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linked list example [message #12683]

Wed, 02 September 1998 00:00

Doug Larson
Messages: 10
Registered: September 1998

Junior Member

Here is a set of linked list modules I made for my own use. I hesitate
to
post themsince they are not "bullet-proof" but they do the job.
Hopefully
someone will be inspired to write a better open source linked list
library.

My system administrator would not buy the "Fanning" book for me due to
tight
resources, so I had to invent my own (kluge) solutions.

Cheers,
Douglas J. Larson, PiledHigher&Deeper
Space Radiation Lab
California Institute of Technology
Mail Code: 220-47
Pasadena, CA 91125

; ************************************************************ ******************
;+
; Setup_llist.pro
;
; PURPOSE:
; Setup a new node of a generic linked list.
;
; CATEGORY:
; Generic linked list generator. This function is NOT an insert operator.
;
; CALLING SEQUENCE:
; somenewnode = ptr_new(Setup_llist(bugmsg))
;
; KEYWORD PARAMETERS:
;
; COMMON BLOCKS:
; None
;
; OUTPUTS:
; Data structure
;
; MODIFICATION HISTORY:
; Created by: Douglas J. Larson, 18 August, 1998.
;-
; ************************************************************ ******************
FUNCTION Setup_llist, bugmsg

if ( bugmsg eq 1 ) then message,' Entered', /INFORMATIONAL

lls = { nodePtr:PTR_NEW(), $ ; Points to the linked list information
next:PTR_NEW() } ; Pointer to the next data vector

if ( bugmsg eq 1 ) then message,' Exited', /INFORMATIONAL

RETURN, lls

END
; ************************************************************ ******************
;+
; llist_insert.pro
;
; PURPOSE:
; Setup a new node of a generic linked list.
;
; CATEGORY:
; Generic linked list generator. This function is NOT an insert operator.
;
; CALLING SEQUENCE:
;
; KEYWORD PARAMETERS:
;
; COMMON BLOCKS:
; None
;
; OUTPUTS:
; Data structure
;
; MODIFICATION HISTORY:
; Created by: Douglas J. Larson, 18 August, 1998.
;-
; ************************************************************ ******************
FUNCTION llist_insert, bugmsg, startPtr, value

if ( bugmsg eq 1 ) then message,' Entered', /INFORMATIONAL

if NOT(PTR_VALID(startPtr)) then begin
if ( bugmsg eq 1 ) then message,'startPtr is NULL', /INFORMATIONAL
startPtr = PTR_NEW(Setup_llist(bugmsg))
currentPtr = startPtr
endif else if (PTR_VALID(startPtr)) then begin
if ( bugmsg eq 1 ) then message,'startPtr is Valid', /INFORMATIONAL
currentPtr=startPtr
while (PTR_VALID(currentPtr)) do begin
previousPtr=currentPtr
currentPtr=(*currentPtr).next
endwhile
(*previousPtr).next = PTR_NEW(Setup_llist(bugmsg))
currentPtr=(*previousPtr).next
endif
(*currentPtr).nodePtr = value
(*currentPtr).next = PTR_NEW()

if(bugmsg eq 1 ) then begin
if NOT(PTR_VALID(value)) then begin
message,'value is NULL', /INFORMATIONAL
endif else begin
message,'value is Valid', /INFORMATIONAL
endelse
if(NOT(PTR_VALID(startPtr)) or NOT(PTR_VALID(currentPtr)))then begin
print,'PTR_VALID(startPtr)=',PTR_VALID(startPtr)
print,'PTR_VALID(nextPtr)=',PTR_VALID(nextPtr)
print,'PTR_VALID(currentPtr)=',PTR_VALID(currentPtr)
endif
endif

