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Q165076: INFO: LNK2001 on CRT Symbols in ATL Release Build

Article: Q165076
Product(s): Microsoft C Compiler
Version(s): 2.0,2.1,3.0
Operating System(s): 
Keyword(s): kbATL200 kbATL210 kbCRT kbVC600 kbATL300 kbFAQ kbGrpDSMFCATL
Last Modified: 02-MAY-2002

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The information in this article applies to:

- The Microsoft Active Template Library (ATL), versions 2.0, 2.1, 3.0 
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SUMMARY
=======

Microsoft Active Template Library COM AppWizard generates a release build of
your project using macro _ATL_MIN_CRT. Selecting this configuration causes the C
run-time (CRT) library startup code to not be linked into your project. If you
use functions or code in your project that require the use of the C run-time
library startup code, you may experience LNK2001 - unresolved external errors
when you try to build the release version of your project.

MORE INFORMATION
================

You can use some C run-time functions without requiring the CRT startup code.
Examples include the mem* functions. Other functions require the CRT startup
code. CRT string comparisons for example require the startup code as the CRT
initializes some tables used for comparing. Global objects that have
constructors also require the startup code. In Visual C++ 5.0, statically
linking the startup code adds about 25K to your image (in Visual C++ 4.2 it is
about 20K).

Following are some suggestions for finding the cause of the LNK2001 errors:

- In the linker options there is an "ignore libraries" edit box. Enter
  Libcmt.lib into it, and build. You get several unresolved externals. This
  list is everything that you are using from the CRT. Look for things that you
  think may be pulling in the startup code and remove them if you can.

- Don't ignore Libcmt.lib, but turn on the verbose flag for the linker. From
  this, you can see what is triggering CRT startup code to get pulled in.

If you decide that you really need the startup code, then remove the _ATL_MIN_CRT
define from the project settings. You can also dynamically link to the CRT,
which reduces your image size but requires the CRT's DLL. If you turn on
exception handling you have to pull in the startup code. Even when building
minsize the default is to statically link to the CRT and use _ATL_MIN_CRT.

Additional query words: kbatl200 kbATL210 kbATL300 kbCtrl kbserver kberrmsg c-runtime

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Keywords          : kbATL200 kbATL210 kbCRT kbVC600 kbATL300 kbFAQ kbGrpDSMFCATL 
Technology        : kbVCsearch kbAudDeveloper kbATLsearch kbATL200 kbATL300 kbATL210
Version           : :2.0,2.1,3.0
Issue type        : kbinfo

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