Import multiple data array from unstructured file into a polydata(cpp)

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I am a new user of VTK, everything is working before I get this problem. First, let me apologize for the dumb question I am asking here.
What I want to do is reading in an Unstructured dataset from a file, and put them into a vtkPolyData. So I wrote the following CPP code and it’s working, so far so good.
However, I have some other data other than ‘T’ and I want to put them into vtkPolyData once and for all.

    vtkSmartPointer<vtkPoints> vtk_points = reader->GetOutput()->GetPoints(); // coordinates
    // field data
    vtkSmartPointer<vtkPointData> vtk_point_data = reader->GetOutputAsDataSet()->GetPointData();
    vtk_point_data->Update();
    vtkSmartPointer<vtkDataArray> vtk_data_array = vtk_point_data->GetArray("T"); // read temperature
    // set value of the private member
    iPolyData = vtkSmartPointer<vtkPolyData>::New();
    iPolyData->SetPoints(vtk_points);  //set as original vector
    //todo: get multiple data array as inputs
    iPolyData->GetPointData()->SetScalars(vtk_data_array);
    iPolyData->GetPointData()->Update();

so I tried something like

iPolyData->GetPointData()->DeepCopy(reader->GetOutputAsDataSet()->GetPointData());
iPolyData->GetPointData()->Update();

this doesn’t work, as I am getting no output(actually I didn’t figure out how to debug other than see the output, how do I make gdb work for this, okay, that’s another confusion I have).

I also tried something like adding this array one by one. It doesn’t work as well.

vtkSmartPointer<vtkDataArray> vtk_data_array = vtk_point_data->GetArray("T"); // read temperature
iPolyData->GetPointData()->AddArray(vtk_data_array);
iPolyData->GetPointData()->Update();