Fix return value of Fl_Table_Row::row_selected(int) (PR #1187)

As discussed in the context of PR #1187 the previous return value '-1'
was misleading and undocumented. The docs mentioned only '1' and '0'.

User code that used the return value as documented (like a `bool`)
would make the wrong decision if the return value was '-1': true
(selected) instead false (out of range).

This commit fixes the code by doing what the docs define and clarifies
the documentation.

Further documentation improvements of Fl_Table (example code used a
method that is not defined in Fl_Table) and of Fl_Table_Row are
included as well.

Doxygen docs of two methods of Fl_Table_Row moved to the .cxx file
where they belong according to the CMP.

1 files changed, 33 insertions, 15 deletions

diff --git a/src/Fl_Table_Row.cxx b/src/Fl_Table_Row.cxx
index e800455f8..dca5c10b7 100644
--- a/src/Fl_Table_Row.cxx
+++ b/src/Fl_Table_Row.cxx
@@ -64,10 +64,24 @@ void Fl_Table_Row::CharVector::size(int count) {
 }
 
 
-// Is row selected?
+/**
+  Checks to see if 'row' is selected.
+
+  Returns 1 if selected, 0 if not. You can change the selection of a row
+  by clicking on it, or by using select_row(row, flag)
+
+  \p row \b should be a valid row. If the row is out of range the return
+  value is 0 (zero).
+
+  \param[in] row  row to be checked
+
+  \return whether given row is selected
+  \retval  1  row is selected
+  \retval  0  row is not selected or \p row is out of range
+*/
 int Fl_Table_Row::row_selected(int row) {
-  if ( row < 0 || row >= rows() ) return(-1);
-  return(_rowselect[row]);
+  if (row < 0 || row >= rows()) return 0;
+  return _rowselect[row];
 }
 
 // Change row selection type
@@ -98,18 +112,22 @@ void Fl_Table_Row::type(TableRowSelectMode val) {
   }
 }
 
-// Change selection state for row
-//
-//     flag:
-//        0 - clear selection
-//        1 - set selection
-//        2 - toggle selection
-//
-//     Returns:
-//        0 - selection state did not change
-//        1 - selection state changed
-//       -1 - row out of range or incorrect selection mode
-//
+/**
+  Changes the selection state for \p 'row', depending on the value of \p 'flag'.
+
+  The optional \p flag can be:
+    -  0: clear selection
+    -  1: set selection (default)
+    -  2: toggle selection
+
+  \param[in]  row   row to be selected, deselected, or toggled
+  \param[in]  flag  change mode, see description
+  \return     result of modification, see description
+  \retval   0: selection state did not change
+  \retval   1: selection state changed
+  \retval  -1: row out of range or incorrect selection mode (\p flag)
+*/
+
 int Fl_Table_Row::select_row(int row, int flag) {
   int ret = 0;
   if ( row < 0 || row >= rows() ) { return(-1); }