String not written out to Compound datatype


Hi, Sorry if this is the wrong place to ask this, however I’m stuck on this problem of not being able to write out a string to a compound datatype: Code is:

    hid_t      memtype;

    const int  LENGTH = 2;
    const int  RANK = 1;
    int        i;
    hid_t      file, dataset, space, strtype; // Handles 
    herr_t     str;
    hsize_t    dim[] = { LENGTH };   // Dataspace dimensions 

    //Create the data space.
    space = H5Screate_simple(RANK, dim, NULL);

    //Create variable - length string datatype.
    strtype = H5Tcopy(H5T_C_S1);
    str = H5Tset_size(strtype, H5T_C_S1);
    H5::StrType stype(H5::PredType::C_S1, H5T_VARIABLE);
    //H5::StrType(H5::PredType::C_S1, H5T_VARIABLE)

    memtype = H5Tcreate(H5T_COMPOUND, sizeof(entity_data));
    H5Tinsert(memtype, "name", HOFFSET(Entity, name), strtype);
    H5Tinsert(memtype, "entityID", HOFFSET(Entity, entity_id), H5T_NATIVE_INT);
    H5Tinsert(memtype, "parentID", HOFFSET(Entity, parent_id), H5T_NATIVE_INT);

    //Create the dataset.
    dataset = H5Dcreate2(mEntGrpPtr->getLocId(), "EntityData", memtype, space, H5P_DEFAULT, H5P_DEFAULT, H5P_DEFAULT);
    //Wtite data to the dataset;
     H5Dwrite(dataset, memtype, H5S_ALL, H5S_ALL, H5P_DEFAULT, &entity_data);

The file output is:

GROUP “Entities” {
DATASET “EntityData” {
H5T_STD_I32LE “entityID”;
H5T_STD_I32LE “parentID”;
DATASPACE SIMPLE { ( 2 ) / ( 2 ) }
(0): {
(1): {

What am I missing?

All the best,


Paul, can you show us the definition of entity_data's (Entity?) type? What’s the type of the name field? Why are you mixing two APIs? (What’s the point of H5::StrType?) G.


Hi, thanks for the reply.

my struct looks like this

typedef struct Entity
char name[36];

int    entity_id;

int    parent_id;

} Entity;

At the moment I’m trying to use fixed length strings. with char [36].
I’m copying the string values with:


My current setup is

hid_t dtype = H5Tcopy(H5T_C_S1);
int size = 36;
status = H5Tset_size(dtype, size);

memtype = H5Tcreate(H5T_COMPOUND, sizeof(Entity));
status = H5Tinsert(memtype, “entityID”, HOFFSET(Entity, entity_id), H5T_NATIVE_INT);
status = H5Tinsert(memtype, “name”, HOFFSET(Entity, name), dtype);
status = H5Tinsert(memtype, “parentID”, HOFFSET(Entity, parent_id), H5T_NATIVE_INT);

space = H5Screate_simple(1, dims, NULL);

H5std_string dsetName = “Entity” + std::to_string(entity_data.entity_id);

dset = H5Dcreate(mEntGrpPtr->getLocId(), dsetName.c_str(), memtype, space, H5P_DEFAULT, H5P_DEFAULT, H5P_DEFAULT);
status = H5Dwrite(dset, memtype, H5S_ALL, H5S_ALL, H5P_DEFAULT, &entity_data);

II’m getting this in the h5 file:

entityID name parentID
1601463658 b’\x01’ 0

when it should be:

entityID name parentID
0 1 jet 0

If I try to setup for variable strings my application crashes.
I’m new to hdf5 and I know I’m setting up the mem space wrong, just need a little help…

Best regards,


Hi, I fixed it. It was more to do with the way I was creating/copying over strings.