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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.
A virtual call requires at least an extra indexed dereference and sometimes a "fixup" addition, compared to a non-virtual call, which is simply a jump to a compiled-in pointer. Therefore, calling virtual functions is inherently slower than calling non-virtual functions.
Virtual class; Virtual function (also called virtual method) Virtual function pointer (also called virtual method pointer) Virtual inheritance (Object Oriented Programming) Virtual method table (also called vtable, virtual function table or virtual method table) Viscosity (programming) Void type
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++ 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.
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 ...
Friend: C++ supports a mechanism where a function explicitly declared as a friend function of the class may access the members designated as private or protected. [15] Path-based: Java supports restricting access to a member within a Java package, which is the logical path of the file. However, it is a common practice when extending a Java ...
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 ...