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Constructor cannot be virtual but destructor can be virtual justify?
Chtnphrk
bcoz constructor cant be invoked
Wiki User
∙ 10y ago
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How can you create a virtual copy constructor?
You cannot. Constructors are specific to the class in which they are declared. They cannot be inherited and so they cannot be virtual.
What is the difference between the constructor to and destructor?
Functions and Constructors are similar in many ways. They can have arguments, they can have any amount of code, they can access the class's variables etc. the only difference is that a method in java needs to mandatorily have a return type but a Constructor in java cannot have a return type. It always creates and returns an object of the class for which it is the constructor. You cannot return a value from a constructor explicitly and if you try to do that, the compiler will give an error. The system knows that the purpose of the constructor is to create an object of the class and it will do the same irrespective of whether you declare a return type or not.
Can a constructor be declared as virtual?
A constructor cannot be virtual because at the time when the constructor is invoked the virtual table would not be available in the memory. Hence we cannot have a virtual constructor. ## Constructor called implicitly not explicitly so constructor is not virtual.
Can you overload destructor for your class?
No. Classes can only have one destructor, whether you define one yourself or allow the compiler to generate one for you. The compiler-generated destructor is public by default, does not release any memory allocated to any class' member pointers, and is non-virtual, which are the three main reasons for defining your own.
What are virtual constructors or destructors?
If an object (with a non-virtual destructor) is destroyed explicitly by applying the delete operator to a base-class pointer to the object, the base-class destructor function (matching the pointer type) is called on the object. There is a simple solution to this problem
How can you create a virtual copy constructor?
You cannot. Constructors are specific to the class in which they are declared. They cannot be inherited and so they cannot be virtual.
What is the difference between the constructor to and destructor?
Functions and Constructors are similar in many ways. They can have arguments, they can have any amount of code, they can access the class's variables etc. the only difference is that a method in java needs to mandatorily have a return type but a Constructor in java cannot have a return type. It always creates and returns an object of the class for which it is the constructor. You cannot return a value from a constructor explicitly and if you try to do that, the compiler will give an error. The system knows that the purpose of the constructor is to create an object of the class and it will do the same irrespective of whether you declare a return type or not.
Can a constructor be declared as virtual?
A constructor cannot be virtual because at the time when the constructor is invoked the virtual table would not be available in the memory. Hence we cannot have a virtual constructor. ## Constructor called implicitly not explicitly so constructor is not virtual.
Can you overload destructor for your class?
No. Classes can only have one destructor, whether you define one yourself or allow the compiler to generate one for you. The compiler-generated destructor is public by default, does not release any memory allocated to any class' member pointers, and is non-virtual, which are the three main reasons for defining your own.
Why constructor and destructor cannot be made static?
The term "destructor" made me believe this question is related to .Net languages. A destructor is to destroy an instance of object. If it is available at static/class level, what is it going to destroy? The entire class, so the class no longer available? Thus, semantically, destructor should be an instance method. Constructor is on the opposite end of the life cycle of an instance. However, in .NET, a static constructor is allowed. Personally, I call this static constructor as a class initialization method. This method will be invoked by the .net framework only once when the class is loaded into the application domain. With the similar concept, there should be a "finalizer" of the class when the class is unloaded out of the application domain. But wait, does a class ever go out of the application domain once it's loaded? Yes, only at the termination of the application! Currently a class cannot be unloaded explicitly in codes and thus no point to have a static finalizer.
What are virtual constructors or destructors?
If an object (with a non-virtual destructor) is destroyed explicitly by applying the delete operator to a base-class pointer to the object, the base-class destructor function (matching the pointer type) is called on the object. There is a simple solution to this problem
How can you justify the use of constructor and destructor in c plus plus?
