Question

I believe the code doesn’t compile, because I’m using the extern const int j to initialize i in class A. But according to the Standard, why is this wrong ?

File A.h

extern const int j;

class A
{
    static const int i = j;     //  error C2057:expected constant expression
};

File A.cpp

#include "A.h"

const int j = 10;

int main()
{
    A a;
}

Answer 1

j is a constant variable, not a compile-time constant.

The compiler can’t know the value of j in the translation unit that compiles class A. For example, the following would work:

static const int j = 10;

class A
{
    static const int i = j;
};

Note that in this case j will not be global, but a copy will exist for each TU. The snippet is here just to prove a point.