OpenCv undefined reference to `cv::

Question

I am new at OpenCv. I am using Eclipse C/C++. When i try to run this sample code i faced with these errors. What should i do to solve this problem? Is there any problem at configurating ?

#using namespace std;
#using namespace cv;

    int main( int argc, const char** argv )
    {
         Mat img = imread("MyPic.JPG", CV_LOAD_IMAGE_UNCHANGED); 
         if (img.empty()) //check whether the image is loaded or not
         {
              cout << "Error : Image cannot be loaded..!!" << endl;
              //system("pause"); //wait for a key press
              return -1;
         }
         namedWindow("MyWindow", CV_WINDOW_AUTOSIZE); //create a window with the name "MyWindow"
         imshow("MyWindow", img); /
         waitKey(0); //wait infinite time for a keypress
         destroyWindow("MyWindow"); //destroy the window with the name, "MyWindow"

         return 0;
    }


16:11:28 **** Incremental Build of configuration Debug for project OpenCv ****
Info: Internal Builder is used for build
g++ "-IC:\\opencv\\build\\include" -O0 -g3 -Wall -c -fmessage-length=0 -o "src\\OpenCv.o" "..\\src\\OpenCv.cpp" 
g++ "-LC:\\opencv\\build\\x86\\vc12\\lib" -o OpenCv.exe "src\\OpenCv.o" -lopencv_calib3d249 -lopencv_contrib249 -lopencv_core249 -lopencv_features2d249 -lopencv_flann249 -lopencv_gpu249 -lopencv_highgui249 -lopencv_imgproc249 -lopencv_legacy249 -lopencv_ml249 -lopencv_nonfree249 -lopencv_objdetect249 -lopencv_ocl249 -lopencv_photo249 -lopencv_stitching249 -lopencv_superres249 -lopencv_ts249 -lopencv_video249 -lopencv_videostab249 
src\OpenCv.o: In function `main':
C:\Users\ayberk101\workspace\OpenCv\Debug/../src/OpenCv.cpp:10: undefined reference to `cv::imread(std::string const&, int)'
C:\Users\ayberk101\workspace\OpenCv\Debug/../src/OpenCv.cpp:19: undefined reference to `cv::namedWindow(std::string const&, int)'
C:\Users\ayberk101\workspace\OpenCv\Debug/../src/OpenCv.cpp:20: undefined reference to `cv::_InputArray::_InputArray(cv::Mat const&)'
C:\Users\ayberk101\workspace\OpenCv\Debug/../src/OpenCv.cpp:20: undefined reference to `cv::imshow(std::string const&, cv::_InputArray const&)'
C:\Users\ayberk101\workspace\OpenCv\Debug/../src/OpenCv.cpp:22: undefined reference to `cv::waitKey(int)'
C:\Users\ayberk101\workspace\OpenCv\Debug/../src/OpenCv.cpp:24: undefined reference to `cv::destroyWindow(std::string const&)'
src\OpenCv.o: In function `ZN2cv3MatD1Ev':
C:/opencv/build/include/opencv2/core/mat.hpp:278: undefined reference to `cv::fastFree(void*)'
src\OpenCv.o: In function `ZN2cv3Mat7releaseEv':
C:/opencv/build/include/opencv2/core/mat.hpp:367: undefined reference to `cv::Mat::deallocate()'
collect2.exe: error: ld returned 1 exit status

Solution

problem1: you will have to include opencv / c++ header files to make it work:

#include "opencv2/core/core.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include "opencv2/highgui/highgui.hpp"
#using namespace cv;

#include <iostream>
#using namespace std;

int main() {
...

---

then, problem2: you cannot use the vc12 libs with mingw. (it's a different compiler)

there are no more prebuild mingw libs for opencv, so, before doing anything else, you will have to build the opencv libs locally using cmake.

---

again, do you really need to use mingw / eclipse ? (vs express is still free)