root@raspberrypi:/home/pi# g++ rahul.cpp -o rahul `pkg-config --cflags --libs opencv`
/tmp/ccaIxwUW.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+0x144): undefined reference to `cv::_InputArray::_InputArray(cv::Mat const&)'
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'
/tmp/ccaIxwUW.o: In function `cv::Mat::~Mat()':
rahul.cpp:(.text._ZN2cv3MatD2Ev[_ZN2cv3MatD5Ev]+0x3c): undefined reference to `cv::fastFree(void*)'
/tmp/ccaIxwUW.o: In function `cv::Mat::release()':
rahul.cpp:(.text._ZN2cv3Mat7releaseEv[cv::Mat::release()]+0x58): undefined reference to `cv::Mat::deallocate()'
collect2: ld returned 1 exit status