Windows Help defines a series of internal variables that you can use with macros. After you register a DLL function as a Help macro, you can specify the Windows Help internal variables as parameters to that function when the function appears in hot spots or macro footnotes. These variables are always available, and their values change depending on the current state of the Help file. Many DLL routines, as well as some standard Help macros, require the information residing in these variables.
You can use any of the following Windows Help internal variables in DLL functions.
| Variable | Format spec | Description |
| hwndApp | U | Number specifying the handle (a numeric identifier used by Windows) to the main Help window. This variable is guaranteed to be valid only while the DLL function is executing. |
| hwndContext | U | Number specifying the handle of the Help window (either the main Help window or a secondary window) that is active at the time the DLL is called. |
| qchPath | S | String specifying a fully qualified path of the currently open Help file. |
| qError | U | Long pointer to a structure containing information about the most recent Windows Help error. |
| lTopicNo | U | Number specifying the current topic number. This number is relative to the order of topics in the RTF files used to build the Help file. The current topic is the topic displayed in the Help window that is active when the DLL is called. |
| hfs | U | Number specifying the handle (a numeric identifier used by Windows) to the file system for the currently open Help file. |
| coForeground | U | Number specifying the RGB value of the foreground color of the window that is active when the DLL is called. |
| coBackground | U | Number specifying the RGB value of the background color of the window that is active when the DLL is called. |
For more information about Windows Help internal variables in DLL calls, see Chapter 20, “Writing DLLs for Windows Help.”