INFO: What Causes the Startup Code to Be Included

• The C Run-time (CRT) included with: - Microsoft C for MS-DOS, versions 6.0, 6.0a, 6.0ax - Microsoft C/C++ for MS-DOS, version 7.0 - Microsoft Visual C++ for Windows, versions 1.0, 1.5 - Microsoft Visual C++ 32-bit Edition, versions 1.0, 2.0, 2.1, 4.0, 5.0

SUMMARY

The object modules created by the Microsoft C Compiler versions 5.1 and earlier contain a reference to the variable _acrtused. This variable causes the linker to bring in the C startup code. To not link the C startup code, it is necessary to define _acrtused as follows:

   int _acrtused = 0;

For 32-bit targets, __acrtused is not used. Instead, the linker must be told what entry point name to use. The Visual C++ for Windows NT linker picks the name based on the executable type. With the Windows Software Development Kit (SDK) linker, the correct entry point must be specified in the makefile or on the command line. The three entry points are:

   Executable Type     Entry Point     Entry Point Name
   ---------------     -----------     ----------------
   Console             main()          _mainCRTStartup
   Windows             WinMain()       _WinMainCRTStartup
   DLL                 DllMain()       _DllMainCRTStartup@12

MORE INFORMATION

With Visual C++ 2.x and above, if a DLL project specifies an entry point and attempts to call a CRT function, the linker issues error LNK2001 because it is looking for main(). To successfully link the DLL, remove the project setting for entry point. As mentioned in the SUMMARY, _DllMainCRTStartup is the correct entry point.