PRB: MFC and CRT Must Match in debug/release and static/dynamic

 Last reviewed: July 2, 1997
Article ID: Q166504
The information in this article applies to:
  • The Microsoft Foundation Classes (MFC) included with:
  • Microsoft Visual C++, 32-bit Editions, versions 2.0, 2.1, 2.2, 4.0, 4.1, 4.2, 5.0

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 app 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 apps 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: 

   ARTICLE-ID: Q126646
   TITLE     : PRB: Error Msg: LNK2001 on __beginthreadex and __endthreadex

   ARTICLE-ID: Q128641
   TITLE     : The /Mx Compiler Options and the LIBC, LIBCMT, MSVCRT Libs

Keywords : CRTIss MfcMISC kbbug
Technology : kbMfc
Version : 2.0 2.1 2.2 4.0 4.1 4.2 5.0
Platform : NT WINDOWS
Issue type : kbbug

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Last reviewed: July 2, 1997
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