Cookbook : Attributes

String Attributes

This snippet reads the value from an attribute attached to the specified objectId.

    private bool ReadStringAttribute(hid_t objectId, string title, out string value)
    {
      value = "";

      hid_t attributeId = 0;
      hid_t typeId = 0;

      try
      {
        attributeId = H5A.open(objectId, title);
        typeId = H5A.get_type(attributeId);
        var sizeData = H5T.get_size(typeId);
        var size = sizeData.ToInt32();
        byte[] strBuffer = new byte[size];

        var aTypeMem = H5T.get_native_type(typeId, H5T.direction_t.ASCEND);
        GCHandle pinnedArray = GCHandle.Alloc(strBuffer, GCHandleType.Pinned);
        H5A.read(attributeId, aTypeMem, pinnedArray.AddrOfPinnedObject());
        pinnedArray.Free();
        H5T.close(aTypeMem);

        value = System.Text.ASCIIEncoding.ASCII.GetString(strBuffer);

        return true;
      }
      catch (Exception ex)
      {
        return false;
      }
      finally
      {
        if (attributeId != null) H5A.close(attributeId);
        if (typeId != null) H5T.close(typeId);
      }
    }

Here we create an attribute attached to the given objectId:

    private bool CreateStringAttribute(hid_t objectId, string title, string description)
    {
      hid_t attributeSpace = 0;
      hid_t stringId = 0;
      hid_t attributeId = 0;

      try
      {
        attributeSpace = H5S.create(H5S.class_t.SCALAR);
        stringId = H5T.copy(H5T.C_S1);
        H5T.set_size(stringId, new IntPtr(description.Length));
        attributeId = H5A.create(objectId, title, stringId, attributeSpace);

        IntPtr descriptionArray = Marshal.StringToHGlobalAnsi(description);
        H5A.write(attributeId, stringId, descriptionArray);

        Marshal.FreeHGlobal(descriptionArray);

        return true;
      }
      catch (Exception ex)
      {
        return false;
      }
      finally
      {
        if (attributeId != 0) H5A.close(attributeId);
        if (stringId != 0) H5T.close(stringId);
        if (attributeSpace != 0) H5S.close(attributeSpace);
      }
    }