Using C++ DLLs with different compiler versions

Question

This question is related to \"How to make consistent dll binaries across VS versions ?\"

• We have applications and DLLs built with VC6 and a new application bui

Answer 1

Interface member names will not be decorated -- they're just offsets in a vtable. You can define an interface (using a C struct, rather than a COM "interface") in a header file, thusly:

struct IFoo {
    int Init() = 0;
};

Then, you can export a function from the DLL, with no mangling:

class CFoo : public IFoo { /* ... */ };
extern "C" IFoo * __stdcall GetFoo() { return new CFoo(); }

This will work fine, provided that you're using a compiler that generates compatible vtables. Microsoft C++ has generated the same format vtable since (at least, I think) MSVC6.1 for DOS, where the vtable is a simple list of pointers to functions (with thunking in the multiple-inheritance case). GNU C++ (if I recall correctly) generates vtables with function pointers and relative offsets. These are not compatible with each other.