An application can register a private window class at any time by using the WinRegisterClass function. You must define the window procedure in the application, choose a unique name, and set the window styles for the class. The following code fragment shows how to register the window class name "MyPrivateClass":

    MRESULT EXPENTRY ClientWndProc(HWND hwnd,ULONG msg,MPARAM mp1, MPARAM mp2);

    HAB hab;

    WinRegisterClass(hab,      /* Anchor block handle            */
        "MyPrivateClass",      /* Name of class being registered */
        ClientWndProc,         /* Window procedure for class     */
        CS_SIZEREDRAW |        /* Class style                    */
        CS_HITTEST,            /* Class style                    */
        0);                    /* Extra bytes to reserve         */