The number of lines used is updated in the header when a value is set,

and the iteration on the values of a column is done on the number of
lines used (instead of on the total line count).

src/obidmscolumn_int.c

@@ -30,7 +30,9 @@
 
 int obi_column_set_int_with_elt_idx(OBIDMS_column_p column, size_t line_nb, size_t element_idx, obiint_t value)
 {
-	// when/where check if can write?
+	// Update lines used
+	if ((line_nb+1) > (column->header)->lines_used)
+		(column->header)->lines_used = line_nb+1;
 	*(((obiint_t*) (column->data)) + (line_nb * ((column->header)->nb_elements_per_line)) + element_idx) = value;
 	return 0;
 }