我不明白这个结果

Question

This code doesn't compile in clang

#include <iostream>

namespace M {
    class B {
        public:static const int i = 1000;
    };
}

namespace N {
    class Y /*: public M::B*/ {

        class X {
            int a[i];
            static const int i = 1;

        public:
            X() { for(int j = 0; j < i; ++j ) a[j] = 1; }
            static int Get() { return i; }
        };
        public:
        int Get() { return X::Get(); }
    };
}



int main()
{
    N::Y y;
    std::cout << y.Get() << '\n';
}

But if I comment out /*: public M::B*/ it does, printing 1. However, if I place the statement static const int i = 1; before int a[i]; it compiles on both versions of the code, printing 1.

Would very much appreciate quotes from the Standard.

Answer 1

In the original code with the commented base class you are trying to use name i that was not yet defined

   class X {
        int a[i]; // here i is undefined
        static const int i = 1;

If you will exchange the two definitions

   class X {
        static const int i = 1;
        int a[i];

then the code will be compiled successfuly because i used in the array definition was previously defined..

When base class is uncommented then in this definition

        int a[i];

i is the static data member of class B that is the array is defined as

        int a[1000];

After that you defined static data member i of class X that hides static data member of base class B of class Y inside class X.