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Practical Programming in Tcl & Tk, Third Edition
By Brent B. Welch

Table of Contents
Chapter 46.  Writing a Tk Widget in C


Initializing the Extension

The widget is packaged as an extension that you can dynamically load into wish. Example 46-1 shows the Clock_Init procedure. It registers two commands, clock and oclock, which use the string-based and Tcl_Obj interfaces, respectively. It also initializes the stub table, which is described in Chapter 45, and declares a package so that scripts can load the widget with package require.

Example 46-1 The Clock_Init procedure.
int ClockCmd(ClientData clientData,
             Tcl_Interp *interp,
             int argc, char *argv[]);
int ClockObjCmd(ClientData clientData,
             Tcl_Interp *interp,
             int objc, Tcl_Obj *CONST objv[]);
void ClockObjDelete(ClientData clientData);

/*
 * Clock_Init is called when the package is loaded.
 */

int Clock_Init(Tcl_Interp *interp) {
   if (Tcl_InitStubs(interp, "8.1", 0) == NULL) {
      return TCL_ERROR;
   }
   Tcl_CreateCommand(interp, "wclock", ClockCmd,
          (ClientData)NULL, (Tcl_CmdDeleteProc *)NULL);
   Tcl_CreateObjCommand(interp, "oclock", ClockObjCmd,
          (ClientData)NULL, ClockObjDelete);
   Tcl_PkgProvide(interp, "Tkclock", "1.0");
   return TCL_OK;
}

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