OpenCV linking issue on BeagleBone Black and Ubuntu 12.04 (Precise Pangolin)

Question

I have BeagleBone Black with Ubuntu 12.04 (Precise Pangolin). I downloaded the OpenCV library from apt using the command:

sudo apt-get install -y libopencv-dev

This command installed required headers and libraries. Then I compiled my own program which is just showing a window with the following command:

gcc -I/usr/inlcude/ -I/usr/include/opencv2/ -L/usr/lib/ -lopencv_core -lopencv_highgui -lm opencv_test.c -o test

After some seconds it shows that it is unable to find a reference with 'lrint' and many more and at last showing the linking errors for cvNameWindow, cvShowImage, etc.

I think that this may be the problem of installed libraries. I downloaded the latest OpenCV Source, cross compiled the code provided on the OpenCV wiki with -DUSE_NEON=ON flags on my Ubuntu machine. I copied these headers and libraries into the extra partition which is ext4 formatted. Again I issued the follwing command:

gcc -I/usr/inlcude/ -I/media/misc/opencv/include/opencv/ -I/media/misc/opencv/include/ -L/usr/lib/ -L/media/misc/opencv/lib/ -lopencv_core -lopencv_highgui -lm opencv_test.c -o test

Note: /media/misc/ is the extra partition.

This command gives me the same output as earlier. Now I come to the point. Maybe I am not issuing the correct command.

Also I changed gcc to g++, and it gives me the errors like:

unable to find reference cvNamedWindow
unable to find reference cvShowImage

etc.

Answer 1

I accidentally compiled the sample code given in the OpenCV tarball, and that code compiled. Then I looked into the build script, and I found the following command:

g++ `pkg-config --cflags opencv` $1 -o $2 `pkg-config --libs opencv`

It is actually a script. $1 is the first argument, that is a .cpp file, and $2 is the second which is the output file. I use this script as follow:

./build_cv.sh opencv_test.cpp test

Note: make sure the script file "build_cv.sh" has execute permission. If not, then change its permission by typing:

chmod +x build_cv.sh

Now the problem. I was giving the location of header file and libraries in the first attempt. I have to give the location of headers before giving the source file, and location of the libraries after the output file. This is my experience; maybe some other guy have another way of compiling the code.

Answer 2

Your link command has: -lopencv_core -lopencv_highgui -lm opencv_test.c

This is the wrong order of arguments. To understand why, read this.

If I give this command to my existing ubuntu x82 machine, It compiles very nicely...

You mean "it links very nicely".

That's happening by coincidence, not because your link command is correct.