Creating a Group

What is a Group?

An HDF5 group is a structure containing zero or more HDF5 objects. The two primary HDF5 objects are groups and datasets. To create a group, the calling program must:

1. Obtain the location identifier where the group is to be created.
2. Create the group.
3. Close the group.

C:

  group_id = H5Gcreate (loc_id, name, size_hint);
  status = H5Gclose (group_id);

  CALL h5gcreate_f (loc_id, name, group_id, error, size_hint=size)
       or
  CALL h5gcreate_f (loc_id, name, group_id, error)


  CALL h5gclose_f (group_id, error)

Programming Example

Description

Remarks

• H5Gcreate/h5gcreate_f creates a new empty group, named MyGroup and located in the root group, and returns a group identifier.

  C:

    hid_t H5Gcreate (hid_t loc_id, const char *name, size_t size_hint) 
  

  FORTRAN:

    h5gcreate_f (loc_id, name, group_id, hdferr, size_hint)
  
             loc_id     INTEGER(HID_T)
             name       CHARACTER(LEN=*)
             group_id   INTEGER(HID_T)
             hdferr     INTEGER
                        (Possible values: 0 on success and -1 on failure)
             size_hint  INTEGER(SIZE_T), OPTIONAL
                        (Default value: OBJECT_NAMELEN_DEFAULT_F)
           
  

  • The loc_id parameter specifies the location at which to create the group.

  • The name parameter specifies the name of the group to be created.

  • The size_hint parameter specifies how much file space to reserve to store the names that will appear in the group. If a non-positive value is supplied, then a default size is used. Passing a value of zero is usually adequate since the library is able to dynamically resize the name heap.

  • In FORTRAN, the return value for the routine is passed in hdferr: 0 if successful, -1 otherwise. The group identifier is passed back in group_id. In C, the function returns a valid group identifier if successful and a negative value otherwise.

• H5Gclose/h5gclose_f closes the group. This call is mandatory.

  C:

    herr_t H5Gclose (hid_t group_id) 
  

  FORTRAN:

    h5gclose_f (group_id, hdferr)
  
             group_id  INTEGER(HID_T)
             hdferr    INTEGER
                       (Possible values: 0 on success and -1 on failure)
           
  

File Contents

Fig. 8.1   The Contents of group.h5.		Fig. 8.2   group.h5 in DDL
		HDF5 "group.h5" { GROUP "/" { GROUP "MyGroup" { } } }