxxint_toc.html#TOC25">Qualified names</A></H3> | 
|  |  | 
|  | <P> | 
|  | Both C++ and Java allow a class to be lexically nested inside another | 
|  | class.  C++ also supports namespaces (not yet implemented by G++). | 
|  | Java also supports packages. | 
|  |  | 
|  | </P> | 
|  | <P> | 
|  | These are all mangled the same way:  First the letter <SAMP>`Q'</SAMP> | 
|  | indicates that we are emitting a qualified name. | 
|  | That is followed by the number of parts in the qualified name. | 
|  | If that number is 9 or less, it is emitted with no delimiters. | 
|  | Otherwise, an underscore is written before and after the count. | 
|  | Then follows each part of the qualified name, as described above. | 
|  |  | 
|  | </P> | 
|  | <P> | 
|  | For example <CODE>Foo::\u0319::Bar</CODE> is encoded as | 
|  | <SAMP>`Q33FooU5_03193Bar'</SAMP>. | 
|  |  | 
|  | </P> | 
|  |  | 
|  |  | 
|  | <H3><A NAME="SEC26" HREF="gxxint_toc.html#TOC26">Templates</A></H3> | 
|  |  | 
|  | <P> | 
|  | A class template instantiation is encoded as the letter <SAMP>`t'</SAMP>, | 
|  | followed by the encoding of the template name, followed | 
|  | the number of template parameters, followed by encoding of the template | 
|  | parameters.  If a template parameter is a type, it is written | 
|  | as a <SAMP>`Z'</SAMP> followed by the encoding of the type. | 
|  |  | 
|  | </P> | 
|  | <P> | 
|  | A function template specialization (either an instantiation or an | 
|  | explicit specialization) is encoded by an <SAMP>`H'</SAMP> followed by the | 
|  | encoding of the template parameters, as described above, followed by | 
|  | an <SAMP>`_'</SAMP>, the encoding of the argument types template function (not the | 
|  | specialization), another <SAMP>`_'</SAMP>, and the return type.  (Like the | 
|  | argument types, the return type is the return type of the function | 
|  | template, not the specialization.)  Template parameters in the argument | 
|  | and return types are encoded by an <SAMP>`X'</SAMP> for type parameters, or a | 
|  | <SAMP>`Y'</SAMP> for constant parameters, and an index indicating their position | 
|  | in the template parameter list declaration. | 
|  |  | 
|  | </P> | 
|  |  | 
|  |  | 
|  | <H3><A NAME="SEC27" HREF="gxxint_toc.html#TOC27">Arrays</A></H3> | 
|  |  | 
|  | <P> | 
|  | C++ array types are mangled by emitting <SAMP>`A'</SAMP>, followed by | 
|  | the length of the array, followed by an <SAMP>`_'</SAMP>, followed by | 
|  | the mangling of the element type.  Of course, normally | 
|  | array parameter types decay into a pointer types, so you | 
|  | don't see this. | 
|  |  | 
|  | </P> | 
|  | <P> | 
|  | Java arrays are objects.  A Java type <CODE>T[]</CODE> is mangled | 
|  | as if it were the C++ type <CODE>JArray<T></CODE>. | 
|  | For example <CODE>java.lang.String[]</CODE> is encoded as | 
|  | <SAMP>`Pt6JArray1ZPQ34java4lang6String'</SAMP>. | 
|  |  | 
|  | </P> | 
|  |  | 
|  |  | 
|  | <H3><A NAME="SEC28" HREF="gxxint_toc.html#TOC28">Table of demangling code characters</A></H3> | 
|  |  | 
|  | <P> | 
|  | The following special characters are used in mangling: | 
|  |  | 
|  | </P> | 
|  | <DL COMPACT> | 
|  |  | 
|  | <DT><SAMP>`A'</SAMP> | 
|  | <DD> | 
|  | Indicates a C++ array type. | 
|  |  | 
|  | <DT><SAMP>`b'</SAMP> | 
|  | <DD> | 
|  | Encodes the C++ <CODE>bool</CODE> type, | 
|  | and the Java <CODE>boolean</CODE> type. | 
|  |  | 
|  | <DT><SAMP>`c'</SAMP> | 
|  | <DD> | 
|  | Encodes the C++ <CODE>char</CODE> type, and the Java <CODE>byte</CODE> type. | 
|  |  | 
