INFO: LNK2001 on CRT Symbols in ATL Release Build

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.

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.