OpenCV program doesnt start the camera

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Hi, I recently installed ROS Electric, and now I'm trying to use OpenCV with it, I followed certain tutorials as this one Working with ROS and OpenCV (no sure if anyone else tried this too) ... Thing is, my built-in camera worked fine when i launch this .launch program:

<launch> <node name="uvc_cam_node" pkg="uvc_cam" type="uvc_cam_node" output="screen"> </node> </launch> (Refer to the part Test the launch script in the link above)

It does turn on, and writing this in terminal $ rosrun image_view image_view image:=/camera/image_raw I can see the image, but when I write my .cpp program for using OpenCV and I run it (refer to the part Write the code for image processing), my camera doesn't turn on, it doesnt show an error or anything it just stays there ... I have tried w another webcams and same thing happened. Does anyone have a clue why isn't running

Thanks