Validate input to a GtkEntry

insert_text_handler.c

/*!
 * If you want to validate the text that a user enters into a GtkEntry widget
 * you can attach to the "insert_text" signal of the entry, and modify the text
 * within the callback function.\n
 * The example below forces all characters to uppercase, and limits the range of
 * characters to A-Z.\n
 * Note that the entry is cast to an object of type GtkEditable, from which
 * GtkEntry is derived.
 */

#include <ctype.h>
#include <gtk/gtk.h>

void
insert_text_handler
(
  GtkEntry *entry,
  const gchar *text,
  gint length,
  gint *position,
  gpointer data
)
{
  GtkEditable *editable = GTK_EDITABLE (entry);
  int i, count=0;
  gchar *result = g_new (gchar, length);

  for (i=0; i < length; i++)
  {
    if (!isalpha (text[i]))
      continue;
    result[count++] = islower (text[i]) ? toupper (text[i]) : text[i];
  }
  if (count > 0)
  {
    g_signal_handlers_block_by_func
    (
      G_OBJECT (editable),
      G_CALLBACK (insert_text_handler),
      data
    );
    gtk_editable_insert_text
    (
      editable,
      result,
      count,
      position
    );
    g_signal_handlers_unblock_by_func
    (
      G_OBJECT (editable),
      G_CALLBACK (insert_text_handler),
      data
    );
  }
  g_signal_stop_emission_by_name
  (
    G_OBJECT (editable),
    "insert_text"
  );
  g_free (result);
}

int
main 
(
  int argc,
  char *argv[]
)
{
  GtkWidget *window;
  GtkWidget *entry;
  
  gtk_init (&argc, &argv);
  
  /* create a new window */
  window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
  gtk_window_set_title (GTK_WINDOW (window), "GTK Entry");
  g_signal_connect
  (
    G_OBJECT (window),
    "destroy",
    G_CALLBACK (gtk_main_quit),
    NULL
  );
  entry = gtk_entry_new ();
  g_signal_connect
  (
    G_OBJECT(entry),
    "insert_text",
    G_CALLBACK(insert_text_handler),
    NULL
  );
  gtk_container_add (GTK_CONTAINER (window), entry);
  gtk_widget_show (entry);
  gtk_widget_show (window);
  gtk_main ();
  return (0);
}


/* EOF */