Question

I am writing a DLL with mixed C/C++ code. I want to specify the ordinals of the functions I’m exporting. So I created a .DEF file that looks like this

LIBRARY LEONMATH  EXPORTS      sca_alloc   @1     vec_alloc   @2     mat_alloc   @3      sca_free    @4     vec_free    @5     mat_free    @6      ... 

I would like to specify the ordinals of my C++ functions and class methods too. I have tried using the Dependency Walker to add the mangled names of my functions to the .DEF file:

    ??0CScalar@@QAE@XZ      @25     ??0CScalar@@QAE@O@Z     @26     ??0CScalar@@QAE@ABV0@@Z @27     ??1CScalar@@QAE@XZ      @28 

But this has failed. Any ideas why this could be happening?

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EDIT: kauppi made a good observation, so I’m adding more information to the question.

• Platform: Windows (and I’m not interested in portability)
• Compiler: Microsoft’s C++ compiler (I’m using VS2005)
• Why I want to do this?: Using the ordinals has the advantage of letting me call exported C++ functions from C code.

Answer 1

Well, I don’t have experience with ordinals (which look like some ugly, compiler-specific thing), but I can help you with making C++/C code compatible.

Suppose, in C++, that your header file looks like this:

class MyClass {     void foo(int);     int bar(int);     double bar(double);     void baz(MyClass); }; 

You can make it C-compatible by doing the following:

#ifdef __cplusplus #define EXTERN_C extern 'C' // Class definition here; unchanged #else #define EXTERN_C typedef struct MyClass MyClass; #endif  EXTERN_C void MyClass_foo (MyClass*, int); EXTERN_C int MyClass_bar_int (MyClass*, int); EXTERN_C double MyClass_bar_double (MyClass*, double); EXTERN_C void MyClass_baz (MyClass*, MyClass*); 

In the C++ source file, you just define the various extern 'C' functions to pass to the desired member functions, like this (this is only one; the rest work similarly)

extern 'C' void MyClass_foo (MyClass* obj, int i) {   obj->foo(i); } 

The code will then have a C interface, without having to change the C++ code at all (except for declarations in the header; but those could also be moved to another file 'myclass_c.h' or the like). All the functions declared/defined extern ‘C’ won’t be mangled, so you can do other operations on them easily. You will also probably want functions to construct/destroy instances of MyClass (you can, of course, use new/delete for this).