Why cant I compile this OpenCV 'hello world' using g++?

Question

I have installed OpenCV via homebrew, for my Mac OSX.

The problem I am having is that I am unable to use the imread openCV command at all. When I do, I get an error. Here is a breakdown of what I have done.

My simple code is:

#include <iostream>
#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>

using namespace std;
using namespace cv;

int main()
{

    Mat imageMe = imread("frog.jpg", 0);
    return 0;
}

To compile, I type this into the command prompt:

  g++ opencvEntry.cpp -o opencvEntry `pkg-config --cflags --libs opencv` && ./opencvEntry

Upon doing that, the error message I get is:

Undefined symbols for architecture x86_64:
      "cv::imread(std::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, int)", referenced from:
          _main in ccvT5f6R.o
    ld: symbol(s) not found for architecture x86_64
    collect2: error: ld returned 1 exit status

So... I am not sure where/what is going on here. If I simply uncomment the imread line the file compiles just fine. However when uncommented, it does not recognize the command.

What is going on here?

Answer 1

I have the same issue, after searching, this is a solution which works for me, hope it can help you as well.

Compiling OpenCV code on a 64-bit mac

need LDFLAG of "-lopencv_imgproc".