[hdf-forum] Correct practice with C++ API

[Quincey Koziol]

Hi Ben,

On Mar 10, 2009, at 1:41 PM, Benjamin Scherrey wrote:

>    I've made a little progress since before. Have a few specific
> questions and would appreciate any pointers or best practices on how
> to accomplish these things with the C++ api:
>
> 1. I still can't seem to read bool values back for some reason. What
> is the correct NATIVE_XXX type to use or should I be mapping to
> something other than C++ boolean?

	Currently, the HDF5 library doesn't support the native C & C++  
booleans types, but rather the "hbool_t" type we define in our header  
files.  At some point, we will alias hbool_t to the native boolean  
types, but that requires some more work.

> 2. How does one control the quantity of results coming back from
> DataSet::read()? All the behaviour I see points to it returning the
> entire dataset. Some of my records have a million+ instances so that's
> a lot of stuff to be manipulating in memory at once. How do I start at
> a certain offset and read in a select quantity of items via the
> DataSet (or some other) class?

	You want to define a selection on the file & disk dataspaces.  See  
H5Sselect_hyperslab() and H5S_select_elements() for example.

> 3. I'm not yet writing to HDF5 via C++ but, once I do, I imagine I
> will have the same question regarding DataSet::write().

	Ditto.

		Quincey


>    I'm attaching an updated version of yesterdays code so you can see
> what I'm trying to do. Appreciate any advice on my approach here.
>
> thanx,
>
>  -- Ben Scherrey
>
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