Question

conv.h

class Base 
{
public:
    void foo();
};

class Derived: public Base 
{
public:
    void bar();
};

class A {};
class B 
{
public:
    void koko();
};

conv.cpp

void Base::foo()
{
    cout<<"stamm";
}

void Derived::bar()
{
    cout<<"bar shoudn't work"<<endl;
}
void B::koko()
{
    cout<<"koko shoudn't work"<<endl;
}

main.cpp

#include "conv.h"
#include <iostream>
int main()
{   
    Base * a = new Base;
    Derived * b = static_cast<Derived*>(a);
    b->bar();

    Derived * c = reinterpret_cast<Derived*>(a);
    c->bar();

    A* s1 = new A;
    B* s2 = reinterpret_cast<B*>(s1);
    s2->koko();
}

output:

bar shoudn't work
bar shoudn't work
koko shoudn't work

How come the method bar is succeeded to be called in run time despite that I have created a Base class not derived?? it works even with two types of conversions (static and reinterpret cast).

same question as above but with unrelated classes (A & B) ??

Answer 1

It’s working (read: “compiling and not crashing”) ’cause you never use the this pointer in your nominally “member” functions. If you tried to print out a member variable, for example, you’d get the garbage output or crashes you expect – but these functions as they are now don’t depend on anything in the classes they’re supposedly part of. this could even be NULL for all they care.