ITK  5.0.0
Insight Segmentation and Registration Toolkit
WikiExamples/Math/CovariantVector.cxx
int main(int, char*[])
{
v[0] = 1.0;
v[1] = 2.0;
v[2] = 3.0;
std::cout << "v: " << v << std::endl;
return EXIT_SUCCESS;
}