Question

我正在尝试打印出一个双向链表。我能够从头到尾打印列表。然而，当我尝试从头到尾打印只有头部打印。这是代码的最后一部分。我已经包含了链接列表代码。有什么建议吗？

*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(cCURRENT))
      PRINT 5,CURRENT%PERSON
      PRINT 10,CURRENT%AGE
      CURRENT => CURRENT%PREV
  END DO

Answer 1

您使PREV指针无效，从而破坏了反向链接：

*CHANGE TAIL POINTER TO NEW END
          TAIL => CURRENT
          NULLIFY(CURRENT%NEXT)
          NULLIFY(CURRENT%PREV) <--- THE PROBLEM LIES HERE

双重链表Fortran。从尾到头打印。

1 个答案: