20040913: netCDF Access Violation error in Fortran

Elizabeth,

> To: address@hidden
> From: Elizabeth North <address@hidden>
> Subject: Access Violation error in Fortran
> Organization: University of Maryland
> Keywords: 200409121151.i8CBpInJ007499 netCDF Fortran

The above message contained the following:

>   I am trying to access a portion of an array from a large .nc file. When
> the program gets to the line with STATUS = NF_GET_VARA_REAL it aborts
> (before it assigns a STATUS error message). Compac Visual Fortran
> debugger has the error message "Access Violation". I thought the file
> could be corrupt, but I can read in the entire array without a problem.
> It just happens when I use the NF_GET_VARA_REAL statement. I've pasted
> the relevant code below. If you have any advice on what I can do to avoid
> the error, I'd really appreciate it!

Off the top of my head, there are several posibilities:

    1.  The start-vector (startb) is incorrect.  Does the following 
        statement

            startb=1

        assign 1 to every element of startb?

    2.  The count-vector (rendb) is incorrect.

    3.  The receiving array (U) is too small.  It's 3-D.  Does it need
        to be 4?

Basically, there's got to be a mismatch between the amount of the array
you're trying to read and the space available in which to put the
values.

Information on the Fortran-77 start- and count-vectors can be found at

    http://my.unidata.ucar.edu/content/software/netcdf/guidef/

> Regards,
> Elizabeth North
> Assistant Research Scientist (soon to be Assistant Professor)
> University of Maryland
> Center for Environmental Science
> Horn Point Laboratory
> 2020 Horns Point Road
> Cambridge, MD 21613 USA
> phone: (410) 221-8497
> fax: (410) 221-8490
> 
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>       program main
>       include 'netcdf.inc'
>       REAL U(81,122,20),Uvelb(81,122,20),Uvelc(81,122,20),
>       1  Uvelf(81,122,20),hc,days,seconds,daytime
>       integer time,dt,iint,counter,counter2,counter3,
>      1  stepf,stepc,stepb,stepT,timem,prcount,iprint,printdt,
>      2  imu,jmu,kmu,
>      4  startb(4),rendb(4),startc(4),rendc(4),startf(4),rendf(4)
>       CHARACTER prefix*5,suffix*3,buffer*30,filenm*15
>       integer NCID,STATUS,NVARS,dimcount(4),dimids(4),ndims,idv_u
>    . . .
> c    Open netCDF file
>       counter=iint+180
>       prefix='kklw_'
>       suffix='.nc'
>       WRITE(buffer,'(A,I3,A)') prefix,counter,suffix
>       READ(buffer,'(A)') filenm
>       write(*,*) filenm
> c
>       STATUS = NF_OPEN(filenm, NF_NOWRITE, NCID)
>       if (STATUS .NE. NF_NOERR) write(*,*) 'Problem NF_OPEN'
>       write(*,*) 'ncid = ', ncid
> 
> c **** U velocity
>       STATUS = NF_INQ_VARID(NCID,'u',idv_u)
>         write(*,*) 'u varID =', idv_u
>       STATUS = NF_INQ_VARNDIMS(NCID,idv_u,ndims)
>       status = NF_INQ_VARDIMID(NCID,idv_u,dimids)
>       write(*,*) ' ndims =',ndims
>       write(*,*) ' dimids =',dimids
>       do i=1,ndims
>       STATUS = NF_INQ_DIMLEN(NCID,dimids(i),dimcount(i))
>           !write(*,*) 'u dim ',i,' = ',dimcount(i)
>       enddo
>       imu= dimcount(1)
>       jmu= dimcount(2)
>       kmu= dimcount(3)
>       timem= dimcount(4)
>       write(*,*) ' u- imu,jmu,kmu,timem = ',imu,jmu,kmu,timem
>       rendb(1) = imu
>       rendb(2) = jmu
>       rendb(3) = kmu
>       rendb(4) = stepb
>       startb=1
>       U=0.0
>       write(*,*) ' rendb',rendb(1),rendb(2),rendb(3),rendb(4)
>       write(*,*) ' startb',startb(1),startb(2),startb(3),startb(4)
>       STATUS = NF_GET_VARA_REAL(NCID,idv_u,startb,rendb,U)
>       if (STATUS .NE. NF_NOERR) write(*,*) 'Problem read array'
>       do 40 kk = 1,kmu
>         do 41 jj = 1,jmu
>           do 42 ii = 1,imu
>            Uvelb(ii,jj,kk) = U(ii,jj,kk)
>  42       continue
>  41     continue
>  40   continue

Regards,
Steve Emmerson

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