Is it possible to declare a friend function as static?

Question

Here is some C++ example code that compiles and works fine:

class A
{
public:
   A() {/* empty */}

private:
   friend void IncrementValue(A &);
   int v         


        

Answer 1

Sure. Read the second line of the error message carefully: the function was declared extern and later static. So all you have to do is declare it static before the friend declaration:

class A;
static void IncrementValue(A&);

class A {
    // class definition, including friend declaration
};

static void IncrementValue(A&) {
    // code here, of course
}