[netcdfgroup] arrays of fixed-length strings

[Jeff Whitaker]

John Caron wrote:
>
>
> Jeff Whitaker wrote:
>> Ed Hartnett wrote:
>>> Jeff Whitaker <jswhit at fastmail.fm> writes:
>>>
>>>  
>>>> In netcdf-4.0, I don't see how to create variables which are arrays of
>>>> strings with length > 1.  I see how to create arrays of
>>>> single-characters, and arrays of variable-length strings, but not
>>>> strings of a specified length.
>>>>
>>>> Am I missing something, or is this not supported by HDF5?
>>>>
>>>>     
>>>
>>> Howdy Jeff!
>>>
>>> Strings are variable length by their nature.
>>>
>>> How about a two dimensional array of NC_CHAR?
>>>
>>> Thanks,
>>>
>>> Ed
>>>
>>>
>>>   
>>
>>
>> Ed:  I use arrays of fixed length strings, padded with spaces, quite 
>> a bit.  This simplifies the memory management issues associated with 
>> arrays of variable length strings (which have no counterpart in 
>> Fortran 90/95, although they are allowed in Fortran 2003).  Below is 
>> an excerpt from my previous reply which explains why I don't like 
>> using 2-D arrays of characters to represent 1-D arrays of 
>> fixed-length strings:
>>
>> Russ: I realize you can use a array of shape ndim,8 to store an array 
>> of ndim 8 character strings.  Thats the way I've done it with 
>> netcdf-3 - it just feels clunky.  A typical use case for me is 
>> station data, where you want to store the name of the station. I end 
>> up the with an array of characters shaped (nstations,ncars) -  in 
>> fortran I read it into an  (nstations,nchars) character(len=1) array 
>> (after first finding out what both nstations and nchars are), then 
>> reshape it into a (nstations) character(len=nchars) array.  I'd 
>> rather just read it into a character(len=nchars) array straight off.  
>> Not a show stopper for sure, but it would be more convenient.  I 
>> realize that specifying the data type would be tricky,  instead of 
>> NC_CHAR, do you have a bunch of new types NC_CHAR1, NC_CHAR2, ... 
>> NC_CHAR120?  Or a new function datatype = nc_set_chartype(nchars)?  
>> However, I bet it would get used a lot more than the esoteric 
>> datatypes you have in netcdf-4 already (enums and opaque for example).
>
> Hi Jeff:
>
> Suppose we stuck with fixed length char arrays for this case, but 
> added a convenience method in the API that did the work for you. What 
> would that convenience method look like?
>
> John

John:  A convenience method won't really help much - the thing I'd most 
like to avoid is defining another dimension to hold the number of 
characters in each string.  Essentially, I'd like to have that 
information transferred to the datatype.

-Jeff

-- 
Jeffrey S. Whitaker         Phone  : (303)497-6313
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