What's the different in gtk_widget_realize , gtk_widget_map ,and gtk_widget_show

["hzeng" <hzeng hf tvia com>]

Hello,
    I just begin to learn gtk. I want to know what happen inside these founctions when they are called.
It seems like that they all do something to create the widget but I can not know what they do clearly.
Thanks for your help!
Hzeng