enquiry about labels

[Pierre CHATEL <addicted2 wanadoo fr>]

Hello,
...and sorry for such a silly question but i'm quite new to GTK and C in
general...
I want to use gtk_label_set_text (from gtk 1.2) in a callback function
in order to change a button's label, but it seems i can only use
'constant' strings like "hello world" with this function but no char *
variables.

So the following procedure's not working at all:

/*decrement the value of the label by 1*/
void
on_button_click_event2 (GtkWidget *button, gpointer label)
{
  char *str;
  int i;
  gtk_label_get(label,&str);
  i = atoi(str);
  i--;
  sprintf(str,"%i",i);
  g_print("%s",str);
  gtk_label_set_text(GTK_LABEL(label),str);
  /* no change of the button's label at this point !!*/
}

But gtk_label_set_text(GTK_LABEL(label),"xxx"); is working !!
Is there a way i can achieve that with an other function (or even this
one ?)

Thanks,

Pierre