how to get one character from GtkTextView widget

[gepolv <sssssiqn gmail com>]

I connect signal "insert-text" with funciton "deal_insert" ,and then i want
to get  one character every time from the GtkTextView widget
in funciton "deal_insert".
how can i do it?

the source code:
GtkWidget *text_view;
text_view = gtk_text_view_new ();
GtkTextBuffer *mainbuffer;
    mainbuffer=gtk_text_view_get_buffer (GTK_TEXT_VIEW (text_view));
    g_signal_connect (G_OBJECT (mainbuffer), "insert-text",
                    G_CALLBACK (deal_insert), &mainbuffer);

Thanking .....who