Write a Program Where the Destructors Should Be Virtual.Explain

Question

Examlex · Accepted Answer

The Answer is The requested code and further discussion follow.
#include
using namespace std;
class B
{
public:
B():bPtr( new int[5]){ cout << "allocates 5 ints ";}
virtual ~B()
{ delete[] bPtr;cout << "deallocates 5 ints ";}
private:
int * bPtr;
};
class D:public B
{
public:
D():B(),dPtr(new int[1000]){cout << "allocates 1000 ints ";}
~D(){ delete[] dPtr;cout << "deallocates 1000 ints ";}
private:
int * dPtr;
};
int main()
{
for (int i = 0;i < 100;i++)
{
B* bPtr = new D;
delete bPtr;
}
cout << " Without virtual destructor, ";
cout << "100 * 1000 + 500 ints allocated "
<< "but only 500 ints deallocated. ";
cout << " With virtual destructor, ";
cout << "100 * 1000 + 500 ints allocated,and "
<< "100 * 1000 + 500 ints deallocated. ";
}
In this code,if the base class destructor is not virtual,the system must bind the pointer to the destructor at compile time.The pointer in main,bPtr,is of type B*,i.e. ,pointer to B,so it is bound to B's member functions.The destructor for D,~D fails to run.
If the keyword virtual is removed from the destructor in the base class,class B,the derived class destructor ~D is not called.Approximately 400K of memory would then be leaked.

Write a Program Where the Destructors Should Be Virtual.Explain

Definitions: