Can we declare base class constructor or destructor as virtual?
A virtual constructor is not possible but virtual destructor is possible.
Why must base class destructors always be 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.
Can a constructor be declared as a virtual function yes or no?
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.
Can we declare destructor as virtual?
Destructors in the Base class can be Virtual. Whenever Upcasting is done, Destructors of the Base class must be made virtual for proper destrucstion of the object when the program exits. NOTE: Constructors are never Virtual, only Destructors can be Virtual.
When must a C++ destructor be declared virtual in a base class?
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.
Is destructor virtual by default C++?
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.
When should a destructor be virtual?
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.
Does abstract base class need virtual destructor?
The answer to your question is often, but not always. If your abstract class forbids clients to call delete on a pointer to it (or if it says so in its documentation), you are free to not declare a virtual destructor. Working like this, it is perfectly safe and reasonable to omit a virtual destructor.
Can constructor be virtual destructor?
2 Answers. You cannot have Virtual constructor in C++ why no virtual Constructor. Virtual destructors are useful when you can delete an instance of a derived class through a pointer to base class.
Do not invoke virtual functions from constructors or destructors?
Calling virtual functions from a constructor or destructor is considered dangerous most of the times and must be avoided whenever possible. All the C++ implementations need to call the version of the function defined at the level of the hierarchy in the current constructor and not further.
Why constructor Cannot be virtual but destructor can?
In C++, the constructor cannot be virtual, because when a constructor of a class is executed there is no virtual table in the memory, means no virtual pointer defined yet. So, the constructor should always be non-virtual. But virtual destructor is possible.
Can a constructor be virtual in C++?
Should base class destructors be virtual or non-virtual?
In most implementations, the call to the destructor will be resolved like any non-virtual code, meaning that the destructor of the base class will be called but not the one of the derived class, resulting in a resources leak. To sum up, always make base classes’ destructors virtualwhen they’re meant to be manipulated polymorphically.
When to use virtual destructors in Java?
1716 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 } };
Are pure virtual destructors legal in C++?
Pure virtual destructors are legal in standard C++ and one of the most important things to remember is that if a class contains a pure virtual destructor, it must provide a function body for the pure virtual destructor. You may be wondering why a pure virtual function requires a function body.
Should a polymorphic class have a virtual destructor?
Any class that is inherited publicly, polymorphic or not, should have a virtual destructor. To put another way, if it can be pointed to by a base class pointer, its base class should have a virtual destructor. If virtual, the derived class destructor gets called, then the base class constructor.