Why is destructor virtual in c

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This is undesirable behaviour as the operating system has no mechanism to regain the lost memory because it does not have any references to its location! Since memory is a finite resource, if this leak persists over continued program usage, eventually there will be no available RAM random access memory to carry out other programs.

For instance, consider a pointer to a base class such as PayOff being assigned to a derived class object address via a reference. If the object that the pointer is pointing to is deleted, and the destructor is not set to virtual , then the base class destructor will be called instead of the derived class destructor. This can lead to a memory leak. Consider the following code:. What is happening here?

Firstly, we create a base class called Base and a subclass called Derived. The destructors are NOT set to virtual. When someone will delete a derived-class object via a base-class pointer. In particular, here's when you need to make your destructor virtual : if someone will derive from your class, and if someone will say new Derived , where Derived is derived from your class, and if someone will say delete p , where the actual object's type is Derived but the pointer p 's type is your class.

Here's a simplified rule of thumb that usually protects you and usually doesn't cost you anything: make your destructor virtual if your class has any virtual functions. Rationale: that usually protects you because most base classes have at least one virtual function. In other words, you've already paid all the per-object space-cost that you'll ever pay once you add the first virtual function, so the virtual destructor doesn't add any additional per-object space cost.

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