true_

All this function does it to return true.

This can be useful for example if you want to inhibit the deletion of a window. Of course you should not do this as the user expects a reaction from clicking the close icon of the window...

A persistent window

#include <gtk/gtk.h>

int
main (int argc, char **argv)
{
  GtkWidget *win, *but;
  const char *text = "Close yourself. I mean it!";

  gtk_init (&argc, &argv);

  win = gtk_window_new (GTK_WINDOW_TOPLEVEL);
  g_signal_connect (win,
                    "delete-event",
                    G_CALLBACK (gtk_true),
                    NULL);
  g_signal_connect (win, "destroy",
                    G_CALLBACK (gtk_main_quit),
                    NULL);

  but = gtk_button_new_with_label (text);
  g_signal_connect_swapped (but, "clicked",
                            G_CALLBACK (gtk_object_destroy),
                            win);
  gtk_container_add (GTK_CONTAINER (win), but);

  gtk_widget_show_all (win);

  gtk_main ();

  return 0;
}