invalid use of non-static data member

Question

For a code like this:

class foo {
  protected:
    int a;
  public:
    class bar {
      public:
        int getA() {return a;}   // ERROR
    };
    foo()
             


        

Answer 1

In C++, nested classes are not connected to any instance of the outer class. If you want bar to access non-static members of foo, then bar needs to have access to an instance of foo. Maybe something like:

class bar {
  public:
    int getA(foo & f ) {return foo.a;}
};

Or maybe

class bar {
  private:
    foo & f;

  public:
    bar(foo & g)
    : f(g)
    {
    }

    int getA() { return f.a; }
};

In any case, you need to explicitly make sure you have access to an instance of foo.