Check that a widget is a child of its Fl_Grid parent

... when assigning it to a cell. This is required for consistency.

1 files changed, 9 insertions, 1 deletions

diff --git a/src/Fl_Grid.cxx b/src/Fl_Grid.cxx
index 66991345d..2952badc3 100644
--- a/src/Fl_Grid.cxx
+++ b/src/Fl_Grid.cxx
@@ -773,6 +773,9 @@ Fl_Grid::Cell *Fl_Grid::widget(Fl_Widget *wi, int row, int col, Fl_Grid_Align al
   assigned to another widget that widget is deassigned but kept as a
   child of the group.
 
+  Before you can assign a widget to a cell it must have been created as
+  a child of the Fl_Grid widget (i.e. its Fl_Group).
+
   \param[in]  wi        widget to be assigned to the cell
   \param[in]  row       row
   \param[in]  col       column
@@ -781,10 +784,15 @@ Fl_Grid::Cell *Fl_Grid::widget(Fl_Widget *wi, int row, int col, Fl_Grid_Align al
   \param[in]  align     widget alignment inside the cell
 
   \return     assigned cell
-  \retval     NULL      if \p row or \p col is out of bounds
+  \retval     NULL      if \p row or \p col is out of bounds or \p wi is not a child
 */
 Fl_Grid::Cell *Fl_Grid::widget(Fl_Widget *wi, int row, int col, int rowspan, int colspan, Fl_Grid_Align align) {
 
+  int child = Fl_Group::find(wi); // is this widget one of our children?
+  if (child >= children()) {
+    // fprintf(stderr, "Fl_Grid::widget(): can't assign widget %p to cell (%d, %d): not a child!\n", wi, row, col);
+    return 0;
+  }
   if (row < 0 || row > rows_)
     return 0;
   if (col < 0 || col > cols_)