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6 <TITLE>G++ internals - Mangling</TITLE>
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13 <H2><A NAME="SEC20" HREF="gxxint_toc.html#TOC20">Function name mangling for C++ and Java</A></H2>
16 Both C++ and Jave provide overloaded function and methods,
17 which are methods with the same types but different parameter lists.
18 Selecting the correct version is done at compile time.
19 Though the overloaded functions have the same name in the source code,
20 they need to be translated into different assembler-level names,
21 since typical assemblers and linkers cannot handle overloading.
22 This process of encoding the parameter types with the method name
23 into a unique name is called <EM>name mangling</EM>. The inverse
24 process is called <EM>demangling</EM>.
28 It is convenient that C++ and Java use compatible mangling schemes,
29 since the makes life easier for tools such as gdb, and it eases
30 integration between C++ and Java.
34 Note there is also a standard "Jave Native Interface" (JNI) which
35 implements a different calling convention, and uses a different
36 mangling scheme. The JNI is a rather abstract ABI so Java can call methods
38 we are concerned here about a lower-level interface primarily
39 intended for methods written in Java, but that can also be used for C++
45 <H3><A NAME="SEC21" HREF="gxxint_toc.html#TOC21">Method name mangling</A></H3>
48 C++ mangles a method by emitting the function name, followed by <CODE>__</CODE>,
49 followed by encodings of any method qualifiers (such as <CODE>const</CODE>),
50 followed by the mangling of the method's class,
51 followed by the mangling of the parameters, in order.
55 For example <CODE>Foo::bar(int, long) const</CODE> is mangled
56 as <SAMP>`bar__C3Fooil'</SAMP>.
60 For a constructor, the method name is left out.
61 That is <CODE>Foo::Foo(int, long) const</CODE> is mangled
62 as <SAMP>`__C3Fooil'</SAMP>.
66 GNU Java does the same.
71 <H3><A NAME="SEC22" HREF="gxxint_toc.html#TOC22">Primitive types</A></H3>
74 The C++ types <CODE>int</CODE>, <CODE>long</CODE>, <CODE>short</CODE>, <CODE>char</CODE>,
75 and <CODE>long long</CODE> are mangled as <SAMP>`i'</SAMP>, <SAMP>`l'</SAMP>,
76 <SAMP>`s'</SAMP>, <SAMP>`c'</SAMP>, and <SAMP>`x'</SAMP>, respectively.
77 The corresponding unsigned types have <SAMP>`U'</SAMP> prefixed
78 to the mangling. The type <CODE>signed char</CODE> is mangled <SAMP>`Sc'</SAMP>.
82 The C++ and Java floating-point types <CODE>float</CODE> and <CODE>double</CODE>
83 are mangled as <SAMP>`f'</SAMP> and <SAMP>`d'</SAMP> respectively.
87 The C++ <CODE>bool</CODE> type and the Java <CODE>boolean</CODE> type are
88 mangled as <SAMP>`b'</SAMP>.
92 The C++ <CODE>wchar_t</CODE> and the Java <CODE>char</CODE> types are
93 mangled as <SAMP>`w'</SAMP>.
97 The Java integral types <CODE>byte</CODE>, <CODE>short</CODE>, <CODE>int</CODE>
98 and <CODE>long</CODE> are mangled as <SAMP>`c'</SAMP>, <SAMP>`s'</SAMP>, <SAMP>`i'</SAMP>,
99 and <SAMP>`x'</SAMP>, respectively.
103 C++ code that has included <CODE>javatypes.h</CODE> will mangle
104 the typedefs <CODE>jbyte</CODE>, <CODE>jshort</CODE>, <CODE>jint</CODE>
105 and <CODE>jlong</CODE> as respectively <SAMP>`c'</SAMP>, <SAMP>`s'</SAMP>, <SAMP>`i'</SAMP>,
106 and <SAMP>`x'</SAMP>. (This has not been implemented yet.)
111 <H3><A NAME="SEC23" HREF="gxxint_toc.html#TOC23">Mangling of simple names</A></H3>
114 A simple class, package, template, or namespace name is
115 encoded as the number of characters in the name, followed by
116 the actual characters. Thus the class <CODE>Foo</CODE>
117 is encoded as <SAMP>`3Foo'</SAMP>.
121 If any of the characters in the name are not alphanumeric
122 (i.e not one of the standard ASCII letters, digits, or '_'),
123 or the initial character is a digit, then the name is
124 mangled as a sequence of encoded Unicode letters.
125 A Unicode encoding starts with a <SAMP>`U'</SAMP> to indicate
126 that Unicode escapes are used, followed by the number of
127 bytes used by the Unicode encoding, followed by the bytes
128 representing the encoding. ASSCI letters and
129 non-initial digits are encoded without change. However, all
130 other characters (including underscore and initial digits) are
131 translated into a sequence starting with an underscore,
132 followed by the big-endian 4-hex-digit lower-case encoding of the character.
136 If a method name contains Unicode-escaped characters, the
137 entire mangled method name is followed by a <SAMP>`U'</SAMP>.
141 For example, the method <CODE>X\u0319::M\u002B(int)</CODE> is encoded as
142 <SAMP>`M_002b__U6X_0319iU'</SAMP>.
147 <H3><A NAME="SEC24" HREF="gxxint_toc.html#TOC24">Pointer and reference types</A></H3>
150 A C++ pointer type is mangled as <SAMP>`P'</SAMP> followed by the
151 mangling of the type pointed to.
