// Example program
#include <iostream>
#include <vector>
namespace cv {
struct Point {
int x;
int y;
};
}
int main()
{
std::vector<std::vector<cv::Point> > contours3 {{{1,2},{3,4},{5,6}}};
contours3[0]; // std::vector<cv:::Point>
contours3[0][0]; // cv::Point
int x = contours3[0][0].x; // int (cv::Point::value_type)
std::cout << x << '\n';
}