Mixing Tcl/Tk and Xt Event Loops

See also: Adding Tk to an Existing Xt Program

George Peter Staplin: The code that follows creates an Xt button and a Tk button, in the same application.

Alas, as time goes on some code doesn't age as well. A better solution is mentioned in the Tk Usage FAQ here:

  #include <stdio.h>
  #include <stdlib.h>
  #include <X11/Intrinsic.h> 
  #include <X11/StringDefs.h> 
  #include <X11/Xaw/Command.h>  
  #include <tcl.h>
  #include <tk.h>

  Tcl_Interp *interp;

  void Action (Widget w, XtPointer client_data, XtPointer call_data) { 
  fprintf (stderr, "You pressed me.\n");
  exit (0); 

  int main (int argc, char *argv) {
  XtAppContext appContext;
  Widget win, button;
  XEvent event;
  int i = 1;

        char sAppInit = "pack button .b -text \"Hello\"";

        win = XtVaAppInitialize(

        button = XtVaCreateManagedWidget (

  interp = Tcl_CreateInterp ();

  Tcl_FindExecutable (argv0); /* Does Tcl_FindExecutable behave better *before* Tcl_CreateInterp()? */

        if (Tcl_Init (interp) != TCL_OK) {
            fprintf (stderr, "Tcl_Init error"); 
            exit (1);

        if (Tk_Init (interp) != TCL_OK) {
            fprintf (stderr, "Tk_Init error");
            exit (1);


  XtAddCallback (button, XtNcallback, Action, 0);
  XtRealizeWidget (win);

        if (Tcl_Eval (interp, sAppInit) != TCL_OK) {
        fprintf (stderr, "Tcl_Eval error %s", Tcl_GetStringResult (interp));

        for (;;) {

                if (XtAppPending (appContext) > 0) {
                XtAppNextEvent (appContext, &event);
                XtDispatchEvent (&event);       nt);
                } else {
                Tcl_DoOneEvent (TCL_DONT_WAIT);
                usleep (200);


  return (0);

Here's a package that contains a Makefile and the code above: http://www.xmission.com/~georgeps/TclTkXt.tgz You may need to change the Makefile string -ltcl83 to -ltcl8.3 and Linux users need to add -ldl.

Have fun!

During summer 2002, GPS mentioned http://www.xmission.com/~georgeps/TclTk_With_GTK-8.tgz and http://www.xmission.com/~georgeps/TclTk_With_Xt-7.tgz as two examples of mixing Tcl/Tk and GTk and Xt.

"Event-oriented programming" has background information.