Is there something wrong with this approach? Answer from Bjarne Stroustrup: Can I call a virtual function from a constructor? Yes, but be careful. It may not do what you expect. In a constructor, the virtual call mechanism is disabled because overriding from derived classes hasn’t yet happened. Objects are constructed from the base up, … Read more
I found one mechanism, where at least we are prompted to announce the overridden method explicitly. It’s not the perfect way though. Suppose, we have few pure virtual methods in the base class B: class B { virtual void foo () = 0; virtual void bar (int) = 0; }; Among them, suppose we want … Read more
Overriding essentially means that either the Base class method or the Derived class method will be called at run-time depending on the actual object pointed by the pointer. It implies that: i.e: Every place where the Base class method can be called can be replaced by call to Derived class method without any change to … Read more
What is function hiding? … is a form of name hiding. A simple example: void foo(int); namespace X { void foo(); void bar() { foo(42); // will not find `::foo` // because `X::foo` hides it } } This also applies to the name lookup in a base class: class Base { public: void foo(int); }; … Read more
This is all implementation defined. I’m using VC10 Beta2. The key to help understanding this stuff (the implementation of virtual functions), you need to know about a secret switch in the Visual Studio compiler, /d1reportSingleClassLayoutXXX. I’ll get to that in a second. The basic rule is the vtable needs to be located at offset 0 … Read more
Those are the offset-to-top (needed for multiple inheritence) and typeinfo (RTTI) pointers. From the Itanium ABI (you are not using the Itanium compiler, but their description of this is really good): The offset to top holds the displacement to the top of the object from the location within the object of the virtual table pointer … Read more
Classes should be designed for inheritance to be able to take advantage of it. Having methods virtual by default means that every function in the class can be plugged out and replaced by another, which is not really a good thing. Many people even believe that classes should have been sealed by default. virtual methods … Read more
They can result if you try to make a virtual function call from a constructor or destructor. Since you can’t make a virtual function call from a constructor or destructor (the derived class object hasn’t been constructed or has already been destroyed), it calls the base class version, which in the case of a pure … Read more
That’s indeed the idea. The point is that you are explicit about what you mean, so that an otherwise silent error can be diagnosed: struct Base { virtual int foo() const; }; struct Derived : Base { virtual int foo() // whoops! { // … } }; The above code compiles, but is not what … Read more