BUG: C2248 When Access Protected Nested Class in Derived Class

• Microsoft C/C++ Compiler (CL.EXE) included with: - Microsoft C/C++ for MS-DOS, version 7.0 - Microsoft Visual C++ for Windows, versions 1.0, 1.5, 1.51 - Microsoft Visual C++, 32-bit Edition, versions 1.0, 2.0, 2.1, 4.0,

       4.1, 4.2, 5.0
  

SYMPTOMS

In the sample code in this article, class C2 is derived from C1, and contains nested class S2, which is derived from nested class S1, declared in class C1. Compiling the sample code results in the following compiler error:

   error C2248: 'S1' : cannot access protected class declared
                       in class 'C1'

RESOLUTION

Declare nested class C1::S1 as public.

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. We are researching this problem and will post new information here in the Microsoft Knowledge Base as it becomes available.

MORE INFORMATION

Referencing nested class S1 inside of the class C2 declaration does not create a problem, but deriving from it does. Also note that you have to include the base class name for the declaration of the derived nested class (C1::S1). That should not be required, but omitting to do so prevents the compiler from recognizing the nested class from the base class as a valid class name.

Sample Code

   /* Compile options needed: none
   */

   class C1
   {
    protected:
      class S1
      {
      };
   };

   class C2 : public C1
   {
      S1 s1;

      class S2 : public C1::S1    // this line generates C2248 error
      {
      };
   };