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A virtual function is a method defined and implemented in a base class that we are expected to override in our derived classes.
When we derive a class from a base class, we automatically inherit all the public and protected members of the base class, but we are free to override any and all the methods, including private methods (we can even change the access type if we wish).
However, when we override a method in the base class, we can only call that override when we actually have a reference or pointer to the derived class itself. If we cast the reference or pointer to the base class we will end up calling the base class method. This is expected behaviour and is normally fine, but what happens if we have a pointer to a base class but we actually want to call the derived class method? This is particularly important when that call comes from the base class itself. How will it determine its actual type and make the correct call?
We could use runtime information within the base class to determine the actual type, but this would break a fundamental rule of encapsulation: a base class should NEVER be concerned about the inner workings of any of its derived classes. If we allow this, we'd be forced to update the base class every time we derived a new class from it. Apart from the performance penalty incurred with accessing runtime information, maintaining the base class code will quickly become unmanageable.
That is where virtual functions come in. Even though we are pointing at a base class, when we call a virtual function we actually call the derived class method instead. This is extremely powerful: we are no longer concerned with the actual type of object any more. We can treat the base class as if it were a generic data type, and the compiler will know exactly which version of a function to call regardless of whether the call was made from the base class or not.
But what if we want to call the base class method? Simple: make an explicit call to it. We don't need runtime information for this since every derived class is also a base class as well. The only exception is when the virtual function is declared private in the base class. In this case, we are not expected to call the base class method at all (only the base class and friends of the base class can make an explicit call to its private methods).
What else can I help you with?
Constructor cannot be virtual but destructor can be virtual justify?
bcoz constructor cant be invoked
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.
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.
1 Explain the concepts of constructor and destructor Do you have to declare a constructor every time you create a class?
You only need a constructor if the default constructor will not suffice. Often times, it is useful to have a constructor that takes common parameters so that you do not have to write additional code. For example, a Point class might have a constructor for Point(int x, int y), which would be a shortcut for assigning x and y independently. Other classes may not need any default values assigned, and for this, it is acceptable to just use the default constructor. Finally, some classes are virtual, static, or abstract, and so may not need a constructor because the constructor is unnecessary (static), or may be defined elsewhere (virtual, abstract).
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.
Constructor cannot be virtual but destructor can be virtual justify?
bcoz constructor cant be invoked
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.
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.
Why you require constructor in cpp?
Constructors are not a requirement of CPP. A default constructor and copy constructor are automatically generated by the compiler for every class you create when no constructors are declared. The only time you need to declare a constructor is when you wish to override the default behaviour of the generated constructors, to ensure the class is correctly initialised. When any constructor is declared, the default constructor is no longer generated by the compiler -- you must define your own default constructor (one that has no parameters, or where all the parameters have default values). The copy constructor is always generated for you regardless of how many other constructors you declare. But if the class contains pointers to allocated memory that is "owned" by the class then you must override the generated copy constructor with your own copy constructor. This is to ensure the memory is deep copied (the generated copy constructor only performs a shallow, member-wise copy of the members). Otherwise two objects of the same class will end up pointing at the same memory, which would be disastrous if either one were to be deleted. The other instance would be automatically invalidated because it would point to memory that was released by the other instance's destructor.
What is a dynamic constructor?
dynamic constructor is a way to constructing an object based on the run type of some existing object. it basically uses standard virtual functions/polymorphism
1 Explain the concepts of constructor and destructor Do you have to declare a constructor every time you create a class?
You only need a constructor if the default constructor will not suffice. Often times, it is useful to have a constructor that takes common parameters so that you do not have to write additional code. For example, a Point class might have a constructor for Point(int x, int y), which would be a shortcut for assigning x and y independently. Other classes may not need any default values assigned, and for this, it is acceptable to just use the default constructor. Finally, some classes are virtual, static, or abstract, and so may not need a constructor because the constructor is unnecessary (static), or may be defined elsewhere (virtual, abstract).
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.
How do you declare constructor in cpp?
More or less as you would any other function, except there is no return type (not even void) and an initialisation list can be placed between the declaration and the definition that follows it. The initialisation list allows your constructor to call base class constructors besides the default constructor as well as initialise member variables according to the parameters passed to your constructor. The constructor's name must be the name of the class. Note that if you don't declare any constructors, the compiler generates both a default and copy constructor. If any constructor is declared you lose the default constructor unless you declare one yourself. The copy constructor is always present but must be overridden if your class contains pointers to memory allocated to the class itself. If you don't, the compiler generated copy constructor will perform a member-wise copy of the member variables, resulting in a shallow copy of the pointers themselves, rather than a deep copy of the memory they point to. The copy constructor must accept a constant reference to the same class of object.
Are they any free virtual constructor or building programs you can use to design projects like pergolas or pavilions?
Try Google Sketchup.
What do the initials CBF and CPP stand for?
CPP
How constructor is different from normal member function?
A constructor differs from a normal member function in three ways:A constructor never returns a result. The constructor's declaration reflects this by not even declaring the function as "void." The common design hypothesis is that a well-designed constructor cannot fail, other than maybe in an irrecoverable way (such as a fatal running out of memory).A constructor is never called explicitly except with the new operator.Constructors impose further restrictions. For example, they cannot be declared abstract or virtual, and may have visibility requirements. The common design practise is that at least the default constructor is declared public.
When was CPP Group created?
CPP Group was created in 1980.
