The Microsoft Foundation class CWinApp provides much of the framework of a basic Windows application. You will typically not need to change very much of this functionality except for the initialization parts. The following six member functions of CWinApp are designed to be overridden in derived classes. You will almost always override InitInstance. The other functions can be overridden as needed to provide special processing beyond the default behavior.
| CWinApp function | Purpose | When to override |
| InitApplication | One-time application initialization | Seldom |
| InitInstance | Creates main window | Almost always |
| Run | Message loop | Seldom |
| PreTranslateMessage | Extra message processing | Seldom |
| OnIdle | Idle loop processing | If needed to perform background tasks when no messages are pending |
| ExitInstance | Called when program terminates, returns exit code to Windows | Sometimes, to perform application cleanup |