using gcc to link libraries and to include headers

savio · 07-16-2015, 07:04 AM

Hi,

I am writing a program using opencv calls and I want to compile it and make the executable.
I already read the gcc tutorial but I would like to know how to link opencv libraries I am using.
My current command to compile is the following:

Code:

gcc -I/home/myname/opencv-3.0.0/include/opencv -L/home/myname/opencv-3.0.0/cmake_binary_dir/lib -lopencv_core -lopencv_highgui -lopencv_imgproc program.c -o program

It doesn't work.
What is wrong with that?

Thanks in advance for help

millgates · 07-16-2015, 07:16 AM

What does "It doesn't work" mean?
Any error messages?
What is your distribution and gcc version?

savio · 07-16-2015, 08:08 AM

I tried in two ways:

Code:

savio@savio-R580:~/programmi$ gcc -I/home/savio/opencv-3.0.0/include/opencv -L/home/savio/opencv-3.0.0/cmake_binary_dir/lib -llibopencv_core -llibopencv_highgui -llibopencv_imgproc imagefilter.c -o imagefilter
/usr/bin/ld: impossibile trovare -llibopencv_core
/usr/bin/ld: impossibile trovare -llibopencv_highgui
/usr/bin/ld: impossibile trovare -llibopencv_imgproc
collect2: error: ld returned 1 exit status

and

Code:

savio@savio-R580:~/programmi$ gcc -I/home/savio/opencv-3.0.0/include/opencv -L/home/savio/opencv-3.0.0/cmake_binary_dir/lib -lopencv_core -lopencv_highgui -lopencv_imgproc imagefilter.c -o imagefilter
/tmp/ccDUEgAk.o: nella funzione "cvDecRefData":
imagefilter.c:(.text+0xa6a): riferimento non definito a "cvFree_"
imagefilter.c:(.text+0xaf2): riferimento non definito a "cvFree_"
/tmp/ccDUEgAk.o: nella funzione "cvGetRow":
imagefilter.c:(.text+0xc08): riferimento non definito a "cvGetRows"
/tmp/ccDUEgAk.o: nella funzione "cvGetCol":
imagefilter.c:(.text+0xc36): riferimento non definito a "cvGetCols"
/tmp/ccDUEgAk.o: nella funzione "cvReleaseMatND":
imagefilter.c:(.text+0xc50): riferimento non definito a "cvReleaseMat"
/tmp/ccDUEgAk.o: nella funzione "cvSubS":
imagefilter.c:(.text+0xdac): riferimento non definito a "cvAddS"
/tmp/ccDUEgAk.o: nella funzione "cvCloneSeq":
imagefilter.c:(.text+0xde5): riferimento non definito a "cvSeqSlice"
/tmp/ccDUEgAk.o: nella funzione "cvSetNew":
imagefilter.c:(.text+0xe52): riferimento non definito a "cvSetAdd"
/tmp/ccDUEgAk.o: nella funzione "cvGetSetElem":
imagefilter.c:(.text+0xefa): riferimento non definito a "cvGetSeqElem"
/tmp/ccDUEgAk.o: nella funzione "cvReadIntByName":
imagefilter.c:(.text+0xfa9): riferimento non definito a "cvGetFileNodeByName"
/tmp/ccDUEgAk.o: nella funzione "cvReadRealByName":
imagefilter.c:(.text+0x1053): riferimento non definito a "cvGetFileNodeByName"
/tmp/ccDUEgAk.o: nella funzione "cvReadStringByName":
imagefilter.c:(.text+0x10e6): riferimento non definito a "cvGetFileNodeByName"
/tmp/ccDUEgAk.o: nella funzione "cvReadByName":
imagefilter.c:(.text+0x1126): riferimento non definito a "cvGetFileNodeByName"
imagefilter.c:(.text+0x113c): riferimento non definito a "cvRead"
/tmp/ccDUEgAk.o: nella funzione "cvContourPerimeter":
imagefilter.c:(.text+0x1170): riferimento non definito a "cvArcLength"
/tmp/ccDUEgAk.o: nella funzione "cvCalcHist":
imagefilter.c:(.text+0x11b2): riferimento non definito a "cvCalcArrHist"
/tmp/ccDUEgAk.o: nella funzione "cvEllipseBox":
imagefilter.c:(.text+0x127e): riferimento non definito a "cvEllipse"
/tmp/ccDUEgAk.o: nella funzione "cvFont":
imagefilter.c:(.text+0x12c8): riferimento non definito a "cvInitFont"
/tmp/ccDUEgAk.o: nella funzione "main":
imagefilter.c:(.text+0x1396): riferimento non definito a "cvLoadImage"
imagefilter.c:(.text+0x13af): riferimento non definito a "cvGetSize"
imagefilter.c:(.text+0x13c1): riferimento non definito a "cvCreateImage"
imagefilter.c:(.text+0x13ed): riferimento non definito a "cvSmooth"
imagefilter.c:(.text+0x1403): riferimento non definito a "cvSaveImage"
imagefilter.c:(.text+0x141b): riferimento non definito a "cvReleaseImage"
imagefilter.c:(.text+0x1427): riferimento non definito a "cvReleaseImage"
collect2: error: ld returned 1 exit status

How sould I correctly specify the libraries?

