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Weird error nullifying a pointer

 
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ursuselasticus



Joined: 26 Mar 2005
Posts: 57

PostPosted: Fri Aug 19, 2022 7:13 pm    Post subject: Weird error nullifying a pointer Reply with quote

The below code gives me the error "Reference to undefined variable ..." and I am at my wit's end tracking it down.

Code:

   subroutine EG_Plants()

    use EG_Data
   implicit none

      integer EG_NewPlant
    integer EG_KillPlant

    integer iRslt

    type (Plants), pointer :: pPlantOld

    if (iiTSeed .eq. iiNTage)  then
         iRslt = EG_NewPlant (50, 'Aussaat')
        return
    endif

    if (iiNPlants .le. 0) return

   pPlantOld => ppPlantHead
    print *,pPlantOld%iID             ! <--

   ppPlantCurrent => ppPlantHead

!   Lebenslauf der Pflanzen

    do
      print*, ppPlantCurrent%iID  ! <--

      pPlantOld => ppPlantCurrent
        print*, pPlantOld%iID                 ! <--       
      nullify (pPlantOld)



(Sorry, I did not find a way to have line numbers added)

The error occurs in the last line printed here, when the pointer pPlantOld is to be nullified. I added some print-lines to check the contents of the pointers marked with ! <--. They work just fine and I receive three prints of the same ID-Number. Note: Variables with double leading characters are defined in module EG_Data.

What beats me is that I can have the contents of pPlantOld printed in one line - and in the very next line this pointer is undefined. And even if the status of this pointer may be undefined, this should not affect the nullify-operation, shoudn't it?
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ursuselasticus



Joined: 26 Mar 2005
Posts: 57

PostPosted: Fri Aug 19, 2022 11:03 pm    Post subject: Reply with quote

Strange but I got it.

It was not the line that the compiler diagnostics pointed at (this was nullify(pPlantOld)) in the above listing, but the next one where there was a reference to an undefined variable!

Do not know how this came about, though.
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