Q149784: FIX: LNK2001 Incorrectly Generated for Static Data Member

Article: Q149784
Product(s): Microsoft C Compiler
Version(s): 4.00
Operating System(s): 
Keyword(s): kbCompiler kbCPPonly kbVCkbbuglist kbfixlist
Last Modified: 30-JUL-2001

-------------------------------------------------------------------------------
The information in this article applies to:

- The C/C++ Compiler (CL.EXE), included with:
   - Microsoft Visual C++, 32-bit Editions, version 4.0 
-------------------------------------------------------------------------------

SYMPTOMS
========

When declaring static members of C++ classes, you must initialize the static
data member. Otherwise the linker generates an unresolved external error
message. Visual C++ 4.0 incorrectly generates such an unresolved external error
message if a storage-class specifier (such as __declspec(X)) is used on the
initialization line of a static data member.

CAUSE
=====

Storage-class specifiers, such as __declspec(), are only necessary for
declarations. They are not needed (but are not wrong) otherwise.

RESOLUTION
==========

Remove the storage-class specifier.

STATUS
======

Microsoft has confirmed this to be a bug in the Microsoft products listed at the
beginning of this article. This problem has been corrected in Microsoft Visual
C++ version 4.1.

MORE INFORMATION
================

Earlier versions of Visual C++ generated the following error when a storage-
class specifier is used on the initialization line:

  

  C:test.cpp('line') : error C2720: 'idata' : '' storage-class specifier
                illegal on members

where 'line' is the line of code where the initialization takes place, and
'idata' is the name of the static data member. Visual C++ no longer generates
the C2720 error (correctly so). The following sample code demonstrates the
problem.

Sample Code
-----------

  /* Compile options needed: none
  */ 

  #include <iostream.h>
  #include <stdio.h>

  class A
  {
    public:
      static __declspec(thread) int idata;
      void test(void);
  };
  __declspec(thread) int  A::idata = 2;  // remove this __declspec(thread) to
                                         // eliminate unresolved external
  error

  void A::test(void)
  {
    cout<<idata;
  }
  void main(void)
  {
    A theA;
    theA.test();
  }

Additional query words: 4.00 lnk2001 lnk1120 L2029 unresolved external LINK

======================================================================
Keywords          : kbCompiler kbCPPonly kbVC kbbuglist kbfixlist
Technology        : kbVCsearch kbAudDeveloper kbCVCComp
Version           : 4.00
Issue type        : kbbug
Solution Type     : kbfix

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