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When an object is created, a pointer to this table, called the virtual table pointer, vpointer or VPTR, is added as a hidden member of this object. As such, the compiler must also generate "hidden" code in the constructors of each class to initialize a new object's virtual table pointer to the address of its class's virtual method table.
In object-oriented programming, a destructor (sometimes abbreviated dtor [1]) is a method which is invoked mechanically just before the memory of the object is released. [2] It can happen when its lifetime is bound to scope and the execution leaves the scope, when it is embedded in another object whose lifetime ends, or when it was allocated dynamically and is released explicitly.
Languages differ in their behavior while the constructor or destructor of an object is running. 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.
This comparison of programming languages compares how object-oriented programming languages such as C++, Java, Smalltalk, Object Pascal, Perl, Python, and others manipulate data structures. Object construction and destruction
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).
C++ also allows a single instance of the multiple class to be created via the virtual inheritance mechanism (i.e. Worker::Human and Musician::Human will reference the same object). Common Lisp CLOS attempts to provide both reasonable default behavior and the ability to override it.
Aspects of object lifetime vary between programming languages and within implementations of a language. The core concepts are relatively common, but terminology varies. For example, the concepts of create and destroy are sometimes termed construct and destruct and the language elements are termed constructor (ctor) and destructor (dtor).
In C++, the name of the constructor is the name of the class. It returns nothing. It can have parameters like any member function. Constructor functions are usually declared in the public section, but can also be declared in the protected and private sections, if the user wants to restrict access to them. The constructor has two parts.