vtable

Does every object of virtual class have a pointer to vtable? Or only the object of base class with virtual function has it? Where did the vtable stored? code section or data section of process? All classes with a virtual method will have a single vtable that is shared by all objects of the class. Each object instance will have a pointer to that vtable (that's how the vtable is found), typically called a vptr. The compiler implicitly generates code to initialize the vptr in the constructor. Note that none of this is mandated by the C++ language - an implementation can handle virtual dispatch

How do the virtual functions work in C# and Java? Does it use same vtable and vpointer concept similar to C++ or is it something totally different? How do virtual functions work in Java? Coding interviewers love this question. Yes. Although Java does NOT have a virtual keyword, Java has virtual functions and you can write them. In object-oriented programming, a virtual function or virtual method is a function or method whose behavior can be overridden within an inheriting class by a function with the same signature. This concept is a very important part of the polymorphism portion of object

This question already has an answer here: Print C++ vtables using GDB 5 answers How to display vtable using a pointer to base class object having virtual functions? Did you try set print object on ? (gdb) help set print object Set printing of object's derived type based on vtable info. If you have a sufficiently new version of gdb, you may want to look at the "info vtbl" command (or perhaps it is called "info vtable"; my own version of gdb is not sufficiently new, and so I cannot test the feature out myself). I only noticed the feature when googling for an answer to this question and I noticed

this is kind of homework question. For the following code, #include <iostream> using namespace std; class A { public: virtual void f(){} }; class B { public: virtual void f2(){} }; class C: public A, public B { public: virtual void f3(){} }; class D: public C { public: virtual void f4(){} }; int main() { cout<<sizeof(D)<<endl; } The output is: 8 Could anyone please explain how it is 8 bytes? If the vtable implementation is compiler dependent, what should I answer for this kind of question in interviews? What about virtual base classes? EDIT: i am working on a 32-bit platform. This is of course

Let say we have below program: class A { public: virtual fun(){}; }; class B:public A { public: virtual fun(){}; }; int main() { A a1; B b1; } My question is how many vtables and how many vptrs will be created, when we run this program? Its heavily implementation dependent, but generally you'll get one vtable object per class that has any virtual functions (classes with no virtual functions or bases don't need them), and one vptr per object of a class with a vtable (pointing at the class's vtable). Things get more complex if you have multiple inheritance and virtual base classes -- which can