What's the best way to call a member function if you have an object and a bare function pointer pointing to the member? Essentially I want to call the function pointer with thiscall calling convention.
Background: I'm looking up symbols in a shared library dynamically, obtaining a factory function pointer and a pointer to a certain member function I want to call. The member function itself is not virtual. I have no control over the shared library, I just have the binary.
Example:
typedef void * (*GenericFptr)();
GenericFptr lookup(const char *);
class CFoo;
GenericFptr factoryfn(lookup("CFoo factory function"));
CFoo *foo = reinterpret_cast<CFoo *>(factoryfn());
GenericFptr memberfn(lookup("CFoo member function"));
// now invoke memberfn on foo
Currently I'm using an union to convert the function pointer to a pointer to member function. It's ugly and creates dependencies to compiler implementation details:
class CFoo {
public:
void *dummy() { return 0; }
};
typedef void * (CFoo::*FooMemberPtr)();
union {
struct {
// compiler-specific layout for pointer-to-member
void *x, *y;
GenericFptr ptr;
} fnptr;
FooMemberPtr memberfn;
} f;
f.memberfn = &CFoo::dummy; // init pointer-to-member
f.fnptr.ptr = memberfn; // rewrite pointer
void *result = (foo->*f.memberfn)();
