An example of how to properly define the vlen type in the fortran
call for exactly the data structure as in the C example would clarify
it.
Thanks!
-Roy
On Apr 17, 2008, at 6:40 PM, Unidata netCDF Support wrote:
On Apr 10, 2008, at 10:52 AM, Unidata netCDF Support wrote:
Hi All:
I am working on creating a netcdf4 file with the structure we are
trying to achieve. I have a file with Box10 groups and B0x2
subgroups, works great. Now I am trying to do ragged arrays.
Below
is the only fortran example I can find that does ragged arrays. It
is only writing one,1-dimensional array, so I am unsure what I do
when I am writing an N-dimensional ragged array. Do I just write
each "column" in a loop - if so how does it know that it is writing
to the same structure? Or if I can do multiple "columns" at once,
Howdy Roy!
To answer some more of your questions, you define your vlen type,
and then create a variable of that type, with whatever dimensions
you want, 1D, 2D, 3D, whatever.
Then you call the nf_put_vara() and nf_get_vara() functions to
write and read the data. You give them the address of the array of
data, whether in fortran or C.
If your fortran compiler's memory map of the data are the same as
the C version, everything will just work.
There is one caveat: this is untested. I have never tried this from
fortran.
There is one twist: you must free each VLEN separately or you will
have memory leaks. There is a function nf_free_vlen() for this.
how do I set that up. More realistic examples would be very
helpful,
including an example that writes an N-dimensional ragged array, and
an example that adds one more column to an existing ragged array.
Even just the fortran equivalent of the program tst_vl.c would be
very helpful
I agree with you that there needs to be a realistic example, but my
experience is that even more necessary are some basic tests. The
fortran version of tst_vl.c, as you say. We are not there yet...
I will add some tests for this after my upcoming beta2 release
(which will happen any day now). As for the scientifically
realistic example, well, perhaps we should be asking you for that! ;-)
It is clear how to do it in C (I set up an array of structures
of the
given form), but not in either version of FORTRAN.
It works like this: the f77 layer is just the a bunch of C wrapper
shells around the C API functions, with a little macro magic to
convert C-like 0-based indexes into F77-like 1-based indexes, and
to reorder dimensions so that the first C dimension will come last,
etc.
Then the F90 API is built right on top of those F77 calls. Just
look at the F90 code and you will see that most of the functions
are just F90 wrappers around the F77 function.
It is the same in Fortran as C, except that the HDF5 build knows
about the C structs, but not about the fortran structs. So it
guarantees to work from C, but not from fortran. However, if
fortran uses the same layout for the data in memory as the C
compiler does (including any rules for padding or boundaries, or
whatever), then everything will work. (Because everything is
happening at the C layer anyway.)
But the code will not be portable, because if another fortran
compiler does something different, the data will not look the same
in memory.
(This portability problem does not matter once the data are
written. HDF5 uses a known system of storage, which is always the
same, no matter what platform you are on. So once you get the data
into the HDF5 file, it is portable. It's just the code that gets
the data into the file is not portable.)
Does this shed any light on your problem space?
Thanks!
Ed
Ticket Details
===================
Ticket ID: KJX-899747
Department: Support netCDF
Priority: Normal
Status: Open
**********************
"The contents of this message do not reflect any position of the U.S.
Government or NOAA."
**********************
Roy Mendelssohn
Supervisory Operations Research Analyst
NOAA/NMFS
Environmental Research Division
Southwest Fisheries Science Center
1352 Lighthouse Avenue
Pacific Grove, CA 93950-2097
e-mail: Roy.Mendelssohn@xxxxxxxx (Note new e-mail address)
voice: (831)-648-9029
fax: (831)-648-8440
www: http://www.pfeg.noaa.gov/
"Old age and treachery will overcome youth and skill."
