You receive an "error LNK2001: unresolved external symbol ___argc" error message when the MFC library and the CRT library do not match in debug/release or in static/dynamic in Visual C++ (166504)


The information in this article applies to:

  • The Microsoft Foundation Classes (MFC), when used with:
    • Microsoft Visual C++, 32-bit Editions 2.0
    • Microsoft Visual C++, 32-bit Editions 2.1
    • Microsoft Visual C++, 32-bit Editions 2.2
    • Microsoft Visual C++, 32-bit Editions 4.0
    • Microsoft Visual C++, 32-bit Editions 4.1
    • Microsoft Visual C++, 32-bit Enterprise Edition 4.2
    • Microsoft Visual C++, 32-bit Professional Edition 4.2
    • Microsoft Visual C++, 32-bit Enterprise Edition 5.0
    • Microsoft Visual C++, 32-bit Professional Edition 5.0
    • Microsoft Visual C++, 32-bit Enterprise Edition 6.0
    • Microsoft Visual C++, 32-bit Professional Edition 6.0
    • Microsoft Visual C++, 32-bit Learning Edition 6.0
This article was previously published under Q166504

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 more information about CRT options and MFC, click the following article numbers to view the articles in the Microsoft Knowledge Base:

126646 PRB: Error Msg: LNK2001 on __beginthreadex and __endthreadex

Modification Type:MinorLast Reviewed:6/2/2005
Keywords:kbtshoot kberrmsg kbCRT kbprb KB166504 kbAudDeveloper
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