Calling Virtual function from V-table [closed]

Question

As all the virtual function in C++ is stored in V-table. Overiding takes place in the case of virtual function. I want to ask there is any way by which we can call the Virtual function directly from the table and able too determined what functions V-table contains.

Answer 1

Well, actually you can. I don't care about portability, but in VS you can do it. Assuming that we are building 32-bit code with VS, the first 4 bytes at the objects address is the vtable address. By looking at the header files we know the order of methods in the vtable.

Example:

class Base
{
public:

    virtual void printMessage()
    {
        std::cout << "Base::printMessage()" << std::endl;
    }
};

class Derived : public Base
{
public:

    void printMessage()
    {
        std::cout << "Derived::printMessage()" << std::endl;
    }
};

int main(int argc, char* argv[])
{
    Derived d;

    unsigned int vtblAddress = *(unsigned int*)&d;

    typedef void(*pFun)(void*);

    pFun printFun = (pFun)(*(unsigned int*)(vtblAddress));

    printFun(&d);

    return 0;
}

P.S. I'm not going to ask why are you doing it, but here you have one option :-)

Answer 2

There is no guarantee by standard, that virtual functions are implemented using v-table. So, only if you are sure, that compiler use v-table - you can find needed offset.