DOCUMENT:Q166504  04-AUG-2001  [visualc]
TITLE   :PRB: MFC and CRT Must Match in debug/release and static/dynamic
PRODUCT :Microsoft C Compiler
PROD/VER:winnt:2.0,2.1,2.2,4.0,4.1,4.2,5.0,6.0
OPER/SYS:
KEYWORDS:kbnokeyword kbCRT kbMFC kbVC200 kbVC210 kbVC220 kbVC400 kbVC410 kbVC420 kbVC500 kbVC600

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

 - The Microsoft Foundation Classes (MFC), used with:
    - Microsoft Visual C++, 32-bit Editions, versions 2.0, 2.1, 2.2, 4.0, 4.1 
    - Microsoft Visual C++, 32-bit Enterprise Edition, version 4.2 
    - Microsoft Visual C++, 32-bit Professional Edition, version 4.2 
    - Microsoft Visual C++, 32-bit Enterprise Edition, version 5.0 
    - Microsoft Visual C++, 32-bit Professional Edition, version 5.0 
    - Microsoft Visual C++, 32-bit Enterprise Edition, version 6.0 
    - Microsoft Visual C++, 32-bit Professional Edition, version 6.0 
    - Microsoft Visual C++, 32-bit Learning Edition, version 6.0 
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SYMPTOMS
========

When the MFC and CRT (C Run-Time) libraries do not match in debug/release or in
static/dynamic, you get errors such as the following when linking:

   nafxcwd.lib(appcore.obj) : error LNK2001: unresolved external symbol ___argc

Many other strange problems may erupt during build or runtime: memory corruption,
memory leaks, complaints from the debug C Run-Time libraries during run-time,
and more.

CAUSE
=====

When building an MFC application or DLL, you need to insure that all relevant
libraries are in sync:

 - If you have selected to build an application using MFC in the Shared Library,
   then you must also use the dynamic version of the C Run-Time (MSVCRT.DLL).

 - If you have selected to build a debug MFC application, then you must also use
   the debug version of the C Run-Time. Similarly, release MFC applications must
   use the non-debug version of the C Run-Time.

 - If your debug MFC application uses extension DLLs, every extension DLL must
   be a debug build as well. Again, release apps must match release extension
   DLLs. The type of C Run-Time library is fixed. Extension DLLs and the
   applications which use them must all use MFC in the shared library, which
   requires the dynamic DLL version of the C Run-Time.

 - If you are linking to any static libraries that also link to MFC or the CRT,
   you should ensure that every static library shares the same properties
   (debug/release, CRT-static/dynamic) as the application.

RESOLUTION
==========

To change the type of C Run-Time library used by an application or DLL, go to
the Build/Project settings property sheet and switch to the C/C++ tab. On the
C/C++ page, choose the "Code Generation" category. Change the value of the "Use
run-time library" listbox. Pay careful attention to make this specific for each
configuration; only one configuration, such as "Win32 (80x86) Debug," should be
selected when you change this value.

   Debug, shared library MFC applications - "Debug Multithreaded Dll."

   Release, shared library MFC applications - "Multithread Dll."

   Debug, static library MFC applications - "Debug Multithreaded."

   Release, static library MFC applications - "Multithreaded."

STATUS
======

This behavior is by design.

REFERENCES
==========

For additional information on C Run-Time options and MFC, please see the
following articles in the Microsoft Knowledge Base:

   Q126646 PRB: Error Msg: LNK2001 on __beginthreadex and __endthreadex

   Q128641 The /Mx Compiler Options and the LIBC, LIBCMT, MSVCRT Libs

(c) Microsoft Corporation 1999, All Rights Reserved.
Contributions by Jason Strayer, Microsoft Corporation


Additional query words:

======================================================================
Keywords          : kbnokeyword kbCRT kbMFC kbVC200 kbVC210 kbVC220 kbVC400 kbVC410 kbVC420 kbVC500 kbVC600 kbGrpDSMFCATL 
Technology        : kbAudDeveloper kbMFC
Version           : winnt:2.0,2.1,2.2,4.0,4.1,4.2,5.0,6.0
Issue type        : kbprb

=============================================================================

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