On Jun 3, 2010, at 9:23 AM, Mark Miller wrote:
> Ah, I see. Well, that is definitely different from what I was thinking
> he was asking. And, requires a different answer than I gave. ;)
Well, now he knows both pieces of information. :-)
Quincey
> Mark
>
> On Thu, 2010-06-03 at 04:39, Quincey Koziol wrote:
>> Hi Mark,
>>
>> On Jun 2, 2010, at 9:36 PM, Mark Miller wrote:
>>
>>> Yes. But the procedure you'd use depends a bit on what kind of object
>>> you are talking about (dataset or attribute) and how you chose to define
>>> the object. Did you use H5T_C_S1 as the datatype for the string? Did you
>>> maybe just define a dataset/attribute of type H5T_NATIVE_CHAR and then
>>> an 1D dataspace of some size? I think those choices effect how you'd go
>>> about obtaining length.
>>>
>>> A general algorithm might look like...
>>>
>>> 1. whether its a dataset or attribute, you need to open it first
>>> (H5Dopen/H5Aopen)
>>> 2. then get its datatype (H5Dget_type/H5Aget_type)
>>> 3. then get the size of that datatype (H5Tget_size)
>>> 4. Then get the size of the dataspace
>>> 5. Use results from steps 3 and 4 to determine total size.
>>
>> Actually, I think that Ken is trying to determine the actual string
>> length for an individual element of a dataset or attribute, and he's correct
>> that there's no way to retrieve the length before reading it in. The method
>> you describe above is correct for determining the size of the array an
>> application will need to allocate for reading the strings, but the size
>> returned from H5Tget_size() should be the same as sizeof(char *) (for
>> variable-length strings - for variable-length sequences of another datatype,
>> it should be sizeof(hvl_t)). The memory for the actual strings themselves
>> will be allocated at read time (and the malloc/free routines used can be
>> controlled with H5Pset_vlen_mem_manager).
>>
>> Quincey
>>
>>> Mark
>>>
>>> On Wed, 2010-06-02 at 18:55, Ken Sullivan wrote:
>>>> Quick question, is there a way to find the length of a variable length
>>>> string without first reading it?
>>>>
>>>> Thanks,
>>>> Ken
>>> --
>>> Mark C. Miller, Lawrence Livermore National Laboratory
>>> ================!!LLNL BUSINESS ONLY!!================
>>> [email protected] urgent: [email protected]
>>> T:8-6 (925)-423-5901 M/W/Th:7-12,2-7 (530)-753-851
>>>
>>>
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>>
>>
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> --
> Mark C. Miller, Lawrence Livermore National Laboratory
> ================!!LLNL BUSINESS ONLY!!================
> [email protected] urgent: [email protected]
> T:8-6 (925)-423-5901 M/W/Th:7-12,2-7 (530)-753-851
>
>
> _______________________________________________
> Hdf-forum is for HDF software users discussion.
> [email protected]
> http://mail.hdfgroup.org/mailman/listinfo/hdf-forum_hdfgroup.org
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