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Virtual functions allow a program to call methods that don't necessarily even exist at the moment the code is compiled. [citation needed] In C++, virtual methods are declared by prepending the virtual keyword to the function's declaration in the base class. This modifier is inherited by all implementations of that method in derived classes ...
In computer programming, a virtual method table (VMT), virtual function table, virtual call table, dispatch table, vtable, or vftable is a mechanism used in a programming language to support dynamic dispatch (or run-time method binding).
Any derived class inherits the virtual function as pure and must provide a non-pure definition of it (and all other pure virtual functions) before objects of the derived class can be created. A program that attempts to create an object of a class with a pure virtual member function or inherited pure virtual member function is ill-formed.
The default form of dispatch is static. To get dynamic dispatch the programmer must declare a method as virtual. C++ compilers typically implement dynamic dispatch with a data structure called a virtual function table (vtable) that defines the name-to-implementation mapping for a given class as a set of member function pointers. This is purely ...
For example, in C++ a method is known as a member function. C++ also has the concept of virtual functions which are member functions that can be overridden in derived classes and allow for dynamic dispatch.
In C++, late binding (also called "dynamic binding") refers to what normally happens when the virtual keyword is used in a method's declaration. C++ then creates a so-called virtual table , which is a look-up table for such functions that will always be consulted when they are called.
To elaborate on the above example, consider a base class with no virtual functions. Whenever the base class calls another member function, it will always call its own base class functions. When we derive a class from this base class, we inherit all the member variables and member functions that were not overridden (no constructors or destructors).
The function is virtual and is called virtually. Direct calls to virtual functions can be inlined. The program takes the address of the function and the call is made via the pointer to the function. Direct calls to functions that have had their address taken can be inlined. The function is also marked with the naked __declspec modifier.
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