10.1. Labels

Labels are used a lot in GTK, and are relatively simple. Labels emit no signals as they do not have an associated X window. If you need to catch signals, or do clipping, place it inside a EventBox widget or a Button widget.

To create a new label, use:

GtkWidget *gtk_label_new( const char *str );

GtkWidget *gtk_label_new_with_mnemonic( const char *str );

The sole argument is the string you wish the label to display.

To change the label's text after creation, use the function:

void gtk_label_set_text( GtkLabel   *label,
                         const char *str );

The first argument is the label you created previously (cast using the GTK_LABEL() macro), and the second is the new string.

The space needed for the new string will be automatically adjusted if needed. You can produce multi-line labels by putting line breaks in the label string.

To retrieve the current string, use:

const gchar* gtk_label_get_text( GtkLabel  *label );                    

Do not free the returned string, as it is used internally by GTK.

The label text can be justified using:

void gtk_label_set_justify( GtkLabel         *label,
                            GtkJustification  jtype );

Values for jtype are:

  GTK_JUSTIFY_LEFT
  GTK_JUSTIFY_RIGHT
  GTK_JUSTIFY_CENTER (the default)
  GTK_JUSTIFY_FILL

The label widget is also capable of line wrapping the text automatically. This can be activated using:

void gtk_label_set_line_wrap (GtkLabel *label,
                              gboolean  wrap);

The wrap argument takes a TRUE or FALSE value.

If you want your label underlined, then you can set a pattern on the label:

void       gtk_label_set_pattern   (GtkLabel          *label,
                                    const gchar       *pattern);

The pattern argument indicates how the underlining should look. It consists of a string of underscore and space characters. An underscore indicates that the corresponding character in the label should be underlined. For example, the string "__ __" would underline the first two characters and eight and ninth characters.

If you simply want to have an underlined accelerator ("mnemonic") in your label, you should use gtk_label_new_with_mnemonic() or gtk_label_set_text_with_mnemonic(), not gtk_label_set_pattern().

Below is a short example to illustrate these functions. This example makes use of the Frame widget to better demonstrate the label styles. You can ignore this for now as the Frame widget is explained later on.

In GTK+ 2.0, label texts can contain markup for font and other text attribute changes, and labels may be selectable (for copy-and-paste). These advanced features won't be explained here.

#include <gtk/gtk.h>

int main( int   argc,
          char *argv[] )
{
  static GtkWidget *window = NULL;
  GtkWidget *hbox;
  GtkWidget *vbox;
  GtkWidget *frame;
  GtkWidget *label;

  /* Initialise GTK */
  gtk_init (&argc, &argv);

  window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
  g_signal_connect (G_OBJECT (window), "destroy",
		    G_CALLBACK (gtk_main_quit),
		    NULL);

  gtk_window_set_title (GTK_WINDOW (window), "Label");
  vbox = gtk_vbox_new (FALSE, 5);
  hbox = gtk_hbox_new (FALSE, 5);
  gtk_container_add (GTK_CONTAINER (window), hbox);
  gtk_box_pack_start (GTK_BOX (hbox), vbox, FALSE, FALSE, 0);
  gtk_container_set_border_width (GTK_CONTAINER (window), 5);
  
  frame = gtk_frame_new ("Normal Label");
  label = gtk_label_new ("This is a Normal label");
  gtk_container_add (GTK_CONTAINER (frame), label);
  gtk_box_pack_start (GTK_BOX (vbox), frame, FALSE, FALSE, 0);
  
  frame = gtk_frame_new ("Multi-line Label");
  label = gtk_label_new ("This is a Multi-line label.\nSecond line\n" \
			 "Third line");
  gtk_container_add (GTK_CONTAINER (frame), label);
  gtk_box_pack_start (GTK_BOX (vbox), frame, FALSE, FALSE, 0);
  
  frame = gtk_frame_new ("Left Justified Label");
  label = gtk_label_new ("This is a Left-Justified\n" \
			 "Multi-line label.\nThird      line");
  gtk_label_set_justify (GTK_LABEL (label), GTK_JUSTIFY_LEFT);
  gtk_container_add (GTK_CONTAINER (frame), label);
  gtk_box_pack_start (GTK_BOX (vbox), frame, FALSE, FALSE, 0);
  
  frame = gtk_frame_new ("Right Justified Label");
  label = gtk_label_new ("This is a Right-Justified\nMulti-line label.\n" \
			 "Fourth line, (j/k)");
  gtk_label_set_justify (GTK_LABEL (label), GTK_JUSTIFY_RIGHT);
  gtk_container_add (GTK_CONTAINER (frame), label);
  gtk_box_pack_start (GTK_BOX (vbox), frame, FALSE, FALSE, 0);

  vbox = gtk_vbox_new (FALSE, 5);
  gtk_box_pack_start (GTK_BOX (hbox), vbox, FALSE, FALSE, 0);
  frame = gtk_frame_new ("Line wrapped label");
  label = gtk_label_new ("This is an example of a line-wrapped label.  It " \
			 "should not be taking up the entire             " /* big space to test spacing */\
			 "width allocated to it, but automatically " \
			 "wraps the words to fit.  " \
			 "The time has come, for all good men, to come to " \
			 "the aid of their party.  " \
			 "The sixth sheik's six sheep's sick.\n" \
			 "     It supports multiple paragraphs correctly, " \
			 "and  correctly   adds "\
			 "many          extra  spaces. ");
  gtk_label_set_line_wrap (GTK_LABEL (label), TRUE);
  gtk_container_add (GTK_CONTAINER (frame), label);
  gtk_box_pack_start (GTK_BOX (vbox), frame, FALSE, FALSE, 0);
  
  frame = gtk_frame_new ("Filled, wrapped label");
  label = gtk_label_new ("This is an example of a line-wrapped, filled label.  " \
			 "It should be taking "\
			 "up the entire              width allocated to it.  " \
			 "Here is a sentence to prove "\
			 "my point.  Here is another sentence. "\
			 "Here comes the sun, do de do de do.\n"\
			 "    This is a new paragraph.\n"\
			 "    This is another newer, longer, better " \
			 "paragraph.  It is coming to an end, "\
			 "unfortunately.");
  gtk_label_set_justify (GTK_LABEL (label), GTK_JUSTIFY_FILL);
  gtk_label_set_line_wrap (GTK_LABEL (label), TRUE);
  gtk_container_add (GTK_CONTAINER (frame), label);
  gtk_box_pack_start (GTK_BOX (vbox), frame, FALSE, FALSE, 0);
  
  frame = gtk_frame_new ("Underlined label");
  label = gtk_label_new ("This label is underlined!\n"
			 "This one is underlined in quite a funky fashion");
  gtk_label_set_justify (GTK_LABEL (label), GTK_JUSTIFY_LEFT);
  gtk_label_set_pattern (GTK_LABEL (label),
			 "_________________________ _ _________ _ ______     __ _______ ___");
  gtk_container_add (GTK_CONTAINER (frame), label);
  gtk_box_pack_start (GTK_BOX (vbox), frame, FALSE, FALSE, 0);
  
  gtk_widget_show_all (window);

  gtk_main ();
  
  return 0;
}