if ( bugmsg eq 1 ) then message,'Exited', /INFORMATIONAL

RETURN, currentPtr

END
; ************************************************************ ******************
;+
; PURPOSE:
; Return the pointer to the desired record in the linked list.
;
; CALLING SEQUENCE:
;
; EXAMPLE:
;
; REQUIRED ROUTINES:
;
; VARIABLES:
; bugmsg - Debugging message activator (0-No messages, 1-verbose mode)
;
; MODIFICATION HISTORY:
; Created: Douglas J. Larson, 05 August, 1998.
;
;-
; ============================================================ ==================
function llist_lookup, bugmsg, startPtr, key, criteria

if(bugmsg eq 1) then message,' Entered', /INFORMATIONAL

if NOT(PTR_VALID(startPtr)) then begin
if ( bugmsg eq 1 ) then message,'startPtr is NULL', /INFORMATIONAL
retval = PTR_NEW()
endif else if (PTR_VALID(startPtr)) then begin
if ( bugmsg eq 1 ) then message,'startPtr is Valid', /INFORMATIONAL

; Create a pointer to the heap variable pointed at by _startPtr_.
currentPtr = startPtr

uckey = STRUPCASE(key)

tag_number = where(tag_names((*(*currentPtr).nodeptr)) eq uckey, count)
if(bugmsg eq 1) then begin
print,'counter=',count,' uckey=',uckey,' tag_number=',tag_number
endif

done = 0
while (done eq 0) do begin
if(bugmsg eq 1) then begin
text='Tag String Requested='+key
message, text, /INFORMATIONAL
help,criteria
;help,(*currentPtr).(tag_number[0])
endif
if(criteria eq (*(*currentPtr).nodeptr).(tag_number[0])) then begin
retval = (*currentPtr).nodeptr
done = 1
endif else begin
; Move to the next link in the list
currentPtr = (*currentPtr).next
if(ptr_valid(currentPtr) eq 0) then begin
retval = ptr_new()
done = 0
endif
endelse
endwhile
endif

if(bugmsg eq 1) then message,' Exited', /INFORMATIONAL

RETURN, retval
END
; ************************************************************ ******************
;+
; llist_print.pro
;
; PURPOSE:
; Print a specified node element of an entire generic linked list.
;
; CATEGORY:
; Generic singly linked list.
;
; CALLING SEQUENCE:
; llist_print, bugmsg, startPtr, fieldwanted
;
; KEYWORD PARAMETERS:
;
; COMMON BLOCKS:
; None
;
; OUTPUTS:
; Data structure
;
; MODIFICATION HISTORY:
; Created by: Douglas J. Larson, 22 August, 1998.
;-
; ============================================================ ==================
FUNCTION llist_print, bugmsg, startPtr, fieldwanted

if ( bugmsg eq 1 ) then message,' Entered', /INFORMATIONAL

retval = 1
if NOT(PTR_VALID(startPtr)) then begin
if ( bugmsg eq 1 ) then message,'startPtr is NULL', /INFORMATIONAL
retval = 0
endif else if (PTR_VALID(startPtr)) then begin
; Create a second pointer to the heap variable pointed at by _startPtr_.
currentPtr = startPtr

; IDL likes all structure tags in uppercase.
fieldwanted = strupcase(fieldwanted)

tag_number = where(tag_names((*(*currentPtr).nodeptr)) eq fieldwanted, count)

if(count eq 0)then begin
message,'Tag is NOT in structure, check the code!'
retval = 0
endif else begin
; Traverse the linked list and print the list element information.
while PTR_VALID(currentPtr) do begin
print, currentPtr, ',named ', $
(*(*currentPtr).nodeptr).(tag_number[0]), $
', points to: ', (*currentPtr).next
currentPtr = (*currentPtr).next
endwhile
endelse
; PTR_FREE,currentPtr
endif

if ( bugmsg eq 1 ) then message,'Exited', /INFORMATIONAL

return, retval
end

Attachment: llist.txt
(Size: 6.11KB, Downloaded 97 times)

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Re: linked list example [message #12745 is a reply to message #12683]

