How to define a class within another class' private in C++

Question

Is it possible to define a class in another classes private and use it for an array? For instance:

class a
{
    public:
    private:
    class b;
    b myarray[10];

    class b
    {
        public:
        b(int a):a_val (a){}
        private:
        int a_val;
    };
};

Ignoring public, is there anything wrong with my syntax?

Is it also possible to make a member function in A to modify the private values of b. For instance, myarray[0].a_val = 5; If so, is this syntax also correct?

Answer 1

No, your syntax for defining a private nested class is alright. Although some other things are wrong: You need to define b before creating an array to it. The type needs to be complete.

b is not default constructible so you also need to initialize the array in a constructor initializer list, which is actually not possible in C++03. C++11 offers initializer lists to get that functionality.

Just use a std::vector or std::array.

Fixed version of your code:

class a
{
public:
  // ATTN C++11 feature here
  a() : myarray({ 1, 2}) {}
private:
  class b {
  public:
    b(int a) : a_val (a){}
    int a_val;
  };
  b myarray[2];
};
int main ()
{
  a a;
}