Printing Doubly Linked List From Tail to Head

[turnerdaniet]

I AM TRYING TO PRINT OUT A DOUBLY LINKED LIST. I AM ABLE TO GET THE LIST TO PRINT FROM HEAD TO TAIL.. HOWEVER WHEN I PRINT TAIL TO HEAD ONLY THE HEAD WILL PRINT. THIS IS THE LAST PART OF THE CODE. I HAVE INCLUDED THE LINK LIST CODE. ANY SUGGESTIONS?

*INPUT UP TO EOF
NULLIFY(HEAD,TAIL)
DO WHILE(.TRUE.)
READ(1,*,END=999)NAMEIN
READ(1,*,END=999)AGEIN

*INITIALIZE THE POINTERS TO NULL
NULLIFY(CURRENT)
ALLOCATE(CURRENT)
CURRENT%PERSON = NAMEIN
CURRENT%AGE = AGEIN
*IF THERE IS NOT AT LEAST ONE NODE

IF(.NOT.ASSOCIATED(HEAD))THEN
HEAD => CURRENT
TAIL => CURRENT
NULLIFY(HEAD%NEXT,HEAD%PREV)

*IF THE CURRENT IS LAST NODE
ELSE
*PLACE AT END OF LIST

TAIL%NEXT =>CURRENT
CURRENT%PREV=>TAIL
NULLIFY(CURRENT%NEXT)

*CHANGE TAIL POINTER TO NEW END
TAIL => CURRENT
NULLIFY(CURRENT%NEXT)
NULLIFY(CURRENT%PREV)
END IF
END DO

999 CONTINUE

*PRINT FROM HEAD TO TAIL
*POINT TO THE BEGINNING
NULLIFY(TEMP)
TEMP => HEAD
*PRINT EACH NODE
PRINT *,'-----PRINTING fROM HEAD TO TAIL-----'
DO WHILE(ASSOCIATED(TEMP))
PRINT 5,TEMP%PERSON
PRINT 10,TEMP%AGE
TEMP => TEMP%NEXT
END DO

*PRINT FROM TAIL TO HEAD
*POINT TO THE BEGINNING
*PRINT EACH NODE
CURRENT => TAIL
PRINT *,'-----PRINTING fROM TAIL TO HEAD------'
DO WHILE(ASSOCIATED(TEMP))
PRINT 5,CURRENT%PERSON
PRINT 10,CURRENT%AGE
CURRENT => CURRENT%PREV
END DO

 

[gummibaer]

      PRINT *,'-----PRINTING fROM TAIL TO HEAD------'
      DO WHILE(ASSOCIATED(TEMP))  !<--- TEMP ??
          PRINT 5,CURRENT%PERSON
          PRINT 10,CURRENT%AGE
          CURRENT => CURRENT%PREV
      END DO

Norbert




The optimist believes we live in the best of all possible worlds - the pessimist fears this might be true.

 

[turnerdaniet]

It should be current. I have fixed that. It was was from previously when i used temp in place of current such as the head to tail loop

 

[gummibaer]

You are right. TEMP is left disassociated from the printing head to tail, so this loop should not execute at all, if TEMP was used.

But I Found this in your code

   *CHANGE TAIL POINTER TO NEW END
              TAIL => CURRENT
              NULLIFY(CURRENT%NEXT)
              NULLIFY(CURRENT%PREV)
         END IF    
      END DO

Seems that you nullify TAIL%PREV any time you add a new item to the list, so the back link does not exist.

Norbert

The optimist believes we live in the best of all possible worlds - the pessimist fears this might be true.