FIX: No Error and Constructor Not Called if Prototype Missing

• Microsoft C/C++ Compiler (CL.EXE), used with:
  • Microsoft Visual C++ 32-bit Edition, versions 4.0, 4.1, 4.2

SYMPTOMS

If a class declaration does not contain a default constructor declaration, but there is a definition of a default constructor, no error message is generated and the constructor is never called. The problem can be reproduced by building the sample code below.

RESOLUTION

Make sure that each constructor implementation has its prototype in the class declaration.

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. This bug was corrected in Visual C++ version 5.0.

MORE INFORMATION

Sample Code

   /* Compile options needed: none
   */ 

   #include <iostream.h>

   class MyClass
   {
   public:
      int m_n;
      // No declaration of a default constructor
   };

   MyClass::MyClass() :    // C2600 here.
       m_n (42)
   {
   }

   void main()
   {
       MyClass t;     // Default constructor is not called

       cout << "m_n is " << t.m_n << endl;
       cout << "It should be 42 ";
       cout << "if the correct default constructor was called." << endl;
   } 

error C2600: 'MyClass::MyClass' : cannot define a compiler-generated special member function (must be declared in the class first)

Additional query words: kbVC400bug

Keywords : kbCompiler kbCPPonly kbLangCPP kbVC kbVC500fix
Version : :4.0,4.1,4.2
Platform : NT WINDOWS
Issue type : kbbug