I jusst installed Opencv 4.1.1 from source, with python 3 bindings. My Python installation seems to work correctly, because if I run:

import cv2

I get '4.1.1'

However, I also want to use some C++ code. I had a previous installation of 3.4.3 that I built from source, and unfortunately I had deleted the build folder before uninstalling it. So, when I run this C++ code, which just finds the version number Macros and prints them:

#include <opencv2/core.hpp>

using namespace cv;
using namespace std;
int main( int argc, char** argv )
    //print opencv version
    printf("opencv version: %d.%d.%d\n",CV_VERSION_MAJOR,CV_VERSION_MINOR,CV_VERSION_REVISION);

    return 0;

When i compile with this command :

g++ -o get_version get_version.cpp -I/usr/local/include/opencv4/opencv2 -Lusr/local/lib -lopencv_core

It returned 3.4.3.

So, I wanted to fix this, so I found the old header files, and deleted them all (they were located in /usr/local/include/opencv2). But now when I try to compile my code, it gives me the error:

get_version.cpp:1:10: fatal error: opencv2/core.hpp: No such file or directory
#include <opencv2/core.hpp>
compilation terminated.

But, if I navigate to /usr/local/include/opencv4/opencv2/, I can see the file, core.hpp, so I don't know why the compiler can't find it.

So, why are my headers not linking correctly? And how can I fix this. I thought the command -I/usr/local/include/opencv4/opencv2 would allow it to find it. I have also already run

sudo ldconfig

Although I'm not sure what that command exactly does. Also, for those that don't know, opencv 4 doesn't automatically include a pkg-config file, so that is not a solution to this problem.

  • Have you tried -I/usr/local/include/opencv4? You should not install and delete files on share header locations. Use your OS' package manager to install the opencv version you want. What OS are you on?
    – hanxue
    Aug 18 '19 at 5:48
  • Mods, I think this question is more appropriately asked in StackOverflow. Would you consider moving it over?
    – hanxue
    Aug 18 '19 at 5:48
  • @hanxue, Thanks. And I would have liked to use my package manager to delete the old header files, but I made a mistake, and I had deleted the user from my system who had done the 3.4.3 install, so I didn't have the old "build" files anymore, so I couldn't uninstall the "correct" way. I'm running Ubuntu 18.04, I'm the only person who uses this computer, but I try to use "users" to isolate larger projects I'm working on.
    – Matt Lyons
    Aug 19 '19 at 20:30

Fixed it, changed my "include" argument was wrong. When I compile with the command below:

g++ -o get_version get_version.cpp -I/usr/local/include/opencv4 -L/usr/local/lib -lopencv_core

It works. I had an extra "opencv2" at the end of the argument.

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