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
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
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
You do get the surprising result that if you have a child, you can’t call foo, but you can cast it to a base and then call foo. child *c = new child(); c->foo; // compile error (can’t access private member) static_cast<base *>(c)->foo(); // this is fine, but still calls the implementation in child I … 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
Hear it from the horse’s mouth. 🙂 From Bjarne Stroustrup’s C++ Style and Technique FAQ Why don’t we have virtual constructors? A virtual call is a mechanism to get work done given partial information. In particular, “virtual” allows us to call a function knowing only any interfaces and not the exact type of the object. … Read more
For the interface, the addition of the abstract, or even the public keywords would be redundant, so you omit them: interface MyInterface { void Method(); } In the CIL, the method is marked virtual and abstract. (Note that Java allows interface members to be declared public abstract). For the implementing class, there are some options: … Read more
From wikipedia In Java, all non-static methods are by default “virtual functions.” Only methods marked with the keyword final, which cannot be overridden, along with private methods, which are not inherited, are non-virtual.
I ran some timings on a 3ghz in-order PowerPC processor. On that architecture, a virtual function call costs 7 nanoseconds longer than a direct (non-virtual) function call. So, not really worth worrying about the cost unless the function is something like a trivial Get()/Set() accessor, in which anything other than inline is kind of wasteful. … 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