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. The example below forces all characters to uppercase, and limits the range of characters to A-Z. 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); }