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Wrong line number in runtime error-message

 
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ursuselasticus



Joined: 26 Mar 2005
Posts: 66

PostPosted: Sun Sep 25, 2022 12:45 pm    Post subject: Wrong line number in runtime error-message Reply with quote

Hi,

when executing my program I receive this errormessage

"Reference through dangling Fortran Pointer at adress ..."

but the line number indicated in the following detail apparently points to the wrong line:

Code:

            else
                 pPlantActual%iAge = pPlantActual%iAge + 1                           ! Alter um 1 erhöht
                if (pPlantActual%iAge .ge. pPlantActual%iSeedSurvivalActual) then
                    print *,'Vertrocknet: Samen Nr. ', pPlantActual%iNumber
                     iRslt = EG_KillPlant(pPlantActual)                        ! Wenn vertrocknet, dann löschen
                    cycle
            endif
       


The line indicated is the cycle statement.
The pointer pPlantActual gets deallocated and nullified in EG_KillPlant.

I added the print-statements prior to this line. This executes without any issue.

I am using FTN95, version 8.80 (personal edition) with Plato 5.4.0 in a Windows11 environment. The code was compiled with /x64.

Cheers
Norbert
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ursuselasticus



Joined: 26 Mar 2005
Posts: 66

PostPosted: Sun Sep 25, 2022 6:32 pm    Post subject: Reply with quote

Finally I was able to pinpoint this nasty bug - but at a completely different location than flagged by this errormessage (see my previous posting).

Here is the first part of the routine in Question:
Code:

   subroutine EG_Plants()

    use EG_Data
   implicit none
    include <windows.ins>,nolist

    INTERFACE
       integer function EG_KillPLant(pPlantActual)
        type (Plants), pointer :: pPlantActual
        end function EG_KillPlant

        integer function EG_NewPlant (pMother, cMode)
        type (Plants), pointer :: pMother
      character(*), intent(in) :: cMode
        end function EG_NewPlant       
    END INTERFACE

      integer EG_NewPlant
    integer EG_KillPlant

    character*20 cBuffer

    integer iRslt
    integer EG_Pause

    type (Plants), pointer :: pPlantNext
    type (Plants), pointer :: pPlantActual                  ! Zeiger auf aktuelle Pflanze.

   iRslt = 0
    iRslt = iRslt   ! Vermeiden der Warnung

    if (iiTSeed .eq. iiNTage)  then
         nullify (ppPlantCurrent)
         iRslt = EG_NewPlant (ppPlantCurrent, 'AUSSAAT')      ! ppPlantCurrent wird bei der Aussaat eigentlich nicht gebraucht!
        return
    endif

    if (iiNPlants .le. 0) return
   pPlantNext => ppPlantHead
   
!   Lebenslauf der Pflanzen

    do
      if (.not. associated(pPlantNext)) exit
        pPlantActual => pPlantNext
        nullify (pPlantNext)
        if (associated (pPlantActual%pNext)) pPlantNext => pPlantActual%pNext

!      Keimung und ggf. Vertrocknen der Samen

      if (pPlantActual%lSeedFlag) then                                             ! Wenn dieses Teil noch Samen ist ...
              if (ttPlanSquares(pPlantActual%iPlanX, pPlantActual%iPlanY)%iWater .gt. 0) then       ! ... und es gibt Wasser
               pPlantActual%iWater = min (iiMaxValue, pPlantActual%iWater + 1)                  ! dann Wasser um 1 erhöhen
                if (pPlantActual%iWater .gt. pPlantActual%iSeedWater) then                     ! Wenn die gespeicherte Wassermenge die zum Keimen erforderliche Menge übersteigt, dann keimen               
                     pPlantActual%lSeedFlag = .false.
                    pPlantActual%iAge = 0
                    pPlantActual%iWater = 0
               pPlantActual%iTNextSpread = iiNTage + pPlantActual%iSpreadMinAge
                    iiNSeeds = iiNSeeds - 1
                endif
            else
                 pPlantActual%iAge = pPlantActual%iAge + 1                                 ! Restlebensdauer als Samen um 1 verringert
                if (pPlantActual%iAge .ge. pPlantActual%iSeedSurvivalActual) then
                     iRslt = EG_KillPlant(pPlantActual)                                    ! Wenn vertrocknet, dann löschen
                    cycle                              ! < - this was the line flagged by the errormessage
            endif
            endif
        else            ! Ist kein Samen mehr, sondern gekeimte Pflanze

!         Alter, Tod wenn maximalalter überschritten
           
!         pPlantActual%iAge = ppPlantCurrent%iAge + 1         ! < - This was the faulty codeline
         pPlantActual%iAge = pPlantActual%iAge + 1         ! < - This is the proper codeline.      

            if (pPlantActual%iAge .gt. pPlantActual%iPlantMaxAgeActual) then
                 iRslt = EG_KillPlant(pPlantActual)                           ! Wenn überaltert, dann löschen
                cycle
            endif


Second part will follow with my next reply.