Fri, 04 September 1998 00:00

mirko_vukovic
Messages: 50
Registered: January 1998

Member

In article <6sl5km$m7d$1@clam.niwa.cri.nz>,
"Mark Hadfield" <m.hadfield@niwa.cri.nz> wrote:
> A couple of comments:
>
> A linked list just cries out to be implemented as an object class. I wrote
> such a thing some time ago but will not post the code here for fear of
> ridicule.
>
actually, IDL_Container is a linked list. But it accepts only objects as its
elements (last time I looked, months ago)

Mirko

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Re: linked list example [message #12753 is a reply to message #12683]

Fri, 04 September 1998 00:00

davidf
Messages: 2866
Registered: September 1996

Senior Member

Mark Hadfield (m.hadfield@niwa.cri.nz) writes:

> A linked list just cries out to be implemented as an object class. I wrote
> such a thing some time ago but will not post the code here for fear of
> ridicule.

I routinely post code here when I don't have the time
or energy to fix it up myself. Someone always grabs it
and a day later e-mails me the "corrected" code with all
those features I should have added in the first place.

If I'm just searching for bugs, I announce that the
program "works" or is "the best program I've ever
written".

I've been thinking of myself lately as more of an
"idea person" rather than a "programmer". It's easier
on the ego. :-)

> Robert Mallozzi (Robert.Mallozzi@msfc.nasa.gov) has written some container
> classes, including a last-in-first-out stack and a first-in-first-out queue.
> The queue is useful when reading data from text files, to avoid the
> performance hit when extending arrays, as discussed here a week or two ago.

You know, even with as much free code as there is out there,
I find that not too many people use it. I don't really know
why. Perhaps it is just hard to read other people's code,
or maybe you don't really understand it unless you write
your own (my reason for writing a linked list rather than
using the one Beau Legeer uses in the Advanced Programming
classes). In any case, I found I had to write a book to
call any attention at all to the programs I offer.

Now that I think about it, maybe I should revisit the
notion of program quality. :-)

Cheers,

David

----------------------------------------------------------
David Fanning, Ph.D.
Fanning Software Consulting
E-Mail: davidf@dfanning.com
Phone: 970-221-0438, Toll-Free Book Orders: 1-888-461-0155
Coyote's Guide to IDL Programming: http://www.dfanning.com/

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Re: linked list example [message #12762 is a reply to message #12683]

Thu, 03 September 1998 00:00

Mark Hadfield
Messages: 783
Registered: May 1995

Senior Member

A couple of comments:

A linked list just cries out to be implemented as an object class. I wrote
such a thing some time ago but will not post the code here for fear of
ridicule.

Robert Mallozzi (Robert.Mallozzi@msfc.nasa.gov) has written some container
classes, including a last-in-first-out stack and a first-in-first-out queue.
The queue is useful when reading data from text files, to avoid the
performance hit when extending arrays, as discussed here a week or two ago.

--
Mark Hadfield, m.hadfield@niwa.cri.nz http://www.niwa.cri.nz/~hadfield/
National Institute for Water and Atmospheric Research
PO Box 14-901, Wellington, New Zealand

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Re: linked list example [message #12765 is a reply to message #12683]

Thu, 03 September 1998 00:00

davidf
Messages: 2866
Registered: September 1996

Senior Member

Doug Larson (djl@REMOVECAPSloki.srl.caltech.edu) writes:

> My system administrator would not buy the "Fanning" book
> for me due to tight resources, so I had to invent my
> own (kluge) solutions.

I'm sending Mr. Larson a book with my compliments for adding
to the code resources of this newsgroup. It's actually the
last one left of the original first edition. The updated
second edition hits the streets tomorrow. Many thanks to
all the generous people on this newsgroup who have bought
books and offered suggestions and corrections. The next
book will be coming "real soon now". :-)

Cheers,

David

----------------------------------------------------------
David Fanning, Ph.D.
Fanning Software Consulting
E-Mail: davidf@dfanning.com
Phone: 970-221-0438, Toll-Free Book Orders: 1-888-461-0155
Coyote's Guide to IDL Programming: http://www.dfanning.com/

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