How to take a screenshot of a specific area by coordinates?

Question

C++ / C#

There is a code that takes 4 handle coordinates.

void Window::getCoordinates() {
  RECT r;
  GetWindowRect(Window::pid.hWnd, &r);
  Window::coordinates[0] = r.bottom, Window::coordinates[1] = r.top;
  Window::coordinates[2] = r.right, Window::coordinates[3] = r.left;
}

You need to take a screenshot using 4 coordinates, so that later you can translate this screenshot into a file.