Question about gtk_label_set_justify()

["chao yeaj" <yeajchao gmail com>]

Hello everyone

    You knowe ,there is a function called
gtk_label_set_justify(),which used to modify the label's text'sjustify
mode

     my code as follow
  GtkWidget *label = NULL;
  gtk_label_new(" I am label!");
  gtk_label_set_justify(GTK_LABEL(label),GTK_JUSTIFY_FILL);

   but ,this do not  work,  Why ?
  I need your help
Any comments would be much appreciated,and thanks in advance !