[in]Indicates why the DLL entry-point function is being called. This parameter can be one of the following values: DLL_PROCESS_ATTACH, DLL_THREAD_ATTACH, DLL_THREAD_ATTACH, or DLL_PROCESS_DETACH. For descriptions of these values, see the DllMain documentation in the Platform SDK.
In Windows 98, Windows ME, Windows NT, and Windows 2000, the function is called indirectly through a fixup in the loader. In all other versions of Windows, it is called directly by the operating system loader.