HOWTO: Declare Classes That Refer to Each Other

• The Microsoft C/C++ Compiler (CL.EXE) included with: - Microsoft Visual C++ for Windows, versions 1.0, 1.5, 1.51, 1.52 - Microsoft Visual C++, 32-bit Edition, versions 1.0, 2.0, 2.1, 2.2,

       4.0, 4.1, 5.0
  

SUMMARY

In C++, you may need to have two classes that contain data members that refer to the other class as in this example:

   class B
   {
    A * x;
   };

   class A
   {
    B * x;
   };

If the two classes are not declared correctly, errors such as the following can occur:

   test1.h(8) : error C2501: 'B' : missing decl-specifiers
   test1.h(8) : error C2143: syntax error : missing ';' before '*'
   test1.h(8) : error C2501: 'x' : missing decl-specifiers

MORE INFORMATION

Sample Code

   /* Compile options needed: none
   */

   //================================
   // test1.h
   //================================

   #ifndef _a_
   #define _a_

   class B;

   class A : public D
   {
    B * x;
   };

   #endif

   //================================
   // test2.h
   //================================

   #ifndef _b_
   #define _b_

   class A;

   class B : public C
   {
    A * y;
   };

   #endif

   //=================================
   // test.cpp
   //=================================

   class C
   {
    int q;
    };

   class D
   {
    int p;
   };

   #include "test1.h"
   #include "test2.h"

   void main(void)
   {
   }