Question

Does constant static member variables of a class or a struct in C++ need not be defined separately?

Is this correct?

struct test
{
    const static int x;
};

int test::x;

Answer 1

No that’s not correct. The definition must match the declaration and x is const int, not int. As a const variable of POD type it also needs to be initialized. E.g.

const int test::x = 0;

As a const static member of integral type, it is also allowed to supply the initializer in the definition of the class instead.