一台相机上的多个视频贴

我可能有一个以上的视频摄像机。不幸的是，有时与相机的连接似乎被终止。

示例：

Mat img;
VideoCapture v1(0);
v1.read(img);      //img is a valid picture
VideoCapture v2(0);
v1.read(img);      //img is a valid picture
v2.read(img);      //img is a valid picture
v2 = v1;
v2.read(img);      //img is not a valid picture. Connection seems to be closed

这是正确的行为，还是OpenCV中的错误？

有没有办法检查特定的deviceNumber是否已经打开并获得负责任的类？

伪代码：

Mat img;
VideoCapture v1(0);
VideoCapture v2 = alreadyOpen(0);
alreadyOpen(0){
    if(VideoCapture(0).isOpen()){ //how do i check that
        return "v1"               //how do i know where v1 is
    }else{
        return VideoCapture(0);
    }
}