bug in use of shallow copy

[Dan Perl]

I found something that seems to me to be a bug, unless I misunderstand
the use of some classes.  Note: we are using version 3.5.1 (according to
the CHANGES file in the top directory).

 

MibTable::getRows( ) makes a shallow copy of the rows in MibTable.  It
creates a "new List<MibTableRow>" and it adds one-by-one one
"MibTableRow *" to the list, for every row in the table.  However, the
destructor ~List( ) invokes List::clearAll( ) which in turn deletes also
the items in the list (the pointers added to list).  Here is the code
from ~List( ):

            void clearAll() {

                        ListItem<T>* tmp = head;

                        ListItem<T>* del;

                        while (tmp) {

                                    delete tmp->item;

                                    del = tmp;

                                    tmp = tmp->next;

                                    delete del;

                        }

                        head = 0;

                        tail = 0;

            }

This is causing a segmentation fault in my code.  I commented out the
"delete tmp->item" line, I ran my code through Purify, and my problem is
solved, and there are no memory leaks.

 

I'm not sure whether there are some other uses of List where the items
should be indeed deleted in thedestructor, but it looks to me like this
is a clear problem for my case.  Am I supposed to access the rows of a
table using some other API methods?  I need to traverse the rows,
searching for a row with a specific value in one of the columns.  Here
is what my code looks like:

  List<MibTableRow>* tableRows = tablePtr->get_rows( );

  ListCursor<MibTableRow> tableRowsCursor;

  MibTableRow* rowPtr = 0;

  for(tableRowsCursor.init(tableRows);

      rowPtr = tableRowsCursor.get();

      tableRowsCursor.next())

  {

     // check if rowPtr is the row we are looking for and if so, break
out of the for loop

  }

  delete tableRows;

  return rowPtr;

 

Note: I have to delete tableRows, or else it is a memory leak.  However,
I do need the rowPtr after that as a pointer INSIDE the actual table.
So I do need MibTable::getRows to make a shallow copy but it should not
destroy the copied items.  Of course, that's so unless I am misusing the
API and there is another way to do what I need.

 

I changed the agent++ code for our use, but I would appreciate a reply
either with another way to use the API or with a confirmation that this
is a bug which will be fixed in a later release.

 

Thanks,

 

Dan Perl

Taral Networks

Ottawa, Canada

 

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