Normally each application contains a small main function that does nothing but invoke Tk_Main. Tk_Main then does all the work of creating and running a wish-like application.
When it is has finished its own initialization, but before it processes commands, Tk_Main calls the procedure given by the appInitProc argument. This procedure provides a “hook” for the application to perform its own initialization, such as defining application-specific commands. The procedure must have an interface that matches the type Tcl_AppInitProc:
typedef int Tcl_AppInitProc(
Tcl_Interp *interp);
AppInitProc is almost always a pointer to Tcl_AppInit;
for more details on this procedure, see the documentation
for Tcl_AppInit.
Tk_Main functions much the same as Tcl_Main. In particular, Tk_Main supports both an interactive mode and a startup script mode, with the file name and encoding of a startup script under the control of the Tcl_SetStartupScript and Tcl_GetStartupScript routines. However it calls Tk_MainLoop after processing any supplied script, and in interactive uses events registered with Tcl_CreateFileHandler to process user input.