static const in c++ class: undefined reference

Question

I have a class for local use only (i.e., its cope is only the c++ file it is defined in)

class A {
public:
    static const int MY_CONST = 5;
};

void fun( int b ) {
    int j = A::MY_CONST;  // no problem
    int k = std::min<int>( A::MY_CONST, b ); // link error: 
                                            // undefined reference to `A::MY_CONST` 
}

All the code reside in the same c++ file. When compiling using VS on windows, there is no problem at all.
However, when compiling on Linux I get the undefined reference error only for the second statement.

Any suggestions?

Answer 1

std::min<int>'s arguments are both const int&(not just int), i.e. references to int. And you can't pass a reference to A::MY_CONST because it is not defined (only declared).

Provide a definition in the .cpp file, outside the class:

class A {
public:
    static const int MY_CONST = 5; // declaration
};

const int A::MY_CONST; // definition (no value needed)