OpenCV undefined reference to - c++

Question

I'm using Ubuntu 16.04 and OpenCV 2.4.9 and my quite simple example programs are constantly failing to build. I'm building on CLion.
As I'm kinda new to OpenCV I have some issues to narrow down the problem. I tried two different programs.
Number 1 is this one:
#include <iostream>
#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/imgproc/imgproc.hpp>
int main(int argc, char **argv) {
IplImage *img = cvLoadImage(argv[1]);
cvNamedWindow("Example1", CV_WINDOW_AUTOSIZE );
cvShowImage("Example1", img);
cvWaitKey(0);
cvReleaseImage(&img);
cvDestroyWindow("Example1" );
}
Which fails with:
Scanning dependencies of target untitled
[ 50%] Building CXX object CMakeFiles/untitled.dir/main.cpp.o
[100%] Linking CXX executable untitled
CMakeFiles/untitled.dir/main.cpp.o: In function `main':
/home/computervision/CLionProjects/untitled/main.cpp:7: undefined reference to `cvLoadImage'
/home/computervision/CLionProjects/untitled/main.cpp:8: undefined reference to `cvNamedWindow'
/home/computervision/CLionProjects/untitled/main.cpp:9: undefined reference to `cvShowImage'
/home/computervision/CLionProjects/untitled/main.cpp:10: undefined reference to `cvWaitKey'
/home/computervision/CLionProjects/untitled/main.cpp:11: undefined reference to `cvReleaseImage'
/home/computervision/CLionProjects/untitled/main.cpp:12: undefined reference to `cvDestroyWindow'
collect2: error: ld returned 1 exit status
CMakeFiles/untitled.dir/build.make:94: recipe for target 'untitled' failed
make[3]: *** [untitled] Error 1
CMakeFiles/Makefile2:67: recipe for target 'CMakeFiles/untitled.dir/all' failed
make[2]: *** [CMakeFiles/untitled.dir/all] Error 2
CMakeFiles/Makefile2:79: recipe for target 'CMakeFiles/untitled.dir/rule' failed
make[1]: *** [CMakeFiles/untitled.dir/rule] Error 2
Makefile:118: recipe for target 'untitled' failed
make: *** [untitled] Error 2
My 2nd one is this:
#include <iostream>
#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/imgproc/imgproc.hpp>
int main( int argc, char** argv ) {
cv::Mat image;
image = cv::imread("sample.jpeg" , CV_LOAD_IMAGE_COLOR);
if(! image.data ) {
std::cout << "Could not open or find the image" << std::endl ;
return -1;
}
cv::namedWindow( "Display window", cv::WINDOW_AUTOSIZE );
cv::imshow( "Display window", image );
cv::waitKey(0);
return 0;
}
Which fails with:
Scanning dependencies of target untitled
[ 50%] Building CXX object CMakeFiles/untitled.dir/main.cpp.o
[100%] Linking CXX executable untitled
CMakeFiles/untitled.dir/main.cpp.o: In function `main':
/home/computervision/CLionProjects/untitled/main.cpp:9: undefined reference to `cv::imread(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, int)'
/home/computervision/CLionProjects/untitled/main.cpp:16: undefined reference to `cv::namedWindow(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, int)'
/home/computervision/CLionProjects/untitled/main.cpp:17: undefined reference to `cv::_InputArray::_InputArray(cv::Mat const&)'
/home/computervision/CLionProjects/untitled/main.cpp:17: undefined reference to `cv::imshow(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, cv::_InputArray const&)'
/home/computervision/CLionProjects/untitled/main.cpp:19: undefined reference to `cv::waitKey(int)'
CMakeFiles/untitled.dir/main.cpp.o: In function `cv::Mat::~Mat()':
/usr/local/include/opencv2/core/mat.hpp:278: undefined reference to `cv::fastFree(void*)'
CMakeFiles/untitled.dir/main.cpp.o: In function `cv::Mat::operator=(cv::Mat const&)':
/usr/local/include/opencv2/core/mat.hpp:298: undefined reference to `cv::Mat::copySize(cv::Mat const&)'
CMakeFiles/untitled.dir/main.cpp.o: In function `cv::Mat::release()':
/usr/local/include/opencv2/core/mat.hpp:367: undefined reference to `cv::Mat::deallocate()'
collect2: error: ld returned 1 exit status
CMakeFiles/untitled.dir/build.make:94: recipe for target 'untitled' failed
make[3]: *** [untitled] Error 1
CMakeFiles/Makefile2:67: recipe for target 'CMakeFiles/untitled.dir/all' failed
make[2]: *** [CMakeFiles/untitled.dir/all] Error 2
CMakeFiles/Makefile2:79: recipe for target 'CMakeFiles/untitled.dir/rule' failed
make[1]: *** [CMakeFiles/untitled.dir/rule] Error 2
