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

[Pierre de Buyl]

On Tue, Feb 04, 2014 at 06:24:48PM +0100, Felix Höfling wrote:
> Am 04.02.2014, 16:05 Uhr, schrieb Pierre de Buyl
> <address@hidden>:
> 
> I always felt uncomfortable with specialising to a certain String type. I
> suggest to drop "VL" and allow _any_ kind of HDF5 String type for the
> writer. The reader can easily handle the different cases by querying
> H5Tis_variable_str
> http://www.hdfgroup.org/HDF5/doc/RM/RM_H5T.html#Datatype-IsVariableString

Actually, I think it will avoid a lot of problems to define what kind of strings
we want. Aside from the purely practical aspect of writing less code, it also
avoids the question from a new user: "what kind of strings should I use?".
Removing this question makes it easier, in my opinion. Also, it decreases the
amount of documentation in, say, the "implementation" page of the h5md site.

I really didn't want to bring the debate back, but a solution in Fortran should
be available :-)

If, as it is discussed on the other sub-thread, you cannot use VL strings in
Fortran for the attributes (very specific case, but still), I'd prefer that we
mandate fixed-length.

Cheers,

Pierre


> For reading a string attribute, you may have a look at the code snippet
> below.
> 
> Regards,
> 
> Felix
> 
> PS: I've resent the message since it seemingly had not arrived at
> the list the first time.
> 
> std::string read_string_attribute(hid_t attr_id)
> {
>       std::string value;
>       hid_t type_id = H5Aget_type(attr_id));
>       htri_t is_varlen_str =  H5Tis_variable_str(type_id));
>       if (is_varlen_str > 0) {
>           // read fixed-size string, allocate space in advance and let the
> HDF5
>           // library take care about NULLTERM and NULLPAD strings
>           hsize_t size = H5Tget_size(type_id);
>           hid_t mem_type_id = H5Tcopy(H5T_C_S1);
>           H5Tset_size(mem_type_id, size);
>           value.resize(size, std::string::value_type());
>           H5Aread(attr_id, mem_type_id, &*value.begin());
>       }  else {
>           // read variable-length string, memory will be allocated
> by HDF5 C
>           // library and must be freed by us
>           char *c_str;
>           if (H5Aread(attr_id, H5T_C_S1, &c_str) >= 0) {
>               value = c_str;  // copy '\0'-terminated string
>               free(c_str);
>           }
>       }
>       H5Tclose(type_id);
>       H5Aclose(attr_id);
>       return value;
> }