Another option would be to play the relational database game and split 'offsets' into a different dataset. Connect the items with some key (an index?) and perhaps a length. Of course connecting the dots is a manual procedure.
Depending on what you're doing this might not be terribly efficient. I've used this pattern a fair amount. Most of my accesses are sequential, so I can just maintain an index for each dataset. In this case, getting the next set of offsets is an increment while keys match.
Scott
···
From: Hdf-forum [mailto:hdf-forum-bounces@lists.hdfgroup.org] On Behalf Of Gerd Heber
Sent: Monday, October 28, 2013 5:13 PM
To: HDF Users Discussion List
Subject: Re: [Hdf-forum] Creating/storing data of variable length compound members
Nick, there's, as usual, no single right answer.
What's the average length of 'offsets' and what's
the length variability?
( 'size_t' is not a good starting point for a machine
independent representation.)
Representing 'offsets' a VLEN has its price: you'll loose
some performance and the ability to use compression on the data set.
If there's a sensible upper bound on the length and only slight
variation in the length, you might stick with a (fixed-size) ARRAY
component.
A compromise would be to separate the two parts of your compound
and have a 'bounding boxes' (+ HDF5 reference) dataset and an 'offsets'
dataset. Entries in the former would be compounds of your
bounding boxes and an HDF5 region reference into a global
'offsets' dataset. (In this simple case, you can think of a region
reference as a (offset, count) pair which references a contiguous
region in a global 'offsets' dataset.)
G.
From: Hdf-forum [mailto:hdf-forum-bounces@lists.hdfgroup.org] On Behalf Of Nicholas Yue
Sent: Monday, October 28, 2013 3:53 PM
To: HDF Users Discussion List
Subject: [Hdf-forum] Creating/storing data of variable length compound members
Hi,
I would like to store a collection of the following as a compound data
struct MyBox {
double minX;
double minY;
double minZ;
double maxX;
double maxY;
double maxZ;
std::vector<size_t> offsets;
};
I have no problem with the POD min* and max*
However, I am unsure how best to handle std::vector<size_t>
I read about variable length for string and was wondering if the information is applicable.
Which example code should I consult to have a better understand of variable length as used within a compound type ?
Cheers
--
Nicholas Yue
Graphics - RenderMan, Visualization, OpenGL, HDF5
Custom Dev - C++ porting, OSX, Linux, Windows
http://au.linkedin.com/in/nicholasyue
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