Re: [h5md-user] Mandate Variable-length string datatype

[Felix Höfling]

Am 23.09.2013, 17:38 Uhr, schrieb Peter Colberg
<address@hidden>:

> On Mon, Sep 23, 2013 at 10:43:39AM +0200, Felix Höfling wrote:
> > I'm not in favour of restricting the string types and also not of
> > variable-length strings.
> >
> > I don't see any benefit for the file format in such a restriction.
> >
> > From a C++ perspective which hides memory allocation in std::string for
> > instance, reading a fixed string is much easier. Otherwise, one has to
> > read a C-string first and to copy to std::string second. (I definitely
> > don't want to return a plain C-string in C++) For low-level languages  
> > the
> > converse is true. Eventually, reading a string will go to a single
> > function inside the reader program and there it is not too much pain to
> > implement both types of strings IMO.
>
> Abstractions are very hard to get right. To day I have not seen a
> single C++ interface to HDF5 that is useful beyond the initial goals
> at its conception.
>
> While it is important to have high-level interfaces that guide new
> H5MD users (e.g., pyh5md), it is equally important to support those
> users that write high-performance programs using the HDF5 API.
>
> Keeping the choice between fixed- and variable-length strings will
> simply mean that many writers and readers will not be interoperable,
> even if they use the same domain-specific data.

I don't get your point. Why are readers and writers not interoperable? The
only thing needed is that the reader queries the type of string using
H5Tis_variable_str() and acts accordingly. These are just a few lines
which are needed once in a function read_string().

The writer can write fixed or variable-length strings as it likes.

Felix