Hi Martin.
On Fri, Apr 08, 2011 at 02:59:59PM +0100, Martin Galpin wrote:
> I am not using a "blob" and indeed using a H5T_COMPOUND type that is
> built using the constituents of the structure.
>
> So, in the case of:
>
> // C
> struct A
> {
> int x;
> int y;
> };
>
> struct Container
> {
> int offset;
> struct A element;
> }
>
> It would be:
>
> H5insert... H5T_NATIVE_INT32, H5T_NATIVE_INT32, H5T_NATIVE_INT32 (offset, x,
> y).
Not really sure what this means;-) If this is the in-memory layout
then it might just be working because in this case the in-memory
layout of the structure is really that simple, i.e. just three
ints, one after another. I wouldn't like to bet that it is that
simple in all possible cases... BTW, if this is really about the
in-memory layout, why are you using 'H5T_NATIVE_INT32' instead of
'H5T_NATIVE_INT'?
> With this approach I can H5PTappend a Container* packet directly to
> the compound type. Should I be creating nested compound types for the
> nested structures?
If you want to retain the nested-ness of the structure in the
HDF file then I would say yes, definitely. To simplify the dis-
cussion I wrote a shot program that just writes out a single
instance of your nested structure and then reading it back in:
--------8<----------------------------------
#include <stdio.h>
#include <hdf5.h>
typedef struct A
{
int x;
int y;
} A_t;
typedef struct Container
{
int offset;
A_t element;
} Container_t;
int
main( )
{
Container_t s = { 16, { 19, -21 } };
hid_t file,
space,
dset,
A_filetype,
A_memtype,
C_filetype,
C_memtype;
hsize_t dims[ 1 ] = { 1 };
int ndims;
/* Print out the original contents of the structure */
printf( "Before: { %d, { %d, %d } }\n",
s.offset, s.element.x, s.element.y );
/* Create data type with in-memory layout of the A structure */
A_memtype = H5Tcreate( H5T_COMPOUND, sizeof( A_t ) );
H5Tinsert( A_memtype, "x", HOFFSET( A_t, x ), H5T_NATIVE_INT );
H5Tinsert( A_memtype, "y", HOFFSET( A_t, y ), H5T_NATIVE_INT );
/* Create data type with in-memory layout of the Container structure */
C_memtype = H5Tcreate( H5T_COMPOUND, sizeof( Container_t ) );
H5Tinsert( C_memtype, "offset", HOFFSET( Container_t, offset ),
H5T_NATIVE_INT );
H5Tinsert( C_memtype, "element", HOFFSET( Container_t, element ),
A_memtype );
/* Create data type with in-file layout of the A structure */
A_filetype = H5Tcreate( H5T_COMPOUND, 2 * H5Tget_size( H5T_NATIVE_INT32 ) );
H5Tinsert( A_filetype, "x", 0, H5T_NATIVE_INT32 );
H5Tinsert( A_filetype, "y", H5Tget_size( H5T_NATIVE_INT32 ),
H5T_NATIVE_INT32 );
/* Create data type with in-file layout of the Container structure */
C_filetype = H5Tcreate( H5T_COMPOUND,
H5Tget_size( H5T_NATIVE_INT32 )
+ H5Tget_size( A_filetype ) );
H5Tinsert( C_filetype, "offset", 0, H5T_NATIVE_INT32 );
H5Tinsert( C_filetype, "element", H5Tget_size( H5T_NATIVE_INT32 ),
A_filetype );
/* Open a file for writing */
file = H5Fcreate( "ctest.h5", H5F_ACC_TRUNC, H5P_DEFAULT, H5P_DEFAULT );
/* Create a dataspace and the dataset */
space = H5Screate_simple( 1, dims, NULL );
dset = H5Dcreate2( file, "test set", C_filetype, space,
H5P_DEFAULT, H5P_DEFAULT, H5P_DEFAULT );
/* Write the structure out */
H5Dwrite( dset, C_memtype, H5S_ALL, H5S_ALL, H5P_DEFAULT, &s );
/* Get rid of resources and close the file */
H5Dclose( dset );
H5Sclose( space );
H5Tclose( C_filetype );
H5Tclose( A_filetype );
H5Fclose( file );
/* Clear out the structure and print it to show it's all 0 now */
s.offset = s.element.x = s.element.y = 0;
printf( "After clear: { %d, { %d, %d } }\n",
s.offset, s.element.x, s.element.y );
/* Now the reverse (re-using the in-memory layout of the structure,
the in-file layout is in the file, so it doesn't need to be re-
created) */
file = H5Fopen( "ctest.h5", H5F_ACC_RDONLY, H5P_DEFAULT );
dset = H5Dopen2( file, "test set", H5P_DEFAULT );
space = H5Dget_space( dset );
ndims = H5Sget_simple_extent_dims( space, dims, NULL );
H5Dread( dset, C_memtype, H5S_ALL, H5S_ALL, H5P_DEFAULT, &s );
H5Dclose( dset );
H5Sclose( space );
H5Tclose( C_memtype );
H5Tclose( A_memtype );
H5Fclose( file );
/* Show that the structure again contains the original data */
printf( "Finally: { %d, { %d, %d } }\n",
s.offset, s.element.x, s.element.y );
return 0;
}
--------8<----------------------------------
Please keep in mind that this was my first attempt at trying to
deal with compounds containing compounds, so there might be some
bugs lurking...
Best regards, Jens
--
\ Jens Thoms Toerring ________ [email protected]
\_______________________________ http://toerring.de
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