Same API returned pointer pointed to diffent array location after printing.

Support
1

Hello,I have a code piece like blew to print same returned vtkDataArray twice:

	//get the normal of the representative cell
	auto normal = obj->cellNormals()->GetTuple(reprenstiveCell.id);

	std::cout << "Repre Cell Normals ---------- " << normal[0] << " " << normal[1] << " " << normal[3] << std::endl;

	for (int i = 0; i < obj->cellNormals()->GetNumberOfTuples(); i++)
	{
		auto n = obj->cellNormals()->GetTuple(i);
	}
	std::cout << "Repre Cell Normals ---------- " << normal[0] << " " << normal[1] << " " << normal[3] << std::endl;

And the printing result likes this:

Workspace 1_1562
Workspace 1_1562733×278 41.6 KB

As you can see,I have an item pointer which is returned by vtkDataArray->GetTuple(idx),in the first printing,it pointed to the “10st” item,after some operations like this:

	for (int i = 0; i < obj->cellNormals()->GetNumberOfTuples(); i++)
	{
		auto n = obj->cellNormals()->GetTuple(i);
	}

It points to “11th”,why would this happen? How to use the API returned pointer properly?

2

Methods like “n = obj->cellNormals()->GetTuple(i);” return temporary pointers to data, and are not thread-safe. They are holdovers from decades ago which, while convenient at times, are a dangerous programming practice and to be discouraged. Use alternative methods like “->GetTuple(i,n)” which copy data into n.