Makefile:118: recipe for target 'untitled' failed
make: *** [untitled] Error 2
My CMakeLists.txt:
cmake_minimum_required(VERSION 3.9)
project(untitled)
set(CMAKE_CXX_STANDARD 11)
add_executable(untitled main.cpp)
I wonder what I could have done so wrong.
Most searches lead to wrong settings of the g++ command, but I assume CLion knows what it's doing (also I tried with the command too, same errors).
For instance this here: openCV error : undefined reference to `cvLoadImage' Ubuntu
I assume highgui is not linked properly. Which might be the case, my output of:
computervision#computervision-VirtualBox:~/ex$ pkg-config opencv --libs
/usr/local/lib/libopencv_core.so /usr/local/lib/libopencv_flann.so /usr/local/lib/libopencv_ml.so
looks kinda poor, I assume I made a mistake during installation (just which?).
Another error might be the CMakeLists.txt. Here it was recommended to change it. But the line
LIBRARIES += glog gflags protobuf leveldb snappy
causes an error.
Executing
export CMAKE_CXX_FLAGS=`pkg-config opencv --cflags --libs`
before starting CLion doesn't make any difference either.
EDIT:
Using cmake:
computervision#computervision-VirtualBox:~/CLionProjects/untitled$ cmake .
-- The C compiler identification is GNU 5.4.0
-- The CXX compiler identification is GNU 5.4.0
-- Check for working C compiler: /usr/bin/cc
-- Check for working C compiler: /usr/bin/cc -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Detecting C compile features
-- Detecting C compile features - done
-- Check for working CXX compiler: /usr/bin/c++
-- Check for working CXX compiler: /usr/bin/c++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done
OpenCV_LIBS: opencv_mlopencv_flannopencv_core
-- Configuring done
-- Generating done
-- Build files have been written to: /home/computervision/CLionProjects/untitled
computervision#computervision-VirtualBox:~/CLionProjects/untitled$ g++ -o untitled main.cpp `pkg-config opencv --cflags --libs`
/tmp/ccdAr2hr.o: In function `main':
main.cpp:(.text+0x78): undefined reference to `cv::imread(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, int)'
main.cpp:(.text+0x128): undefined reference to `cv::namedWindow(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, int)'
main.cpp:(.text+0x1a2): undefined reference to `cv::imshow(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, cv::_InputArray const&)'
main.cpp:(.text+0x1ca): undefined reference to `cv::waitKey(int)'
collect2: error: ld returned 1 exit status
EDIT (2):
Using make after cmake:
computervision#computervision-VirtualBox:~/CLionProjects/untitled$ make
Scanning dependencies of target untitled
[ 50%] Building CXX object CMakeFiles/untitled.dir/main.cpp.o
[100%] Linking CXX executable untitled
CMakeFiles/untitled.dir/main.cpp.o: In function `main':
main.cpp:(.text+0x78): undefined reference to `cv::imread(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, int)'
main.cpp:(.text+0x128): undefined reference to `cv::namedWindow(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, int)'
main.cpp:(.text+0x1a2): undefined reference to `cv::imshow(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, cv::_InputArray const&)'
main.cpp:(.text+0x1ca): undefined reference to `cv::waitKey(int)'
collect2: error: ld returned 1 exit status
CMakeFiles/untitled.dir/build.make:97: recipe for target 'untitled' failed
make[2]: *** [untitled] Error 1
CMakeFiles/Makefile2:67: recipe for target 'CMakeFiles/untitled.dir/all' failed
make[1]: *** [CMakeFiles/untitled.dir/all] Error 2
Makefile:83: recipe for target 'all' failed
make: *** [all] Error 2

Answer 1

Linking OpenCV in CMakeLists.txt is missing.
cmake_minimum_required(VERSION 3.9)
project(untitled)
set(CMAKE_CXX_STANDARD 11)
find_package( OpenCV REQUIRED ) # locate OpenCV in system
include_directories( ${OpenCV_INCLUDE_DIRS} ) # provide library headers
add_executable(untitled main.cpp)
target_link_libraries( untitled ${OpenCV_LIBS} /usr/lib/x86_64-linux-gnu/libopencv_highgui.so) # link OpenCV libraries , hightgui.so not found by cmake so this hack
MESSAGE("OpenCV_LIBS: " ${OpenCV_LIBS} ) #display opencv libs found
if your compiler finds OpenCV and after executing cmake it should show OpenCV libraries found.