Zero length array, possible bug report

NCL team,

I'm reporting a fairly simple case where NCL creates a zero length
memory array. See log below. According to previous discussions, NCL
should not be able to do this, so it's a bug. On the other hand, are
you starting to sneak in support for zero length arrays? ;-)

I report this as a curiosity only, since I can probably protect myself
with something like getfilevardimsizes.

--Dave

On Wed, Feb 8, 2012 at 3:52 PM, David Brown <dbrown@ucar.edu> wrote
[IN PRIVATE REPLY]:
> Hi Dave,
>
> The answer is that it should not be possible in NCL to get an empty array. As you note for the ind() function, the correct response for NCL is to return a single element array (which in NCL is equivalent to a scalar) containing a missing value. If you encounter a situation where an empty, 0-sized array is created, then it is a bug. Interestingly, just this week I encountered this bug in the case of an HDF4 file that contains only image data and no scientific data sets. Since NCL cannot currently read the image data, from its perspective this file contains no variables and no dimensions. The functions getfilevarnames and getvardims were both returning empty arrays in this situation. This has now been fixed such that they return a single missing element.
> Hope that answers your question.
> -dave

mac11:~/translate/era 12> ncdump -h -s uwind.1979-2011.nc
netcdf uwind.1979-2011 {
dimensions:
        time = UNLIMITED ; // (0 currently)
variables:
        float time(time) ;
                time:long_name = "time" ;
                time:units = "days since 1960-01-01" ;
                time:_Storage = "chunked" ;
                time:_ChunkSizes = 16384 ;
--- ETC. ---
// global attributes:
                :_Format = "netCDF-4 classic model" ;

mac11:~/translate/era 13> ncl
 Copyright (C) 1995-2012 - All Rights Reserved
 University Corporation for Atmospheric Research
 NCAR Command Language Version 6.1.0
 The use of this software is governed by a License Agreement.
 See http://www.ncl.ucar.edu/ for more details.
ncl 0> f=addfile("uwind.1979-2011.nc","r")
ncl 1> time=f->time
warning:FileReadVar: time contains a 0 length dimension
warning:FileReadVar: time contains a 0 length dimension
ncl 2> print (dimsizes(time))
(0) 0
ncl 3> printVarSummary (time)

Variable: time
Type: float
Total Size: 0 bytes
            0 values
Number of Dimensions: 1
Dimensions and sizes: [time | 0]
Coordinates:
            time: [no elements]
Number Of Attributes: 5
  long_name : time
  units : days since 1960-01-01
  calendar : gregorian
  increment : 4 times daily
  actual_range : ( 9.999e+30, -9.999e+30 )
ncl 4>
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Received on Sat Dec 22 14:38:42 2012