What is a virtual function in C++?

A C++ virtual function is a member function in the base class that you redefine in a derived class. It is declared using the virtual keyword. When the function is made virtual, C++ determines which function is to be invoked at the runtime based on the type of the object pointed by the base class pointer.

How are virtual functions implemented in C++?

To implement virtual functions, C++ uses a special form of late binding known as the virtual table. The virtual table is a lookup table of functions used to resolve function calls in a dynamic/late binding manner.

What is pure virtual function in CPP?

A pure virtual function is a virtual function in C++ for which we need not to write any function definition and only we have to declare it. It is declared by assigning 0 in the declaration. If an Abstract Class has derived class, they must implement all pure virtual functions, or else they will become Abstract too.

What is an interface in CPP?

An interface describes the behavior or capabilities of a C++ class without committing to a particular implementation of that class. Thus, if a subclass of an ABC needs to be instantiated, it has to implement each of the virtual functions, which means that it supports the interface declared by the ABC.

What is polymorphism CPP?

Polymorphism in C++ means, the same entity (function or object) behaves differently in different scenarios. Consider this example: The “ +” operator in c++ can perform two specific functions at two different scenarios i.e when the “+” operator is used in numbers, it performs addition.

How do you create an interface in CPP?

And like other answers:

Make a class with pure virtual methods.
Use the interface by creating another class that overrides those virtual methods. class IDemo { public: virtual void OverrideMe() = 0; virtual ~IDemo() {} } Or class IDemo { public: virtual void OverrideMe() = 0; protected: ~IDemo() {} }

What is friend function CPP?

A friend function in C++ is defined as a function that can access private, protected and public members of a class. The friend function is declared using the friend keyword inside the body of the class.

Why interface is used in CPP?

An interface describes the behavior or capabilities of a C++ class without committing to a particular implementation of that class. The purpose of an abstract class (often referred to as an ABC) is to provide an appropriate base class from which other classes can inherit.

What are interfaces in CPP?

An interface is a description of what member functions must a class, which inherits this interface, implement. In other words, an interface describes behavior of the class. You can imagine an interface as a list of functions that must be implemented by a class.

Which is false about friend function?

Explanation: Friend functions are not in the scope of a class and hence cannot be called through a class object. A friend function can access all types of members of the class.

What is the use of virtual function?

Virtual functions ensure that the correct function is called for an object, regardless of the type of reference (or pointer) used for function call. They are mainly used to achieve Runtime polymorphism. Functions are declared with a virtual keyword in base class.

Can you call a virtual function from a constructor?

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. You can call a virtual function in a constructor.