gtk+2.0 text problem

["luft" <luftpalen empal com>]

hello. 

at first, my English is so poor, plz understand me : )

i met gtk+ 2.0 15days ago. 
but i do not fully understand about text. 
text in gtk+ 2.0 is so powerful but it's so difficult to understand and hard to find simple example
and references. 

i have some question about text.

when i press space, i want get token from previous space position to here. 
for example :    aaaa bbbbb  
i wanna get string "bbbbb" 
how can i do that? 
code follow

  g_signal_connect (G_OBJECT (mynotepage->txt), "key-press-event",
                         G_CALLBACK (KeyPressAction), NULL);
.....

static GtkTextIter sp;
GtkTextIter end;  
.....
                  buffer = gtk_text_view_get_buffer
                 (GTK_TEXT_VIEW(currentpage->txt));
                 gtk_text_buffer_get_iter_at_mark(
                         buffer, &end,
                         gtk_text_buffer_get_insert(buffer));
                 str = gtk_text_iter_get_text(&sp, &end);
....

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