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In C++, objects are created on the stack when the constructor is invoked without the new operator, and created on the heap when the constructor is invoked with the new operator. Stack objects are deleted implicitly when they go out of scope, while heap objects must be deleted implicitly by a destructor or explicitly by using the delete operator.
Notably, a constructor is a class method as there is no object (instance) available until the object is created, but destructors, initializers, and finalizers are instance methods. Further, constructors and initializers often can accept arguments, while destructors and finalizers generally do not as they are often implicitly callable.
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.
Default constructor if no other constructor is explicitly declared. Copy constructor if no move constructor and move assignment operator are explicitly declared. If a destructor is declared generation of a copy constructor is deprecated (C++11, proposal N3242 [2]).
The rule of three (also known as the law of the big three or the big three) is a rule of thumb in C++ (prior to C++11) that claims that if a class defines any of the following then it should probably explicitly define all three: [1] destructor; copy constructor; copy assignment operator; These three functions are special member functions. If ...
Other uses, however, include calling a constructor directly, something which the C++ language does not otherwise permit. [ 3 ] The C++ language does allow a program to call a destructor directly, and, since it is not possible to destroy the object using a delete expression, that is how one destroys an object that was constructed via a pointer ...
The terminology of finalizer and finalization versus destructor and destruction varies between authors and is sometimes unclear.. In common use, a destructor is a method called deterministically on object destruction, and the archetype is C++ destructors; while a finalizer is called non-deterministically by the garbage collector, and the archetype is Java finalize methods.
The C++ standard library instead provides a dynamic array (collection) that can be extended or reduced in its std::vector template class. The C++ standard does not specify any relation between new / delete and the C memory allocation routines, but new and delete are typically implemented as wrappers around malloc and free. [6]