Re: [h5md-user] Strings again / parallel issue

[Pierre de Buyl]

On Thu, Feb 06, 2014 at 09:39:47AM -0500, Peter Colberg wrote:
> On Thu, Feb 06, 2014 at 10:11:36AM +0100, Felix Höfling wrote:
> > Saying Goodbye to mandating VL String is a good idea! But why forcing the
> > string to be of fixed-length now? Why don't we let the user decide,
> > depending on the situation? I think we had good reasons earlier to use
> > variable length strings. And we might soon encounter a case where
> > variable-length strings would be preferred.
> 
> With variable-length strings, the caller needs to pass or receive an
> array with pointers to character strings; with fixed-length strings,
> an array of characters. The former is negligibly easier than the
> latter in C, but significantly harder in Fortran (and requires
> iso_c_binding); thus the preference for fixed-length strings.

Actually, I have the feeling that variable-length "whatever" in HDF5 should be
used only when there is no choice (i.e. data for which you have significant
variations in the size of each element).

This comes from:
1. the fact that the vl-string attribute routine is missing in Fortran 90.
2. h5py's documentation
http://docs.h5py.org/en/latest/strings.html#compatibility
3. VL is reported not to work in parallel settings in the HDF5 FAQ

So making the choice may actually prevent us from shooting ourselves in the foot
:-)

P