C++ class forward declaration

Question

When I try to compile this code i get:

52 C:\\Dev-Cpp\\Projektyyy\\strategy\\Tiles.h invalid use of undefined type `struct tile_tree_apple\' 
46 C:\\Dev-Cpp\         


        

Answer 1

Use forward declaration when possible.

Suppose you want to define a new class B that uses objects of class A.

1. B only uses references or pointers to A. Use forward declaration then you don't need to include . This will in turn speed a little bit the compilation.

   class A ;
   
   class B 
   {
     private:
       A* fPtrA ;
     public:
       void mymethod(const& A) const ;
   } ;
   

2. B derives from A or B explicitely (or implicitely) uses objects of class A. You then need to include

   #include 
   
   class B : public A 
   {
   };
   
   class C 
   {
     private:
       A fA ;
     public:
       void mymethod(A par) ;   
   }