The compiler must emit a vtable for classes with virtual methods. This contains the pointers to these methods. If all the virtual methods are inline (defined in the header), then the compiler doesn’t know which translation unit (.cpp file) to emit the vtable within, so it emits a copy in all of them and the … Read more
No. static on a function in a class means that the function doesn’t need an object to operate on. virtual means the implementation depends on the type of the calling object. For static there is no calling object, so it doesn’t make sense to have both static and virtual on the same function .
After some thinking I recognized this as the classic multi-method requirement, i.e. a method that dispatches based on the runtime type of more than one parameter. Usual virtual functions are single dispatch in comparison (and they dispatch on the type of this only). Refer to the following: Andrei Alexandrescu has written (the seminal bits for … Read more
Looks like the GCC 5.1 release added exactly the warning I was looking for: -Wsuggest-override Warn about overriding virtual functions that are not marked with the override keyword. Compiling with -Wsuggest-override -Werror=suggest-override would then enforce that all overrides use override.
I am going to go against the flow here… but first, I must assume that your PublicBase destructor is virtual, as otherwise the Derived destructor will never be called. It is usually not a good idea to call a virtual function from a constructor/destructor The reason for this is that dynamic dispatch is strange during … Read more
If a class has a virtual method, that means you want other classes to inherit from it. These classes could be destroyed through a base-class-reference or pointer, but this would only work if the base-class has a virtual destructor. If you have a class that is supposed to be usable polymorphically, it should also be … Read more
If the function were virtual, then you could do this and still get the output “2”: Parent* a = new Child(); a->say(); This works because a virtual function uses the actual type whereas a non-virtual function uses the declared type. Read up on polymorphism for a better discussion of why you’d want to do this.
The problem with this setup is that the operator<< you defined above is a free function, which can’t be virtual (it has no receiver object). In order to make the function virtual, it must be defined as a member of some class, which is problematic here because if you define operator<< as a member of … Read more
The object foo is a local variable with type Foo*. That variable likely gets allocated on the stack for the main function, just like any other local variable. But the value stored in foo is a null pointer. It doesn’t point anywhere. There is no instance of type Foo represented anywhere. To call a virtual … Read more
Is final used for optimization in C++? It can be, and is. As noted, it is being used already; see here and here showing the generated code for the override with and without final. An optimisation along these lines would relate to the “de-virtualization” of the virtual calls. This is not always immediately affected by … Read more