root@raspberrypi:/home/pi# g++ $(pkg-config --cflags opencv) rahul.cpp $(pkg-config --libs opencv) -o imagetest -lopencv_core -lopencv_video
/tmp/ccHalFfq.o: In function `main':
rahul.cpp:(.text+0xac): undefined reference to `cv::namedWindow(std::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, int)'
rahul.cpp:(.text+0xd4): undefined reference to `cv::VideoCapture::VideoCapture(int)'
rahul.cpp:(.text+0x158): undefined reference to `cv::imshow(std::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, cv::_InputArray const&)'
rahul.cpp:(.text+0x178): undefined reference to `cv::waitKey(int)'
rahul.cpp:(.text+0x19c): undefined reference to `cv::VideoCapture::isOpened() const'
rahul.cpp:(.text+0x1c8): undefined reference to `cv::VideoCapture::~VideoCapture()'
rahul.cpp:(.text+0x23c): undefined reference to `cv::VideoCapture::~VideoCapture()'
rahul.cpp:(.text+0x268): undefined reference to `vtable for cv::VideoCapture'
collect2: ld returned 1 exit status