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Q135336: FIX: LNK2001 on AfxSocketInit When Using __stdcall Default

Article: Q135336
Product(s): Microsoft C Compiler
Version(s): winnt:
Operating System(s): 
Keyword(s): kbMFC kbVC210bug kbVC220bug kbVC400fix kbWinsock kbGrpDSMFCATL kbNoUpdatekbbuglist kbfi
Last Modified: 06-MAY-2001

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

- The Microsoft Foundation Classes (MFC), used with:
   - Microsoft Visual C++ 32-bit Edition, versions 2.1, 2.20 
-------------------------------------------------------------------------------

SYMPTOMS
========

An MFC sockets application that uses a default calling convention of __stdcall
receives the following error:

  <module name>.obj : error LNK2001: unresolved external symbol

  "?AfxSocketInit@@YGHPAUWSAData@@@Z
  (int _stdcall AfxSocketInit(struct WSAData *))"

CAUSE
=====

The AfxSocketInit function is declared in AFXSOCK.H as follows:

     BOOL AfxSocketInit(WSADATA* lpwsaData = NULL);

Note that it has no modifiers on the name of the function. Because of this, the
function calling conventions used by the compiler for this function will be
whatever the command-line setting is.

Because MFC is built with the default __cdecl calling convention, the
AfxSocketInit function has its name decorated according to this convention. If
your application is built with the __stdcall calling convention, then the
function will be decorated according to this convention. Your code is
effectively trying to call a function by a different name than the one that
exists in the MFC library (due to the different name decoration), so the linker
cannot resolve your reference.

RESOLUTION
==========

Because MFC is built with the default calling convention of __cdecl, your
application needs to have the AfxSocketInit declaration specifying this. Modify
the declaration of AfxSocketInit in the header file AFXSOCK.H. This file is
installed by default in the directory: \MSVC20\MFC\INCLUDE

Change the declaration of AfxSocketInit from:

     BOOL AfxSocketInit(WSADATA* lpwsaData = NULL);

To:

     BOOL __cdecl AfxSocketInit(WSADATA* lpwsaData = NULL);

After making the change to this declaration, rebuild the .CPP file in your
project that contains the call to AfxSocketInit. Note that you won't need to
rebuild MFC because the MFC libraries have been built with this function being
marked as __cdecl.

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++, 32- bit
edition, version 4.0.

REFERENCES
==========

For more information on how to track down LNK2001 errors, please use the Help
file.

Additional query words: 2.10 2.20 3.10 3.20 S_MFC

======================================================================
Keywords          : kbMFC kbVC210bug kbVC220bug kbVC400fix kbWinsock kbGrpDSMFCATL kbNoUpdate kbbuglist kbfixlist
Technology        : kbAudDeveloper kbMFC
Version           : winnt:
Issue type        : kbbug
Solution Type     : kbfix

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