I indicated where the error was flagged and the codeline that proved faulty in reality, that is, where this dangling pointer occurred. Note: the loop was processed three times after the flagged line was processed for the last time before the error occurred.

I am happy with my program running - but somebody might be interested to look into this matter.
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ursuselasticus



Joined: 26 Mar 2005
Posts: 66

PostPosted: Sun Sep 25, 2022 6:36 pm    Post subject: Reply with quote

Just for completion: here is the final part of the code:

Code:

   

!         Wasseraufnahme und Verbrauch, Tod, wenn Wasser = 0   
         
         if (ttPlanSquares(pPlantActual%iPlanX, pPlantActual%iPlanY)%iWater .gt. 0) then       ! wenn es Wasser gibt, dann          
            pPlantActual%iWater = pPlantActual%iWater + pPlantActual%iWaterGetActual         ! Steigt der Wassergehgalt
                pPlantActual%iWater = min (pPlantActual%iWater, pPlantActual%iWaterCapacityActual)   ! bis zum Maximum
            else
            pPlantActual%iWater = pPlantActual%iWater - pPlantActual%iWaterUseActual         ! sonst sinkt er
                if (pPlantActual%iWater .le. 0) then                                    ! wenn kein Wasservorrat mehr vorhanden
                    iRslt = EG_KillPlant(pPlantActual)                                    ! vertrocknet die Pflanze
                endif
                cycle
            endif

!         Wachstum
!         Idee: Wchstumspotenzial aufteilen zwischen  Wurzel / Pflanze / Schutz (=Stamm). Wasser versickern lassen. Begrenzte Kapazität Wurzel.

         if (pPlantActual%iWater .ge. pPlantActual%iGrowWaterNeededActual) then               ! Sofern genügend Feuchtigkeit gespeichert ist:
               pPlantActual%rSize = pPlantActual%rSize + pPlantActual%rPlantGrowStepActual         ! Wachsen
                pPlantActual%iWater = pPlantActual%iWater - pPlantActual%iGrowWaterUsedActual      ! und Wasser verbauchen
                if (pPlantActual%rSize .gt. pPlantActual%rPlantMaxSizeActual) then               ! Wenn aber die Maximalgröße erreicht ist
                     pPlantActual%rSize = pPlantActual%rPlantMaxSizeActual                     ! dann bleibt es bei der Maximalgröße
               pPlantActual%iWater = pPlantActual%iWater - pPlantActual%iGrowWaterUsedActual   ! und das Wasser wird nicht verbraucht
                endif
                pPlantActual%rRBlocked = pPlantActual%rSize / 2.0
            endif

!         Vermehrung

         if ((iiNTage .gt. pPlantActual%iTNextSpread) .and. (pPlantActual%iWater .gt. pPlantActual%iSpreadMinWaterActual) .and. (pPlantActual%rSize .gt. pPlantActual%rSpreadMinSizeActual)) then
                pPlantActual%iTNextSpread = iiNTage + pPlantActual%iSpreadPeriodActual
             iRslt = EG_NewPlant(pPlantActual, "VERMEHRUNG")

         endif
        endif
    enddo

    return
    end


If somebody could point out a way to a proper format for code it would be appreciated.

Cheers
Norbert
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PaulLaidler
Site Admin


Joined: 21 Feb 2005
Posts: 7481
Location: Salford, UK

PostPosted: Mon Sep 26, 2022 7:38 am    Post subject: Reply with quote

It is possible that the line numbers are not exactly right. There has been one or more related bug fixes for FTN95 v8.90.

I have not looked at the detail of the code presented here. I would need a fully working sample in order to understand what is happening.

As a general rule, the point at which the program fails (for a dangling pointer error) is not the same as the line where the programming error occurs. Here is a simple example which requires (for example) the command line option /checkmate.

Code:
program allocation
    integer, allocatable, target :: p1(:)
    integer, pointer :: p2(:)

    print*, "Program entered."
    allocate(p1(10))
    p2 => p1
    call destroy
    p2 = 10
    print*, "Program terminated, logical error not detected."

contains
    subroutine destroy
        deallocate(p1)
    end subroutine
end


The call to destroy is an error. p2 = 10 fails.
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ursuselasticus



Joined: 26 Mar 2005
Posts: 66

PostPosted: Mon Sep 26, 2022 4:02 pm    Post subject: Reply with quote

Yes, it is perfectly clear, that the programming error can be at a completely different piece of code from where the error finally manifests itself and in case of a fatal error, execution is aborted.

In your example the error message flags line #9 which is the statement, that could not be executed (p2 = 10).

In my case however the flagged line was not the one where the error manifested itself.

Cheers
Norbert

P.S. The next time I have such an error, I will forward a copy of my code to you.
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