virtual-inheritance

I was recently asked in an interview about object layout with virtual functions and multiple inheritance involved. I explained it in context of how it is implemented without multiple inheritance involved (i.e. how the compiler generated the virtual table, insert a secret pointer to the virtual table in each object and so on). It seemed to me that there was something missing in my explanation. So here are questions (see example below) What is the exact memory layout of the object of class C. Virtual tables entries for class C. Sizes (as returned by sizeof) of object of classes A, B and C. (8, 8

EDIT3: Please be sure to clearly understand what I am asking before answering (there are EDIT2 and lots of comments around). There are (or were) many answers which clearly show misunderstanding of the question (I know that's also my fault, sorry for that) Hi, I've looked over the questions on virtual inheritance ( class B: public virtual A {...} ) in C++, but did not find an answer to my question. I know that there are some issues with virtual inheritance, but what I'd like to know is in which cases virtual inheritance would be considered a good design. I saw people mentioning interfaces like

Recently ran across a C++ linker error that was new to me. libfoo.so: undefined reference to `VTT for Foo' libfoo.so: undefined reference to `vtable for Foo' I recognized the error and fixed my problem, but I still have a nagging question: what exactly is a VTT? Aside: For those interested, the problem occurs when you forget to define the first virtual function declared in a class. The vtable goes into the compilation unit of the class's first virtual function. If you forget to define that function, you get a linker error that it can't find the vtable rather than the much more developer

class A { int i; public: A() {cout<<"in A's def const\n";}; A(int k) {cout<<"In A const\n"; i = k; } }; class B : virtual public A { public: B(){cout<<"in B's def const\n";}; B(int i) : A(i) {cout<<"in B const\n";} }; class C : public B { public: C() {cout<<"in C def cstr\n";} C(int i) : B(i) {cout<<"in C const\n";} }; int main() { C c(2); return 0; } The output in this case is in A's def const in B const in C const Why is this not entering into in A const `It should follow the order of 1 arg constructor call. But what actually is happening on deriving B from A using virtual keyword. There are

Consider following hierarchy: struct A { int a; A() { f(0); } A(int i) { f(i); } virtual void f(int i) { cout << i; } }; struct B1 : virtual A { int b1; B1(int i) : A(i) { f(i); } virtual void f(int i) { cout << i+10; } }; struct B2 : virtual A { int b2; B2(int i) : A(i) { f(i); } virtual void f(int i) { cout << i+20; } }; struct C : B1, virtual B2 { int c; C() : B1(6),B2(3),A(1){} virtual void f(int i) { cout << i+30; } }; What's the exact memory layout of C instance? How many vptrs it contains, where exactly each of them is placed? Which of virtual tables are shared with virtual table of C?