To debug a DLL using Visual C++, you must build a debugging version of the DLL and call it from an application. However, it is not necessary to build the debugging version of the calling application or to build the calling application with Visual C++. For more information about debugging a DLL, see or the following Knowledge Base articles:
"Debugging a Dynamic-Link Library (DLL) in Windows" (Q85221).
"Problems Loading a Debuggee That Uses a DLL" (Q119518).