C++ compiler creates a hidden class member called virtual-pointer or in short vptr when there are one or more virtual functions. This vptr is a pointer that points to a table of function pointers. This table is also created by compiler and called virtual function table or vtable.
What is virtual table in C++?
Runtime Polymorphism is C++ is achived with virtual function. As the class contains a virtual function C++ compiler inserts a pointer v_ptr called as virtual table pointer. Compiler also creates a table for that class called as virtual table known as vtable for the class.
Why destructor can be virtual?
If your derived class destructor is virtual then objects will be destrcuted in a order(firstly derived object then base ). If your derived class destructor is NOT virtual then only base class object will get deleted(because pointer is of base class “Base *myObj”). So there will be memory leak for derived object.
Why do we need pure virtual function in C++?
“Briefly, it’s to make the class abstract, so that it can’t be instantiated, but a child class can override the pure virtual methods to form a concrete class. This is a good way to define an interface in C++.” Non-abstract classes can contain virtual member functions and be instantiated.
What is a pure virtual function in C++?
A pure virtual function is a virtual function whose declaration ends in =0 : Derived classes need to override/implement all inherited pure virtual functions. If they do not, they too will become abstract. An interesting ‘feature’ of C++ is that a class can define a pure virtual function that has an implementation.
What do you mean by encapsulation in C++?
Encapsulation is a process of combining data members and functions in a single unit called class. This is to prevent the access to the data directly, the access to them is provided through the functions of the class. It is one of the popular feature of Object Oriented Programming(OOPs) that helps in data hiding.
What is a virtual function in C++?
A virtual function is a member function that you expect to be redefined in derived classes. When you refer to a derived class object using a pointer or a reference to the base class, you can call a virtual function for that object and execute the derived class’s version of the function.
Why do we use virtual functions?
Virtual Functions are used to support ” Run time Polymorphism”. When the virtual function is called by using a Base Class Pointer, the Compiler decides at Runtime which version of the function i.e. Base Class version or the overridden Derived Class version is to be called. This is called Run time Polymorphism.
What is runtime polymorphism in oops?
The most common use of polymorphism in OOP occurs when a parent class reference is used to refer to a child class object. Dynamic Binding/Runtime Polymorphism : Run time Polymorphism also known as method overriding. In this Mechanism by which a call to an overridden function is resolved at a Run-Time.
What is meant by pure virtual function in C++?
A pure virtual function or pure virtual method is a virtual function that is required to be implemented by a derived class if the derived class is not abstract. Classes containing pure virtual methods are termed “abstract” and they cannot be instantiated directly.
What is a VPTR and Vtable in C++?
C++ compiler creates a hidden class member called virtual-pointer or in short vptr when there are one or more virtual functions. This vptr is a pointer that points to a table of function pointers. Each row of the vtable is a function pointer pointing to a corresponding virtual function.
What is the use of friend class in C++?
A friend class is a class all of whose member functions are friend functions of a class, that is, whose member functions have access to the other class’s private and protected members.
What is a Vtable in C++?
V-tables (or virtual tables) are how most C++ implementations do polymorphism. For each concrete implementation of a class, there is a table of function pointers to all the virtual methods. A pointer to this table (called the virtual table) exists as a data member in all the objects.
What is the use of a destructor?
Destructor” functions are the inverse of constructor functions. They are called when objects are destroyed (deallocated). Designate a function as a class’s destructor by preceding the class name with a tilde ( ~ ). In a /clr compilation, the destructor has a special role in releasing managed and unmanaged resources.
How can we achieve run time polymorphism in C++?
Runtime time polymorphism is done using inheritance and virtual functions. Polymorphism means that functions assume different forms at different times. In case of compile time it is called function overloading. The compiler will select the right function depending on the type of parameters passed.
Why do we need a virtual function in C++?
Virtual Functions are used to support Run time Polymorphism. When the virtual function is called by using a Base class pointer, the compiler decides at run-time which version of the function – i.e. the Base class version or the overridden Derived class version – is to be called.
What is the use of this pointer?
Every object in C++ has access to its own address through an important pointer called this pointer. The this pointer is an implicit parameter to all member functions. Therefore, inside a member function, this may be used to refer to the invoking object.
What is a virtual class?
In object-oriented programming, a virtual class is a nested inner class whose functions and member variables can be overridden and redefined by subclasses of an outer class. Virtual classes are analogous to virtual functions. (Just like the run time type of an object decides which virtual function should be used.)
What is the use of inline function in C++?
The inline functions are a C++ enhancement feature to increase the execution time of a program. Functions can be instructed to compiler to make them inline so that compiler can replace those function definition wherever those are being called.
What is a virtual table in a database?
SQL CREATE VIEW Statement. In SQL, a view is a virtual table based on the result-set of an SQL statement. A view contains rows and columns, just like a real table. The fields in a view are fields from one or more real tables in the database.