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Why do I need a virtual destructor?

A virtual destructor is an essential entity if you use inheritance. Virtual destructor is declared in a base class. It guarantees that for all classes derived from the base class all destructors: 1) will be called and 2) will be called in proper order. It makes available a polymorphic behavior. Take a look at the snippet below:

#include "stdio.h"

class BaseClass
{
	int id;
public:
	BaseClass() { printf("BaseClass()\n"); }
	virtual ~BaseClass() { printf("~BaseClass()\n"); } //    !!!
};

class Class1 : public BaseClass
{
	int id;
public:
	Class1() { printf("Class1()\n"); }
	~Class1() { printf("~Class1()\n"); }
};

class Class2 : public Class1
{
	int id;
public:
	Class2() { printf("Class2()\n"); }
	~Class2() { printf("~Class2()\n"); }
};


int main(int argc, char* argv[])
{
	BaseClass *p = new Class2;
	delete p;

	return 0;
}

The output in case without virtual destructor is:

BaseClass()
Class1()
Class2()
~BaseClass()

But the output in case with virtual destructor differs:

BaseClass()
Class1()
Class2()
~Class2()
~Class1()
~BaseClass()

Now you see what happens if destructor should call delete() for some object/array used in the class? Resume: use virtual destructor to ensure proper memory clearing in case of using inheritance.

	Web visualcpp.net msdn.microsoft.com codeguru.com