Q152055: FIX: No Error and Constructor Not Called if Prototype Missing

Article: Q152055
Product(s): Microsoft C Compiler
Version(s): 4.0,4.1,4.2
Operating System(s): 
Keyword(s): kbCompiler kbCPPonly kbLangCPP kbVC kbVC500fix
Last Modified: 04-AUG-2001

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The information in this article applies to:

- Microsoft C/C++ Compiler (CL.EXE), used with:
   - *EDITOR Please do not choose this product*Microsoft Visual C++ 32-bit Edition* use 241, 265, 225, versions 4.0, 4.1, 4.2 
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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;
     }

Visual C++ 5.0 generates the following error when compiling the sample code
above:

  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 
Technology        : kbVCsearch kbAudDeveloper kbCVCComp
Version           : :4.0,4.1,4.2
Issue type        : kbbug
Solution Type     : kbfix

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