CareerCup

I think your answer is correct and good enough.

Perfect Answer !
All the NON virtual methods will work assuming they work with zeroed out data elements -- data elements are set o 0 (via memset) and vtbl is totally destroyed (zeroed out) so none of the virtual functions would work.

It's common practice in C, to do a memset on structures, in order to initialize all member variables to some default value, usually NULL. Similarly, you can use memset to initialize class objects. But what happens if the class contains some virtual functions?

Let's take an example:

class GraphicsObject{
protected:
	char *m_pcName;
	int    m_iId;
	//etc
public:
	virtual void Draw() {}
	virtual int Area() {}
	char* Name() { return m_pcName;}
};

class Circle: public GraphicsObject{
	void Draw() { /*draw something*/ }
	int Area() { /*calculate Area*/ }
};

void main()
{
	GraphicsObject *obj = new Circle; //Create an object
	memset((void *)obj,NULL,sizeof(Circle)); //memset to 0
	obj->Name(); //Non virtual function call works fine
	obj->Draw(); //Crashes here
}

This results in a crash, because every object of a class containing virtual functions contains a pointer to the virtual function table(vtbl). This pointer is used to resolve virtual function calls, at run time and for dynamic type casting. The pointer is hidden, and is not accessible to programmers by normal means. When we do a memset, the value of this pointer also gets overwritten, which, in turn, results in a crash, if a virtual function is called.

To avoid such mysterious crashes, memset should not be used on the objects of a class with virtual functions. Instead use the default constructor or an init routine to initialize member variables.

Apparently Bloomberg guys have a fetish for low level C-style programming.

Static functions will work since they do not access data members.
About virtual functions. If a virtual function is called through the object's name (not a pointer or reference to the object) compilers can easily optimize this call so that the virtual table will not be used in run-time. Nevertheless, the behavior is undefined.

Good Question!!

Yeah i think all class members will get initilized to 0 and the call to virtual functions will lead to some undefined behavior, most probably a crash.

Nice question.