|  | <DT><SAMP>`C'</SAMP> | 
|  | <DD> | 
|  | A modifier to indicate a <CODE>const</CODE> type. | 
|  | Also used to indicate a <CODE>const</CODE> member function | 
|  | (in which cases it precedes the encoding of the method's class). | 
|  |  | 
|  | <DT><SAMP>`d'</SAMP> | 
|  | <DD> | 
|  | Encodes the C++ and Java <CODE>double</CODE> types. | 
|  |  | 
|  | <DT><SAMP>`e'</SAMP> | 
|  | <DD> | 
|  | Indicates extra unknown arguments <CODE>...</CODE>. | 
|  |  | 
|  | <DT><SAMP>`f'</SAMP> | 
|  | <DD> | 
|  | Encodes the C++ and Java <CODE>float</CODE> types. | 
|  |  | 
|  | <DT><SAMP>`F'</SAMP> | 
|  | <DD> | 
|  | Used to indicate a function type. | 
|  |  | 
|  | <DT><SAMP>`H'</SAMP> | 
|  | <DD> | 
|  | Used to indicate a template function. | 
|  |  | 
|  | <DT><SAMP>`i'</SAMP> | 
|  | <DD> | 
|  | Encodes the C++ and Java <CODE>int</CODE> types. | 
|  |  | 
|  | <DT><SAMP>`J'</SAMP> | 
|  | <DD> | 
|  | Indicates a complex type. | 
|  |  | 
|  | <DT><SAMP>`l'</SAMP> | 
|  | <DD> | 
|  | Encodes the C++ <CODE>long</CODE> type. | 
|  |  | 
|  | <DT><SAMP>`P'</SAMP> | 
|  | <DD> | 
|  | Indicates a pointer type.  Followed by the type pointed to. | 
|  |  | 
|  | <DT><SAMP>`Q'</SAMP> | 
|  | <DD> | 
|  | Used to mangle qualified names, which arise from nested classes. | 
|  | Should also be used for namespaces (?). | 
|  | In Java used to mangle package-qualified names, and inner classes. | 
|  |  | 
|  | <DT><SAMP>`r'</SAMP> | 
|  | <DD> | 
|  | Encodes the GNU C++ <CODE>long double</CODE> type. | 
|  |  | 
|  | <DT><SAMP>`R'</SAMP> | 
|  | <DD> | 
|  | Indicates a reference type.  Followed by the referenced type. | 
|  |  | 
|  | <DT><SAMP>`s'</SAMP> | 
|  | <DD> | 
|  | Encodes the C++ and java <CODE>short</CODE> types. | 
|  |  | 
|  | <DT><SAMP>`S'</SAMP> | 
|  | <DD> | 
|  | A modifier that indicates that the following integer type is signed. | 
|  | Only used with <CODE>char</CODE>. | 
|  |  | 
|  | Also used as a modifier to indicate a static member function. | 
|  |  | 
|  | <DT><SAMP>`t'</SAMP> | 
|  | <DD> | 
|  | Indicates a template instantiation. | 
|  |  | 
|  | <DT><SAMP>`T'</SAMP> | 
|  | <DD> | 
|  | A back reference to a previously seen type. | 
|  |  | 
|  | <DT><SAMP>`U'</SAMP> | 
|  | <DD> | 
|  | A modifier that indicates that the following integer type is unsigned. | 
|  | Also used to indicate that the following class or namespace name | 
|  | is encoded using Unicode-mangling. | 
|  |  | 
|  | <DT><SAMP>`v'</SAMP> | 
|  | <DD> | 
|  | Encodes the C++ and Java <CODE>void</CODE> types. | 
|  |  | 
|  | <DT><SAMP>`V'</SAMP> | 
|  | <DD> | 
|  | A modified for a <CODE>const</CODE> type or method. | 
|  |  | 
|  | <DT><SAMP>`w'</SAMP> | 
|  | <DD> | 
|  | Encodes the C++ <CODE>wchar_t</CODE> type, and the Java <CODE>char</CODE> types. | 
|  |  | 
|  | <DT><SAMP>`x'</SAMP> | 
|  | <DD> | 
|  | Encodes the GNU C++ <CODE>long long</CODE> type, and the Java <CODE>long</CODE> type. | 
|  |  | 
|  | <DT><SAMP>`X'</SAMP> | 
|  | <DD> | 
|  | Encodes a template type parameter, when part of a function type. | 
|  |  | 
|  | <DT><SAMP>`Y'</SAMP> | 
|  | <DD> | 
|  | Encodes a template constant parameter, when part of a function type. | 
|  |  | 
|  | <DT><SAMP>`Z'</SAMP> | 
|  | <DD> | 
|  | Used for template type parameters. | 
|  |  | 
|  | </DL> | 
|  |  | 
|  | <P> | 
|  | The letters <SAMP>`G'</SAMP>, <SAMP>`M'</SAMP>, <SAMP>`O'</SAMP>, and <SAMP>`p'</SAMP> | 
|  | also seem to be used for obscure purposes ... | 
|  |  | 
|  | </P> | 
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