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For this reason, calling virtual functions in constructors is generally discouraged. In C++, the "base" function is called. Specifically, the most derived function that is not more derived than the current constructor or destructor's class is called. [7]: §15.7.3 [8] [9] If that function is a pure virtual function, then undefined behavior occurs.
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).
In C++ implementations, this is commonly done using virtual function tables. If the object type is known, this may be bypassed by prepending a fully qualified class name before the function call, but in general calls to virtual functions are resolved at run time.
Virtual functions are the means by which a C++ class can achieve polymorphic behavior. Non-virtual member functions, or regular methods, are those that do not participate in polymorphism. C++ Example:
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 ...
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.
Like virtual functions, virtual classes follow the same rules of definition, overriding, and reference. [2] When a derived class inherits from a base class, it must define or override the virtual inner classes it inherited from the base class. An object of the child class may be referred to by a reference or pointer of the parent class type or ...
Virtual inheritance is a C++ technique that ensures only one copy of a base class ' s member variables are inherited by grandchild derived classes. Without virtual inheritance, if two classes B and C inherit from a class A , and a class D inherits from both B and C , then D will contain two copies of A ' s member variables: one via B , and one ...