Accessing class members on a NULL pointer

Question

I was experimenting with C++ and found the below code as very strange.

class Foo{
public:
    virtual void say_virtual_hi(){
        std::cout << \"Vi         


        

Answer 1

In the original days of C++, the C++ code was converted to C. Object methods are converted to non-object methods like this (in your case):

foo_say_hi(Foo* thisPtr, /* other args */) 
{
}

Of course, the name foo_say_hi is simplified. For more details, look up C++ name mangling.

As you can see, if the thisPtr is never dereferenced, then the code is fine and succeeds. In your case, no instance variables or anything that depends on the thisPtr was used.

However, virtual functions are different. There's a lot of object lookups to make sure the right object pointer is passed as the paramter to the function. This will dereference the thisPtr and cause the exception.