Constructors allow class designers to initialise class attributes at the point of instantiation (whenever an object of the class is created). All classes must have at least one constructor other than the copy and move constructors otherwise it would be impossible to instantiate objects of the class. Copy and move constructors are not required but are generated automatically by the compiler unless the class designer explicitly marks them deleted from the class definition. The copy and move constructors allow new instances to be constructed from existing instances. The only difference between the two is that the move constructor transfers ownership of the member attributes, rather than merely copying them. In classes that contain pointers, the compiler-generated copy constructor only copies the pointer (a shallow copy) not what it points at (a deep copy). Thus class designers must provide a copy constructor in order to deep copy any unshared memory resources. Derived class constructors automatically invoke base class constructors, so classes are always constructed from the bottom up. Copy and move constructors automatically invoke their base class copy and move constructors, respectively, however all other constructors automatically invoke their base class default constructors, which may not be the most efficient method of construction. Thus class designers can invoke specific base class constructors through the constructor's own initialisation list (which is also used to initialise member attributes). Constructor bodies do not require any code except in those cases where initialisation is not possible with the initialisation list alone, however this is usually an indication of poor design choices rather than a limitation of the initialisation list. The initialisation list provides the most efficient mechanism for class initialisation. Every class must have one (and only one) destructor. If one is not provided by the class designer, the compiler generates one for you. However, unless the class contains a pointer to unshared memory, there is no need to define your own. Otherwise you must provide a destructor in order to release the memory. The destructor is the last chance to do so before an object of the class falls from scope. Classes that are intended to act as base classes must provide a virtual destructor (that is, the lowest base class must declared the destructor virtual). This ensures that if an object is destroyed polymorphically (via a pointer to one of its base classes), the most-derived destructor is always invoked first. Destruction of hierarchies is always top down. Note that destructors are not virtual by default for the simple reason that not all classes are intended to act as base classes. The containers provided by the Standard Template Library (STL) are a good example of this as none of the containers have virtual destructors -- so they cannot be used as base classes. Note that if any class method is declared virtual, the destructor must also be declared virtual. However, when inheriting from a base class with a virtual destructor, the class destructor is implicitly virtual (as are all virtual functions inherited from base classes) and does not need to be specified, although its good practice to explicitly include it anyway.
How do you write a C plus plus program for destructor?
Class destructors define operations that will be performed whenever an object of the class falls from scope. This usually involves manually releasing any resources allocated to the object. However, by using resource handles or smart pointers, all resources will be released automatically, thus there is no need to define a destructor. The only time we really need to define a destructor is when the class is intended to be used as a polymorphic base class (has one or more virtual methods) but does not inherit a virtual destructor, in which case we must define a virtual destructor. Classes that do define or inherit a virtual destructor cannot be used polymorphically. However, by using resource handles or smart pointers to manage resources, the destructor body can be left empty. The only reason for declaring the destructor at all is simply to declare it virtual because all methods are non-virtual by default -- unless they override a virtual method of the base class (in which case they can simply be declared as overrides). The only time we need to define a non-empty destructor body is when implementing a resource handle or smart pointers, however the standard library already provides efficient implementations so, other than for educational purposes, there is no need to define our own resource handles.
What is the name of the special member function which is automatically called during creation of each class object?
The constructor. The constructor instantiates the object, and can optionally take parameters and has an optional initialization phase. It has no return type, and has the same name as the class itself. The constructor can be overloaded. It cannot be virtual or constant.
When destructor can be virtual in c plus plus?
A class constructor initialises object member variables, ensuring the object is in a valid state from the point of instantiation. The destructor resets those same variables when the object falls from scope. Typically, the destructor is only required to release any memory allocated to any internal class pointers.
Why constructers can not be inherrited in c plus plus?
Every class of object must provide its own specific construction code. Since they are not really functions they cannot be overridden, thus they cannot be inherited. The same applies to the class destructor and the class self-assignment operator. Each class must handle these explicitly, within the class implementation. They cannot be implemented outside of the class, and therefore cannot be inherited. Although the virtual keyword can be applied to the destructor, it's not a function and therefore not a virtual function. The only reason for having a virtual destructor at all is when one or more of the class methods are virtual. Since classes with virtual methods are intended to act as generic interfaces for more specialised implementations, it's important that when destroying such a class that the most-derived (or most-specialised) class is destroyed first, working up the hierarchy to the base class which must always be destroyed last. This can only be achieved through virtual destruction. Failure to declare the base class destructor virtual could result in a base class being destroyed (such as when deleting a pointer to it), which would then result in an incomplete and therefore invalid derived class remaining in memory.
How do you implement inheritance in c plus plus?
You implement inheritance by deriving a new class of object from an existing class of object. The existing class is known as the base class of the derived class.Classes declared final cannot be used as bases classes and classes without a virtual destructor (or a virtual destructor override) cannot be used as polymorphic base classes.
