problems in writing UTF8 strings when datatype is not given explicitly

[jkotan]

Running

#include <h5cpp/hdf5.hpp>
#include <h5cpp/datatype/string.hpp>
#include <h5cpp/datatype/types.hpp>


int main()
{
  using namespace hdf5;

  file::File f = file::create("myscan_test.nxs", file::AccessFlags::Truncate);

  node::Group root_group = f.root();

  // auto scalar_space = dataspace::Scalar();                                                                                                              
  // auto string_type = datatype::String::variable();                                                                                                      
  // string_type.encoding(datatype::CharacterEncoding::ASCII);                                                                                             

  // auto a = root_group.attributes.create("asciiattr", string_type, scalar_space);                                                                        
  // a.write("m");                                                                                                                                         


  auto scalar_space2 = dataspace::Scalar();
  auto string_type2 = datatype::String::variable();
  string_type2.encoding(datatype::CharacterEncoding::UTF8);

  auto a2 = root_group.attributes.create("utf8attr", string_type2, scalar_space2);
  // a2.write("um", string_type2);                                                                                                                         
  a2.write("um");
}

one get

HDF5-DIAG: Error detected in HDF5 (1.10.8) thread 1:
  #000: ../../../src/H5A.c line 614 in H5Awrite(): unable to write attribute
    major: Attribute
    minor: Write failed
  #001: ../../../src/H5Aint.c line 724 in H5A__write(): unable to convert between src and dst datatypes
    major: Attribute
    minor: Feature is unsupported
  #002: ../../../src/H5T.c line 4799 in H5T_path_find(): can't find datatype conversion path
    major: Datatype
    minor: Can't get value
  #003: ../../../src/H5T.c line 5021 in H5T__path_find_real(): no appropriate function for conversion path
    major: Datatype
    minor: Unable to initialize object
terminate called after throwing an instance of 'std::runtime_error'
  what():  Failure to write data to attribute!
Aborted

To make the above code working one can either uncomment a2.write("um", string_type2); or a block of instructions related to a.write("m") i.e. ASCII string

[jkotan]

similarly for datasets

#include <h5cpp/hdf5.hpp>
#include <h5cpp/datatype/string.hpp>
#include <h5cpp/datatype/types.hpp>


int main()
{
  using namespace hdf5;

  file::File f = file::create("myscan_test2.nxs", file::AccessFlags::Truncate);

  node::Group root_group = f.root();

  // auto scalar_space = dataspace::Scalar();                                                                                                
  // auto string_type = datatype::String::variable();                                                                                        
  // string_type.encoding(datatype::CharacterEncoding::ASCII);                                                                               

  //  auto dt = root_group.create_dataset("title",                                                                                           
  //                                  string_type,                                                                                           
  //                                  scalar_space);                                                                                         
  // dt.write("um");                                                                                                                         

  auto scalar_space2 = dataspace::Scalar();
  auto string_type2 = datatype::create<std::string>();
  string_type2.encoding(datatype::CharacterEncoding::UTF8);

  auto dt2 = root_group.create_dataset("title2",
                                      string_type2,
                                      scalar_space2);
  dt2.write("um");
}