16.3.2 Name Mangling
Early C++ compilers mangled the names of C++ symbols so that existing
linkers could be used without modification. The cfront C++ translator
also mangled names so that information from the original C++ program
would not be lost in the translation to C. Today, name mangling remains
important for enabling overloaded function names and link-time type
checking. Here is an example C++ source file which illustrates name
mangling in action:
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class Foo
{
public:
Foo ();
void go ();
void go (int where);
private:
int pos;
};
Foo::Foo ()
{
pos = 0;
}
void
Foo::go ()
{
go (0);
}
void
Foo::go (int where)
{
pos = where;
}
int
main ()
{
Foo f;
f.go (10);
}
$ g++ -Wall example.cxx -o example.o
$ nm --defined-only example.o
00000000 T __3Foo
00000000 ? __FRAME_BEGIN__
00000000 t gcc2_compiled.
0000000c T go__3Foo
0000002c T go__3Fooi
00000038 T main
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Even though Foo contains two methods with the same name, their
argument lists (one taking an int, one taking no arguments) help
to differentiate them once their names are mangled. The
`go__3Fooi' is the version which takes an int argument. The
`__3Foo' symbol is the constructor for Foo. The GNU
binutils package includes a utility called c++filt that can
demangle names. Other proprietary tools sometimes include a similar
utility, although with a bit of imagination, you can often demangle
names in your head.
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$ nm --defined-only example.o | c++filt
00000000 T Foo::Foo(void)
00000000 ? __FRAME_BEGIN__
00000000 t gcc2_compiled.
0000000c T Foo::go(void)
0000002c T Foo::go(int)
00000038 T main
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Name mangling algorithms differ between C++ implementations so that
object files assembled by one tool chain may not be linked by another if
there are legitimate reasons to prohibit linking. This is a deliberate
move, as other aspects of the object file may make them
incompatible--such as the calling convention used for making function
calls.
This implies that C++ libraries and packages cannot be practically
distributed in binary form. Of course, you were intending to distribute
the source code to your package anyway, weren't you?
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