The drawbacks are that All classes will have to initialize all its virtual bases all the time (e.g. if A is virtual base of B, and C derives from B, it also have to initialize A itself). You have to use more expensive dynamic_cast everywhere you use a static_cast (may or may not be the … Read more
There may be, yes, if you call the member function via a pointer or reference and the compiler can’t determine with absolute certainty what type of object that pointer or reference points or refers to. For example, consider: void f(B* p) { p->foo(); } void g() { D bar; f(&bar); } Assuming the call to … Read more
The page “Notes on Multiple Inheritance in GCC C++ Compiler v4.0.1” is offline now, and http://web.archive.org didn’t archive it. So, I have found a copy of the text at tinydrblog which is archived at the web archive. There is full text of the original Notes, published online as part of “Doctoral Programming Language Seminar: GCC … Read more
Everything is absolutely valid. A compiler is allowed to warn about valid code, no problem here. You can try silencing the warning with a using declaration. If this doesn’t work (probably due to an MSVC bug), silence it with a pragma.
[*] The technical problem is that there’s no way to work out from a Base* what the offset is between the start of the Base sub-object and the start of the Derived object. In your example it appears OK, because there’s only one class in sight with a Base base, and so it appears irrelevant … Read more
In order to understand the cast system, you need to dive into the object model. The classic representation of a simple hierarchy model is containment: if B derives from A then the B object will, in fact, contain an A subobject alongside its own attributes. With this model downcasting is a simple pointer manipulation by … Read more
When using virtual inheritance, the virtual base class’s constructor is called directly by the most derived class’s constructor. In this case, the daughter constructor directly calls the grandmother constructor. Since you didn’t explicitly call grandmother constructor in the initialization list, the default constructor will be called. To call the correct constructor, change it to: daugther(int … Read more
You want: (Achievable with virtual inheritance) A / \ B C \ / D And not: (What happens without virtual inheritance) A A | | B C \ / D Virtual inheritance means that there will be only 1 instance of the base A class not 2. Your type D would have 2 vtable pointers … Read more
Virtual base classes, used in virtual inheritance, is a way of preventing multiple “instances” of a given class appearing in an inheritance hierarchy when using multiple inheritance. Consider the following scenario: class A { public: void Foo() {} }; class B : public A {}; class C : public A {}; class D : public … Read more