What is the purpose of virtual destructor?

What is the purpose of virtual destructor?

A virtual destructor is used to free up the memory space allocated by the derived class object or instance while deleting instances of the derived class using a base class pointer object.

When must a C++ destructor be declared virtual in a base 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.

What is a virtual destructor explain with an example?

Deleting a derived class object using a pointer of base class type that has a non-virtual destructor results in undefined behavior. To correct this situation, the base class should be defined with a virtual destructor. For example, following program results in undefined behavior.

Why does a class destructor sometimes have to be specified as virtual?

The implicitly-declared destructor is virtual (because the base class has a virtual destructor) and the lookup for the deallocation function (operator delete()) results in a call to ambiguous, deleted, or inaccessible function.

Can virtual function friend?

A virtual function can be a friend function of another class. They are always defined in the base class and overridden in a derived class. It is not mandatory for the derived class to override (or re-define the virtual function), in that case, the base class version of the function is used.

Are default destructors virtual?

No, all destructor’s are by default NOT virtual. In addition to that. In practice, it’s usually a good idea to define a class with a virtual destructor if you think that someone might eventually create a derived class from it.

Can a constructor be virtual?

Constructor can not be virtual, because when constructor of a class is executed there is no vtable in the memory, means no virtual pointer defined yet. Hence the constructor should always be non-virtual.

Why C++ destructors are generally declared virtual?

Virtual destructors in C++ are used to avoid memory leaks especially when your class contains unmanaged code, i.e., contains pointers or object handles to files, databases or other external objects. A destructor can be virtual.

How do you know that your class needs a virtual destructor?

Virtual destructors are useful when you might potentially delete an instance of a derived class through a pointer to base class: class Base { // some virtual methods }; class Derived : public Base { ~Derived() { // Do some important cleanup } };

Should all destructors be virtual?

Destructor is part of the interface and expected to implemented. Therefore destructor should be pure virtual. How about constructor? Constructor is actually not part of the interface because object is always instantiated explicitly.

Are virtual destructors inherited?

Yes, they are the same. The derived class not declaring something virtual does not stop it from being virtual.

Can a virtual function be friend of another class?

When to use virtual destructors in C + +?

When to use virtual destructors in C++? If a class has any virtual function, it should have a virtual destructor, and that classes not designed to be base classes or not designed to be used polymorphically should not declare virtual destructors. So you should declare destructors virtual in polymorphic base classes.

What happens if the base destructor is not virtual?

If Base’s destructor is not virtual then delete b has undefined behavior in this case. The call to the destructor will be resolved like any non-virtual code. So the destructor of the base class will be called but not the one of the derived class, this will result in a resources leak.

When to call a destructor for a non-virtual class?

The destructors for non-virtual base classes are called in the reverse order in which the base class names are declared. Consider the following class declaration: C++. class MultInherit : public Base1, public Base2 In the preceding example, the destructor for Base2 is called before the destructor for Base1.

When to declare destructors virtual in polymorphic base classes?

So you should declare destructors virtual in polymorphic base classes. This is because if you create an object of base class using a derived constructor − If Base’s destructor is not virtual then delete b has undefined behavior in this case. The call to the destructor will be resolved like any non-virtual code.