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Constructor (object-oriented programming) In class-based, object-oriented programming, a constructor (abbreviation: ctor) is a special type of function called to create an object. It prepares the new object for use, often accepting arguments that the constructor uses to set required member variables.
In the C++ programming language, special member functions[1] are functions which the compiler will automatically generate if they are used, but not declared explicitly by the programmer. The automatically generated special member functions are: Default constructor if no other constructor is explicitly declared.
On the contrary, instance initializers are automatically called before the call to a constructor every time an instance of the class is created. Unlike constructors instance initializers cannot take any arguments and generally they cannot throw any checked exceptions (except in several special cases). Instance initializers are declared in a ...
Appearance. hide. In object-oriented programming, inheritance is the mechanism of basing an object or class upon another object (prototype-based inheritance) or class (class-based inheritance), retaining similar implementation. Also defined as deriving new classes (sub classes) from existing ones such as super class or base class and then ...
A constructor is a method that is called at the beginning of an object's lifetime to create and initialize the object, a process called construction (or instantiation). Initialization may include an acquisition of resources. Constructors may have parameters but usually do not return values in most languages. See the following example in Java:
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.
This constructor is a special kind of constructor, called an initializer-list-constructor. Classes with such a constructor are treated specially during uniform initialization (see below ) The template class std::initializer_list<> is a first-class C++11 standard library type.
The destructor is called when the object is being collected by the garbage collector to perform some manual clean-up. There is a default destructor method called finalize that can be overridden by declaring one. The syntax is similar to the one of constructors. The difference is that the name is preceded by a ~ and it cannot contain any parameters.