There is always just one constructor call, and always of the actual, concrete class that you instantiate. It is your responsibility to endow each derived class with a constructor which calls the base classes’ constructors if and as necessary, as you did in B‘s constructor. Update: Sorry for missing your main point! Thanks to ildjarn. … Read more
You cannot use qualified names there. I you write void Function() { … } you are overriding both functions. Herb Sutter shows how it can be solved. Another option is to rename those functions, because apparently they do something different (otherwise i don’t see the problem of overriding both with identical behavior).
It works because the Standard says that’s how it should happen. I did some tests with GCC, and it turns out for virtual functions, GCC stores the virtual table offset of the function in question, in bytes. struct A { virtual void f() { } virtual void g() { } }; int main() { union … Read more
You can’t. Apple can (using the ledger() system call, which is private), but you can’t. I’m not entirely sure whether launchd’s options work or not – certainly if it was still using the code visible in the last open source version (from 10.9.5), it wouldn’t, because it calls setrlimit(), but it’s been substantially rewritten since … Read more
sizeof(A): 8 3 bytes in the array, 1 byte padding, 4 bytes for the vptr (pointer to the vtable) sizeof(B): 12 A subobject: 8, 3 bytes for the extra array, 1 byte padding sizeof(C): 16 This is probably the surprising one for you… A subobject: 8, 3 bytes for the extra array, 1 byte padding, … Read more
For people who think about the same thing and reach this post by googling, consider abstract factory pattern rather than the solutions here. — For you still don’t have an accpted answer about five years later, let me give it a try(again) .. I’ve ever thought about the Curiously Recurring Template Pattern as a workaround, … Read more
The “virtual function table” or “virtual method table” is a list of method pointers that each class has. It contains pointers to the virtual methods in the class. Each instance of a class has a pointer to the table, which is used when you call a virtual method from the instance. This is because a … Read more
Currently there is no standard way of doing this in C++ although the information must be available somewhere. Otherwise, how could the program call the function? However, GCC provides an extension that allows us to retrieve the address of a virtual function: void (A::*mfp)() = &A::func; printf(“address: %p”, (void*)(b->*mfp)); …assuming the member function has the … 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.
First off, a virtual function is not a pointer with 8 bytes. In C++ nothing but sizeof(char) is guaranteed to be any number of bytes. Second, only the first virtual function in a class increases its size (compiler-dependent, but on most – if not all – it’s like this). All subsequent methods do not. Non-virtual … Read more