Contents
Where is the virtual table located?
In VC++, the vtable pointer stored at the beginning of the object allocation, before any member data. (Provided your class has at least one virtual member function.)
How virtual function is stored?
The object of the class containing the virtual function contains a virtual pointer that points to the base address of the virtual table in memory. Whenever there is a virtual function call, the v-table is used to resolve to the function address.
What is virtual table and virtual pointer?
Virtual table – A table created at compile time for every single class containing the most derived versions of virtual functions only. Virtual pointer – A data member silently inserted by compiler into the class specification and initialized to virtual table from within constructor.
Which is true about virtual tables?
The virtual table is actually quite simple, though it’s a little complex to describe in words. A virtual table contains one entry for each virtual function that can be called by objects of the class. Each entry in this table is simply a function pointer that points to the most-derived function accessible by that class.
How many virtual tables are created?
Because there are 3 classes here, the compiler will set up 3 virtual tables: one for Base, one for D1, and one for D2.
How do virtual methods work?
A virtual function is a member function that you expect to be redefined in derived classes. When you refer to a derived class object using a pointer or a reference to the base class, you can call a virtual function for that object and execute the derived class’s version of the function.
Which is true about virtual table?
What is purpose of virtual destructor?
A virtual destructor is used to free up the memory space allocated by the derived class object or instance while deleting instances of the derived class using a base class pointer object.
What is pure virtual function?
A pure virtual function or pure virtual method is a virtual function that is required to be implemented by a derived class if the derived class is not abstract. Classes containing pure virtual methods are termed “abstract” and they cannot be instantiated directly.
Where are the pointers in the vtable table?
Each row of the vtable is a function pointer pointing to a corresponding virtual function. To accomplish late binding, the compiler creates this vtable table for each class that contains virtual functions and for the class derived from it. The compiler places the addresses of the virtual functions for that particular class in ‘vtable’.
What happens when you call a virtual pointer?
When virtual function call is made through a base-class pointer, the compiler quietly inserts code to fetch the VPTR and look up the function address in the VTABLE, thus calling the right function and causing late/dynamic binding to take place.
When to add hidden pointer to virtual table?
Second, the compiler also adds a hidden pointer to the base class, which we will call *__vptr. *__vptr is set (automatically) when a class instance is created so that it points to the virtual table for that class.
How does the virtual table work in C + +?
The virtual table is actually quite simple, though it’s a little complex to describe in words. First, every class that uses virtual functions (or is derived from a class that uses virtual functions) is given its own virtual table. This table is simply a static array that the compiler sets up at compile time.