NevemTeve · 07-16-2015, 08:08 AM

You don't have to save line-breaks, use them generously:

Code:

gcc -I/home/myname/opencv-3.0.0/include/opencv \
    -L/home/myname/opencv-3.0.0/cmake_binary_dir/lib \
    -lopencv_core -lopencv_highgui -lopencv_imgproc program.c -o program

That 'cmake_binary_dir' doesn't sound plausible... Try this:

Code:

find /home/myname/opencv-3.0.0 -name 'libopencv_core*'

PS: unset LC_ALL in this moment. Translated error messages are unusable!

savio · 07-16-2015, 08:10 AM

I compiled and installed opencv sources by myself, specifying that directory:

Code:

savio@savio-R580:~/programmi$ find /home/savio/opencv-3.0.0 -iname 'libopencv_core*'
/home/savio/opencv-3.0.0/cmake_binary_dir/lib/libopencv_core.so.3.0
/home/savio/opencv-3.0.0/cmake_binary_dir/lib/libopencv_core.so
/home/savio/opencv-3.0.0/cmake_binary_dir/lib/libopencv_core_pch_dephelp.a
/home/savio/opencv-3.0.0/cmake_binary_dir/lib/libopencv_core.so.3.0.0

NevemTeve · 07-16-2015, 08:14 AM

In your case it is:

Code:

find /home/savio/opencv-3.0.0 -iname 'libopencv_core*'

savio · 07-16-2015, 08:17 AM

Code:

savio@savio-R580:~/programmi$ find /home/savio/opencv-3.0.0 -name 'libopencv_core*'
/home/savio/opencv-3.0.0/cmake_binary_dir/lib/libopencv_core.so.3.0
/home/savio/opencv-3.0.0/cmake_binary_dir/lib/libopencv_core.so
/home/savio/opencv-3.0.0/cmake_binary_dir/lib/libopencv_core_pch_dephelp.a
/home/savio/opencv-3.0.0/cmake_binary_dir/lib/libopencv_core.so.3.0.0

NevemTeve · 07-16-2015, 08:29 AM

(Just for fun I tried to download this piece of shi^H^H^H software, but it is bigger that the linux kernel..)

millgates · 07-16-2015, 08:51 AM

Also, the recent versions of gcc in some distros seem to have stricter rules concerning the order in which the objects are specified to the linker. The order of the objects should correspond to the way they depend on each other.
So, imagefilter.c should go first, before all the libraries because it uses symbols defined in those libraries, and so on. I don't know how the so files from OpenCV depend on each other (use ldd to find out), but an object that uses something should always go before the object that provides it.

savio · 07-16-2015, 09:02 AM

It is a bit better but still it doesn't work:

Code:

savio@savio-R580:~/programmi$ gcc imagefilter.c -o imagefilter -I/home/savio/opencv-3.0.0/include/opencv -L/home/savio/opencv-3.0.0/cmake_binary_dir/lib -lopencv_core -lopencv_highgui -lopencv_imgproc
/tmp/ccmZzYQz.o: nella funzione "main":
imagefilter.c:(.text+0x1396): riferimento non definito a "cvLoadImage"
imagefilter.c:(.text+0x1403): riferimento non definito a "cvSaveImage"
collect2: error: ld returned 1 exit status

NevemTeve · 07-16-2015, 09:09 AM

If you're lucky, you have a *.pc file somewhere:

Code:

find ~/opencv-3.0.0 -name '*.pc'

savio · 07-16-2015, 09:13 AM

I found dependencies using ldd command.
Now it compiles but not corretly:

Code:

savio@savio-R580:~/programmi$ gcc imagefilter.c -o imagefilter -I/home/savio/opencv-3.0.0/include/opencv -L/home/savio/opencv-3.0.0/cmake_binary_dir/lib -lopencv_imgcodecs -lopencv_imgproc -lopencv_core -lopencv_highgui
savio@savio-R580:~/programmi$ ./imagefilter lena_noise.BMP 
./imagefilter: error while loading shared libraries: libopencv_imgcodecs.so.3.0: cannot open shared object file: No such file or directory

There is the .pc file:

Code:

savio@savio-R580:~/programmi$ find ~/opencv-3.0.0 -name '*.pc'
/home/savio/opencv-3.0.0/cmake_binary_dir/unix-install/opencv.pc

Anyway, looking at opencv.pc file, I tried also modifying the gcc command parameters like this:

Code:

savio@savio-R580:~/programmi$ gcc imagefilter.c -o imagefilter -I/usr/local/include -L/usr/local/lib -lopencv_imgcodecs -lopencv_imgproc -lopencv_highgui -lopencv_core
savio@savio-R580:~/programmi$ ./imagefilter lena_noise.BMP 
./imagefilter: error while loading shared libraries: libopencv_imgcodecs.so.3.0: cannot open shared object file: No such file or directory

but I have exactly the same problem.

millgates · 07-16-2015, 10:09 AM

Try running the program with

Code:

LD_LIBRARY_PATH=/home/savio/opencv-3.0.0/cmake_binary_dir/lib:$LD_LIBRARY_PATH ./imagefilter lena_noise.BMP

NevemTeve · 07-16-2015, 10:13 AM

Cool!

So try this:

Code:

export PKG_CONFIG_PATH="/home/savio/opencv-3.0.0/cmake_binary_dir/unix-install:$PKG_CONFIG_PATH"

gcc $(pkg-config --cflags opencv) imagefilter.c \
    -o imagefilter $(pkg-config --libs opencv)