Cpp virtual function testcase

derivce.cpp

#include <iostream>

using namespace std;

class Base1 {
    public:
        virtual void f() {  cout << "Base1:f" <<  endl;}
        virtual void g() { cout << "Base1::g" <<  endl;}
};


class Base2 {
    public:
        virtual void f() {  cout << "Base2:f" <<  endl;}
        virtual void g() { cout << "Base2::g" <<  endl;}
};

class Base3 {
    public:
        virtual void f() {  cout << "Base3:f" <<  endl;}
        virtual void g() { cout << "Base3::g" <<  endl;}
};

class Derive : public Base1, public Base2, public Base3 {
    public:
        virtual void f() { cout << "Derive::f" <<  endl;}
        virtual void g1() { cout << "Derive::g1" <<  endl;}
};

typedef void(*Func)(void);

int main() {
    Func pFun = NULL;
    Derive d;
    long **pVtab = (long**)&d;

    // first virtual func table
    pFun = (Func)pVtab[0][0];
    pFun();

    pFun = (Func)pVtab[0][1];
    pFun();

    pFun = (Func)pVtab[0][2];
    pFun();

    pFun = (Func)pVtab[1][0];
    pFun();

    pFun = (Func)pVtab[1][1];
    pFun();

    pFun = (Func)pVtab[2][0];
    pFun();

    pFun = (Func)pVtab[2][1];
    pFun();

    return 0;
}

// output:
// Derive::f
// Base1::g
// Derive::g1
// Derive::f
// Base2::g
// Derive::f
// Base3::g

According to this post

Non-virtual function will not exist in virtual function table. Because it's decided in compile-time.

cpp is not memory-safe. Non-public function will exist in virtual function table. By offset the pointer, we can call them.