FIX: LNK2001 on AfxSocketInit When Using __stdcall Default

The information in this article applies to:

• The Microsoft Foundation Classes (MFC) included with: Microsoft Visual C++, 32-bit Edition, versions 2.1, 2.2

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);

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);

   BOOL __cdecl AfxSocketInit(WSADATA* lpwsaData = NULL);

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

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