Write two cubes to a VTP file

#include <vtkCubeSource.h>
 
 
void WriteTwoCubes(const string &OutputFilename)
{
	vtkSmartPointer<vtkCubeSource> Cube1 = vtkSmartPointer<vtkCubeSource>::New();
	Cube1->SetCenter(0.0, 0.0, 0.0);
	Cube1->SetXLength(.5);
	Cube1->SetYLength(.5);
	Cube1->SetZLength(.5);
 
	vtkSmartPointer<vtkCubeSource> Cube2 = vtkSmartPointer<vtkCubeSource>::New();
	Cube2->SetCenter(5.0, 0.0, 0.0);
	Cube2->SetXLength(.5);
	Cube2->SetYLength(.5);
	Cube2->SetZLength(.5);
 
	vtkSmartPointer<vtkPolyData> polydata1 = Cube1->GetOutput();
	vtkSmartPointer<vtkPolyData> polydata2 = Cube2->GetOutput();
 
	vtkSmartPointer<vtkAppendPolyData> CombinedData = vtkSmartPointer<vtkAppendPolyData>::New();;
	CombinedData->AddInput(polydata1);
	CombinedData->AddInput(polydata2);
 
	//write the file
	vtkSmartPointer<vtkXMLPolyDataWriter> writer = vtkSmartPointer<vtkXMLPolyDataWriter>::New();
	writer->SetInput(CombinedData->GetOutput());
 
	writer->SetFileName(OutputFilename.c_str());
	writer->Write();
 
}