Cannot get OpenCV to compile because of undefined references?

I have tried all solutions. The -lopencv_core -lopencv_imgproc -lopencv_highgui in comments solved my problem. And now my command line looks like this in geany:

g++ -lopencv_core -lopencv_imgproc -lopencv_highgui  -o "%e" "%f"

When I build:

g++ -lopencv_core -lopencv_imgproc -lopencv_highgui  -o "opencv" "opencv.cpp" (in directory: /home/fedora/Desktop/Implementations)

The headers are:

#include "opencv2/imgproc/imgproc.hpp"
#include "opencv2/highgui/highgui.hpp"

This is a linker issue. Try:

g++ -o test_1 test_1.cpp `pkg-config opencv --cflags --libs`

This should work to compile the source. However, if you recently compiled OpenCV from source, you will meet linking issue in run-time, the library will not be found. In most cases, after compiling libraries from source, you need to do finally:

sudo ldconfig