I've found a strange looking piece of code in a project I have to maintain. There's an empty array member of a class which doesn't lead to an compiler error. I've tested some variations of such a code with MSVC 10.0:
template<class T> struct A {
int i[];
}; // warning C4200: nonstandard extension used : zero-sized array in struct/union
template<class T> struct B { static int i[]; };
template<class T> int B<T>::i[];
struct C {
int i[];
}; //warning C4200: nonstandard extension used : zero-sized array in struct/union
template<class T> struct D { static int i[]; };
template<class T> int D<T>::i[4];
template<> int D<int>::i[] = { 1 };
int main()
{
A<void> a;
B<void> b;
C c;
D<void> d0;
D<int> d1;
a.i[0] = 0; // warning C4739: reference to variable 'a' exceeds its storage space
b.i[0] = 0; // warning C4789: destination of memory copy is too small
c.i[0] = 0; // warning C4739: reference to variable 'c' exceeds its storage space
int i[]; // error C2133: 'i' : unknown size
d0.i[0] = 0; // ok
d0.i[1] = 0; // ok
return 0;
}
The error message at int i[] is absolutely sensible to me. The code which is shown with class D is well-formed standard C++. But what's about the classes A, B and C? What kind of types are the member variables int i[] in this classes?