A problem in saving "long double" variables to hdf5 file - c++

Question

I'm new to hdf5. I'm trying to save the results of a simulation in hdf5 file. The variables are long double. So, I mapped them into NATIVE_LDOUBLE. However, the saved values are completely wrong (fluctuating between very small and very large values).
When I save them with NATIVE_DOUBLE, everything is ok. But I need to save long double.
My question is how to properly save long double variables, and moreover quadruple precision variables?
I deeply appreciate your help. Examples are also appreciated.
here is the code
void createHDF5_2DProjectionFile(char* file_name,
CarGrid1D3V<long double>& ph_grid,
std::string first_dim,
std::string second_dim,
long double *x1, int size_x1,
long double *x2, int size_x2)
{
try
{
/* define the size of the datasets containing the coordinates x1
and x2
*/
PredType h5Int = PredType::NATIVE_INT;
PredType h5DoubleL = PredType::NATIVE_LDOUBLE;
PredType h5Double = PredType::NATIVE_DOUBLE;
/* Define the parameters of grid space
DS --> Data Space
*/
hsize_t x1_dims[1], x2_dims[1];
x1_dims[0] = size_x1;
x2_dims[0] = size_x2;
H5File *file_id = new H5File(file_name, H5F_ACC_TRUNC);
/* Saving string attribute
Create dataspace with H5S_SCALAR
Create string datatype of specific length of characters
Create attribute and write to it
*/
DataSpace attr_stringDS = DataSpace(H5S_SCALAR);
StrType strdatatype(PredType::C_S1, 64);
Attribute original_DistFun = file_id->createAttribute("/OriginalDistFun",
strdatatype, attr_stringDS);
original_DistFun.write(strdatatype, "1D3V");
Attribute projection = file_id->createAttribute("/Projection",
strdatatype, attr_stringDS);
projection.write(strdatatype, first_dim + " - " + second_dim);
/* Create the data spaces for grid points along each direction */
DataSpace* first_dimDS_id = new DataSpace(1, x1_dims, NULL);
DataSpace* second_dimDS_id = new DataSpace(1, x2_dims, NULL);
/* Create and fille the datasets for grid points along each direction */
DataSet *data_dim1 = new DataSet(file_id->createDataSet(first_dim,
h5DoubleL, *first_dimDS_id));
data_dim1->write(x1, h5DoubleL);
DataSet *data_dim2 = new DataSet(file_id->createDataSet(second_dim,
h5DoubleL, *second_dimDS_id));
data_dim2->write(x2, h5DoubleL);
/* Important attributes added to the file */
long double x_minmax[2], px_minmax[2],
py_minmax[2], pz_minmax[2], mom_steps[3],
ph_vols[3], spatial_steps[1];
x_minmax[0] = ph_grid.x_min_;
x_minmax[1] = ph_grid.x_max_;
px_minmax[0] = ph_grid.px_min_;
px_minmax[1] = ph_grid.px_max_;
py_minmax[0] = ph_grid.py_min_;
py_minmax[1] = ph_grid.py_max_;
pz_minmax[0] = ph_grid.pz_min_;
pz_minmax[1] = ph_grid.pz_max_;
mom_steps[0] = ph_grid.dpx_;
mom_steps[1] = ph_grid.dpy_;
mom_steps[2] = ph_grid.dpz_;
ph_vols[0] = ph_grid.dvs_;
ph_vols[1] = ph_grid.dvp_;
ph_vols[2] = ph_grid.dv_;
spatial_steps[0] = ph_grid.dx_;
ph_grid.print_characteristics();
std::cout << x_minmax[0] << " , " << x_minmax[1] << "\n";
/* define attributes configuration */
hsize_t space_1[1];
space_1[0] = 1;
hsize_t space_2[1];
space_2[0] = 2;
hsize_t space_3[1];
space_3[0] = 3;
DataSpace attr_space_1 = DataSpace(1, space_1);
DataSpace attr_space_2 = DataSpace(1, space_2);
DataSpace attr_space_3 = DataSpace(1, space_3);
Attribute x_interval = file_id->createAttribute("[x_min,x_max]",
h5DoubleL, attr_space_2);
x_interval.write(h5DoubleL, x_minmax);
Attribute px_interval = file_id->createAttribute("[px_min,px_max]",
h5DoubleL, attr_space_2);
px_interval.write(h5DoubleL, px_minmax);
Attribute py_interval = file_id->createAttribute("[py_min,py_max]",
h5DoubleL, attr_space_2);
py_interval.write(h5DoubleL, py_minmax);
Attribute pz_interval = file_id->createAttribute("[pz_min,pz_max]",
h5DoubleL, attr_space_2);
pz_interval.write(h5DoubleL, pz_minmax);
Attribute MomVolumes = file_id->createAttribute("[dpx,dpy,dpz]",
h5DoubleL, attr_space_3);
MomVolumes.write(h5DoubleL, mom_steps);
Attribute PhVolumes = file_id->createAttribute("[dv_s, dv_m, dv_t]",
h5DoubleL, attr_space_3);
PhVolumes.write(h5DoubleL, ph_vols);
Attribute SpatialVolumes = file_id->createAttribute("[dx]", PredType::NATIVE_DOUBLE,
attr_space_1);
SpatialVolumes.write(h5DoubleL, spatial_steps);
/* Free memory */
delete data_dim1;
delete data_dim2;
delete first_dimDS_id;
delete second_dimDS_id;
delete file_id;
}
catch(DataSetIException error)
{
error.printErrorStack();
}
catch(DataSpaceIException error)
{
error.printErrorStack();
}
catch(FileIException error)
{
error.printErrorStack();
}
}
Update
A great discussion and explanations are available on HDF5 forum where I posted the same question
https://forum.hdfgroup.org/t/a-problem-when-saving-native-ldouble-variables/9504
Also, Steven Varga provided examples to answer this question on his GitHub by constructing a user-defined datatype (see this link).