C++ classes using each other

[mirketiger]

I have this code it is not important tah methods have Serbian name it;s not that that's problem :)

 
class cosinus;
 
class sinus : public funkcija
{
private:
  funkcija *_op;
public:
  sinus(funkcija* op1)
   :_op(op1)
  {}
 
  void stampaj() const
  {
   cout << "sin(";
    _op->stampaj();
   cout << ")"; 
  }
  proizvod* izvod() const
  {
    return new proizvod(_op->izvod(),new cosinus(_op));
  }
  double vrednost(double argument) const
  {
    return sin(_op->vrednost(argument));
  }
};
 
class cosinus : public funkcija
{
private:
  funkcija *_op;
public:
  cosinus(funkcija* op1)
   :_op(op1)
  {}
 
  void stampaj() const
  {
   cout << "cos(";
    _op->stampaj();
   cout << ")"; 
  }
  uminus* izvod() const
  {
    return new uminus(new proizvod(_op->izvod(),new sinus(_op)));
  }
  double vrednost(double argument) const
  {
    return cos(_op->vrednost(argument));
  }
 
 
};
 

I get this errors
klase.cpp: In member function 'virtual proizvod* sinus::izvod() const':
klase.cpp:231: error: invalid use of incomplete type 'struct cosinus'
klase.cpp:212: error: forward declaration of 'struct cosinus'


what should I do, to make this work?

[Banfa]

@mirketiger
This error occurs when you try to use a type (class/struct) that you have declared but not defined. That is a type for which the compiler has only seen a forward declaration not and actual definition.

You are getting this because function sinus::izvod is trying to use the type cosinus but at that point there has only been a forward declaration of cosinus.

You need to define sinus::izvod in the presence of the definition of cosinus. The structure you have for your code does not allow this because you have mixed the definitions of the member functions of both sinus and cosinus into the definition of the types sinus and cosinus. You will have to change this so that your code has the following structure:

1. define sinus including declarations (rather than definitions as you have at present) of its member functions.
2. define cosinus including declarations (rather than definitions as you have at present) of its member functions.
3. define member functions of sinus
4. define member functions of cosinus

Note that no forward declarations are required because neither of the classes sinus and cosinus use a pointer to the other one in there definition. Also note that all the member functions of both sinus and cosinus are defined in the presence of definitions of both sinus and cosinus.

This is one of the reasons the standard way to implement a class is using 1 header and 1 source file for the class. The header contains the class definition and source file the member function definitions allowing the inclusion of headers for any other class used.

[mirketiger]

Thanks man. It worked :)