can not compile opencv programs in ubuntu

Question

I have wrote a simple program like this

#include <opencv2/opencv.hpp>

using namespace cv;

int main(int argc, const char* argv[])
{
    Mat input = imread(argv[1], 0); //Load as grayscale
    //~ FAST detector;
    //~ vector<KeyPoint> keypoints;
    //~ FAST(input, keypoints, 0.2);

    // Add results to image and save.
    //~ Mat output;
    //~ drawKeypoints(input, keypoints, output);
    namedWindow ("Image", CV_WINDOW_FREERATIO);
    imshow("Image", input);
    //~ imwrite(argv[2], output);

    return 0;
}

Then compile program like this:

g++ `pkg-config --libs opencv` main.cpp

And here is output of g++:

/tmp/ccK1Sbrw.o: In function `main':
main.cpp:(.text+0x66): undefined reference to `cv::imread(std::string const&, int)'
main.cpp:(.text+0xc2): undefined reference to `cv::namedWindow(std::string const&, int)'
main.cpp:(.text+0xf6): undefined reference to `cv::_InputArray::_InputArray(cv::Mat const&)'
main.cpp:(.text+0x139): undefined reference to `cv::imshow(std::string const&, cv::_InputArray const&)'
/tmp/ccK1Sbrw.o: In function `cv::Mat::~Mat()':
main.cpp:(.text._ZN2cv3MatD2Ev[_ZN2cv3MatD5Ev]+0x39): undefined reference to `cv::fastFree(void*)'
/tmp/ccK1Sbrw.o: In function `cv::Mat::release()':
main.cpp:(.text._ZN2cv3Mat7releaseEv[_ZN2cv3Mat7releaseEv]+0x47): undefined reference to `cv::Mat::deallocate()'
collect2: error: ld returned 1 exit status

I have the library installed, I can see *.so and *.hpp files in their folders, and ld find them, but what does it complain about? there is nothing in .so files?!

Also, I do not have nonfree modules installed (I uset apt-get to install opencv), how can I get them? I need SIFT which is inside that module. Do I have to compile opencv myself?

Peer Sommerlund · Accepted Answer · 2013-10-10 11:58:38Z

1

It appears to me that you forgot to specify a module in

`pkg-config --libs MODULENAMEGOESHERE`

answered Oct 10, 2013 at 11:58

Peer Sommerlund

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2 Comments

vfsoraki Over a year ago

sorry, it was a typo. but the answer was here stackoverflow.com/questions/7816607/…

vfsoraki Over a year ago

what about nonfree? I see some opencv examples use that, but how to get that?

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