155 A C++ reference type as mangled as <SAMP>`R'</SAMP> followed by the
156 mangling of the type referenced.
160 A Java object reference type is equivalent
161 to a C++ pointer parameter, so we mangle such an parameter type
162 as <SAMP>`P'</SAMP> followed by the mangling of the class name.
167 <H3><A NAME="SEC25" HREF="gxxint_toc.html#TOC25">Qualified names</A></H3>
170 Both C++ and Java allow a class to be lexically nested inside another
171 class. C++ also supports namespaces (not yet implemented by G++).
172 Java also supports packages.
176 These are all mangled the same way: First the letter <SAMP>`Q'</SAMP>
177 indicates that we are emitting a qualified name.
178 That is followed by the number of parts in the qualified name.
179 If that number is 9 or less, it is emitted with no delimiters.
180 Otherwise, an underscore is written before and after the count.
181 Then follows each part of the qualified name, as described above.
185 For example <CODE>Foo::\u0319::Bar</CODE> is encoded as
186 <SAMP>`Q33FooU5_03193Bar'</SAMP>.
191 <H3><A NAME="SEC26" HREF="gxxint_toc.html#TOC26">Templates</A></H3>
194 A class template instantiation is encoded as the letter <SAMP>`t'</SAMP>,
195 followed by the encoding of the template name, followed
196 the number of template parameters, followed by encoding of the template
197 parameters. If a template parameter is a type, it is written
198 as a <SAMP>`Z'</SAMP> followed by the encoding of the type.
202 A function template specialization (either an instantiation or an
203 explicit specialization) is encoded by an <SAMP>`H'</SAMP> followed by the
204 encoding of the template parameters, as described above, followed by
205 an <SAMP>`_'</SAMP>, the encoding of the argument types template function (not the
206 specialization), another <SAMP>`_'</SAMP>, and the return type. (Like the
207 argument types, the return type is the return type of the function
208 template, not the specialization.) Template parameters in the argument
209 and return types are encoded by an <SAMP>`X'</SAMP> for type parameters, or a
210 <SAMP>`Y'</SAMP> for constant parameters, and an index indicating their position
211 in the template parameter list declaration.
216 <H3><A NAME="SEC27" HREF="gxxint_toc.html#TOC27">Arrays</A></H3>
219 C++ array types are mangled by emitting <SAMP>`A'</SAMP>, followed by
220 the length of the array, followed by an <SAMP>`_'</SAMP>, followed by
221 the mangling of the element type. Of course, normally
222 array parameter types decay into a pointer types, so you
227 Java arrays are objects. A Java type <CODE>T[]</CODE> is mangled
228 as if it were the C++ type <CODE>JArray<T></CODE>.
229 For example <CODE>java.lang.String[]</CODE> is encoded as
230 <SAMP>`Pt6JArray1ZPQ34java4lang6String'</SAMP>.
235 <H3><A NAME="SEC28" HREF="gxxint_toc.html#TOC28">Table of demangling code characters</A></H3>
238 The following special characters are used in mangling:
245 Indicates a C++ array type.
249 Encodes the C++ <CODE>bool</CODE> type,
250 and the Java <CODE>boolean</CODE> type.
254 Encodes the C++ <CODE>char</CODE> type, and the Java <CODE>byte</CODE> type.
258 A modifier to indicate a <CODE>const</CODE> type.
259 Also used to indicate a <CODE>const</CODE> member function
260 (in which cases it precedes the encoding of the method's class).
264 Encodes the C++ and Java <CODE>double</CODE> types.
268 Indicates extra unknown arguments <CODE>...</CODE>.
272 Encodes the C++ and Java <CODE>float</CODE> types.
276 Used to indicate a function type.
280 Used to indicate a template function.
284 Encodes the C++ and Java <CODE>int</CODE> types.
288 Indicates a complex type.
292 Encodes the C++ <CODE>long</CODE> type.
296 Indicates a pointer type. Followed by the type pointed to.
300 Used to mangle qualified names, which arise from nested classes.
301 Should also be used for namespaces (?).
302 In Java used to mangle package-qualified names, and inner classes.
306 Encodes the GNU C++ <CODE>long double</CODE> type.
310 Indicates a reference type. Followed by the referenced type.
314 Encodes the C++ and java <CODE>short</CODE> types.
318 A modifier that indicates that the following integer type is signed.
319 Only used with <CODE>char</CODE>.
321 Also used as a modifier to indicate a static member function.
325 Indicates a template instantiation.
329 A back reference to a previously seen type.
333 A modifier that indicates that the following integer type is unsigned.
334 Also used to indicate that the following class or namespace name
335 is encoded using Unicode-mangling.
339 Encodes the C++ and Java <CODE>void</CODE> types.
343 A modified for a <CODE>const</CODE> type or method.
347 Encodes the C++ <CODE>wchar_t</CODE> type, and the Java <CODE>char</CODE> types.
351 Encodes the GNU C++ <CODE>long long</CODE> type, and the Java <CODE>long</CODE> type.
355 Encodes a template type parameter, when part of a function type.
359 Encodes a template constant parameter, when part of a function type.
363 Used for template type parameters.
368 The letters <SAMP>`G'</SAMP>, <SAMP>`M'</SAMP>, <SAMP>`O'</SAMP>, and <SAMP>`p'</SAMP>
369 also seem to be used for obscure purposes ...
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