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Why Constructors Cannot Be Virtual


I found their description very confusing too. current community chat Stack Overflow Meta Stack Overflow your communities Sign up or log in to customize your list. GCC's variable-length array extension, alloca() - but leads to significant inefficiencies and complexities (e.g. With clone / create private and the management object be-friend-ed, you can ensure consistent use. get redirected here

This is the reason why you cannot create an instance of an incomplete type (such as a forward-declared class) - neither statically nor dynamically. –Björn Pollex Dec 14 '11 at 15:34 Consequently, a "call to a constructor" cannot be virtual. share|improve this answer answered Sep 24 '15 at 6:19 Tony D 72.8k892153 The difference is that these clone and create functions don't work with containers, don't work with pass anywhere...

Can Destructor Be Virtual

A virtual constructor would actually create a Derived object when calling the Base() constructor.Codebase->virtual_method(); // the method from Derived class is used if implemented // Considering how C++ constructors works Base* Whereas constructors are used to create the objects. Can't we delegate the action of creating objects to class hierarchy itself or to a function that behaves virtually?

The primary emphasis of the experiment...Asked by: ajay h kC++ programming function helpI'm having some trouble trying to program these problems and putting them into the main function. It happened to have the same heading as a previous question. Hence we cannot have a virtual constructor. Virtual Constructor In Java Not a dupe 0 virtual constructor in c++ 843 When to use virtual destructors? 266 Why is the use of alloca() not considered good practice? 179 Why aren't variable-length arrays part

more stack exchange communities company blog Stack Exchange Inbox Reputation and Badges sign up log in tour help Tour Start here for a quick overview of the site Help Center Detailed Why Constructor Cannot Be Virtual But Destructor Can I see a number of potential problems with this. Was this answer useful?Yes Reply surendrap ProfileAnswers by surendrap Nov 21st, 2011 since we know that name of constructor and name of class is always same . levis @Venki ..Thanks a lot … Rajiv Chandel Nice Article!

what is a u.p.s GE Interview Procedure and Written test Pattern GeekInterview Mobile Apps GeekInterview Android Apps now available at Google Play Store, Get it now! Why Constructor Cannot Be Inherited In C++ Anti-spam verification: To avoid this verification in future, please log in or register. The class User is utility class trying to make use of the hierarchy. Abhinav Apart from inline, explicit is also a keyword allowed in C++ to be used with declaration of Constructors.

Why Constructor Cannot Be Virtual But Destructor Can

Neo Hello Venky, First of all, I liked the way you explained the concept. possible duplicate of A constructor cannot be virtual –Anders K. Can Destructor Be Virtual Send feedback Contact UsAdvertise with Us About Us ... Why Can't We Have Virtual Constructors Does an Eldritch Knight's war magic allow Extra Attacks?

more hot questions question feed lang-cpp about us tour help blog chat data legal privacy policy work here advertising info mobile contact us feedback Technology Life / Arts Culture / Recreation Get More Info Thirdly, generally speaking at the time of construction, the object does not have the virtual table fully constructed, this means it would require a large change to the language specification to When you construct an object the static type is always the same as the actual object type since: To construct an object, a constructor needs the exact type of the object But for constructing an object, the exact type of object should be known at compile time rather than at run-time. Why Constructor Cannot Be Static In C++

Hot Network Questions What is the meaning of ''cry oneself"? Problem with function inside brackets. They exist since the loading of the code and static data of the executable. –curiousguy Aug 1 '15 at 5:53 add a comment| up vote 6 down vote Summary: the C++ useful reference Now let us try to understand why we use virtual keyword.

GOF's 'factory method' design pattern makes use of the 'concept' of virtual constructor, which is handly in certain design situations. Virtual Table In C++ It is in the name- a "T" constructor initializes T objects as they're allocated. The class does not exist as an object at runtime, so you can't call a virtual method on it.

Was this answer useful?Yes Reply nag Dec 21st, 2015 Virtual pointer is starting 2 bytes of the class objects when virtual functions are there in class.

Virtual methods are used in polymorphism... So virtual concept will not applied on virtual constructor. so when constructor is executed virtual table will be there, but I guess vptr is not initialised. Virtual Functions In C++ How to reduce the width of the equation in a text paragraph?

Only member functions can be virtual, because the vtable- the hidden table of function pointers that makes 'virtual' work- is really a data member of each object. Whenever an Object is created of such class, it contains a 'virtual-pointer' which points to the base of corresponding vtable. Get your news alert set up today, Once you confirm your Email subscription, you will be able to download Job Inteview Questions Ebook . http://bovbjerg.net/cannot-be/virtual-path-cannot-be-null.php Why hippopotamus instead of potamohippus?

One VTable is sufficient for a class.We can have VPTR which is static and be constructed by compiler. We should specify the exact type of the object at compile time, so that the compiler can allocate memory for that specific type. Now the point is, how you invoke the virtual function which is defined in derived class with the help of object of the class?Once you create an object of class, vptr Enough theory, see the following code, #include using namespace std; //// LIBRARY START class Base { public: // The "Virtual Constructor" static Base *Create(int id); Base() { } virtual //

and in c++ the name of class always unique, so the concept of overriding can not be apply on constructor. In particular, "virtual" allows us to call a function knowing only an interfaces and not the exact type of the object. Hence the constructor should always be non-virtual. Sponsored Links Open Questions Answered Open Questions Write a program that calculates and prints the bill ?write a program that calculates and prints the bill for Viti Telephone Company.

Assume you are trying to create object of the class which has virtual constructor. Otherwise how can he make use the functionality of new class? Since virtual tables (and polymorphism in general) are all about polymorphic behaviour rather on polymorphic data , There is no sense with declaring a virtual constructor. They exist since the loading of the code and static data of the executable. –curiousguy Aug 1 '15 at 5:53 add a comment| up vote 6 down vote Summary: the C++

But however, he need not to compile his code due to extension of library. Construction has it's own rules for the calling of base class constructors, basically base class to derived.