Mark gave some excellent standards for dealing with lists.

One good way to ensure you delete a list and reset the list id is to do this:

if somelist >0 and listlen(somelist)>=0 then somelist=dellist(somelist);

DelList() returns a 0 if successful, and is good candidate value for an 'ex-list' id.

I typically use a less robust (but will move up to the more robust use of listlen() ) if somelist then somelist=dellist(somelist);

To simplify the whole concept, macroize it (the macro can be defined anywhere (even in the SCL), I suggest an autocall library)

%macro DELLIST (aList,recurse=N); if &aList > 0 and listlen (&aList) >= 0 then &aList = dellist (&aList,&recurse); %mend;

... a=makelist(); b=makelist(); c=makelist(); ... %dellist (a) %dellist (b) %dellist (c)

I leave the exercise of replacing <aList> (macro var containing one variable name [whose value is a list id]) with <lists> (macro var containing space separated list of variable names [whose values are list ids]) to the curious.

"Mark Bodt" <markbodt@STSS.CO.NZ> wrote in message news:3.0.5.32.19991218144914.015c2a50@pop3.paradise.net.nz... > At 12:30 17/12/99 -0500, you wrote: > >SAS-L, > > I recently became aware of the fact that SCL lists remain in memory > unless explicitly deleted. What prompted me to discover this fact was > >the observation that one SCL entry was eating LOTS of RAM because of > >a huge list that I created. I am writing the SCL code to execute on a > >server where many SAS sessions may be running, so efficiency is of > >utmost importance. Are there any other issues that I could be > >unpleasantly surprised with in terms of memory use or processor speed? > >In general, what are some tips on how to write efficient SCL code? > >Are there any books? > > > >Thanks, > >David Ward > > > > > >-- > >-------------------------------------- > >David L. Ward, Senior Software Developer > >DZS Software Solutions, Inc. > >Bound Brook, NJ > >SAS Related: dward@sashelp.com > >Work Related: dward@dzs.com > >-------------------------------------- > >-- > > > > David, > below is a tip I posted some time (years?) ago. > > Memory Leaks and deleting lists without errors. > > When you work with SCL lists, they are held in memory. If a program or > method creates a list, but does not delete it on termination and the > program or method is repeatedly called then available memory will > progressively diminish. This phenomenon is called a memory leak. It is > therefore crucial to ensure that lists are removed from memory when they > are no longer required. > > To delete a list use the function: rc=dellist(listid); > > Where listid is the list identifier of the list you wish to delete. Note > that if the list identifier is invalid then a program halt will occur. To > avoid this situation, the listlen(listid) function can be used in the > following way: > > If listlen(listid)>=0 then rc=dellist(listid); > > The listlen function returns the length of the list identified in the > variable listid . If the list is empty then it will return 0. If the list > has items it, then the function will return the number of items. If the > list is invalid then a negative value is returned. > > It is also could practice to said the list identifier to missing up the > list has been deleted. The reason for this is that SAS may recycle the > number used to identify the list. Consider the following code: > > *create a list; > List1=makelist(); > > *code to insert some items into the list; > > *delete the first list; > If listlen(list1)>=0 then rc=dellist(list1); > > /*Note that the first list has been deleted, but the list identifier list1 > still contains a number which used to point to list1 */ > > *create a new list called list 2; > List2=makelist(); > > *try to delete list1 again; > If listlen(list1)>=0 then rc=dellist(list1); > > When list2 was created, SAS may have recycled the list identifier. This > means that the variables list1 and list2 may have the same number. When an > attempt is made to delete list1 again, because list1 and list2 contain the > same identifier, then list 2 is deleted in error. By adding the line > > Listid=.; > > Immediately after deleting list1, we remove any references to any new lists > that are created. > > > > HTH > > > Mark > > > +------------------------------------------+--------------------------+ > | Mark Bodt | | > | Sunken Treasure Software Systems Ltd | SAS Institute(NZ) Ltd. | > | Specialising in SAS(R) Software | Quality Partner. | > | Consultancy in the Asia / Pacific Region | | > +------------------------------------------+--------------------------+ > | PO Box 9472, Marion Square, Wellington, New Zealand | > | Ph (025) 725 386 Fax +64 4 385 8670 Email: markbodt@stss.co.nz | > +---------------------------------------------------------------------+