hid_t H5Aopen( hid_t obj_id, const char *attr_name, hid_t aapl_id )
will open your attribute. If you do something like
hid_t pizza = H5Aopen(file_id, "Attribute_name", H5P_DEFAULT)
pizza will be your attribute_id.
Im not sure either what the difference is between hdf5.h
and H5Cpp.h
. I think I have them both included, and it does not give an error. Maybe that helps too?