Running OpenCV-4.0.0 C++ function

Question

I have created a C API which exposes the functionality of C++ code. Here is the code for opencv_test.h:

#ifdef __cplusplus
#define EXTERNC extern "C"
#else
#define EXTERNC
#endif

EXTERNC void OpenVideo(char *filename);

#undef EXTERNC

Code for opencv_test.cpp:

#include <iostream>
#include <unistd.h>
#include "opencv_test.h"
#include "opencv2/opencv.hpp"

using namespace std;
using namespace cv;


void OpenVideo(char *filename){
    VideoCapture cap(filename);
    Mat Uframe;
    int frameCount = 0;

    if(!cap.isOpened()){
        cout<<"Cannot open video file!";
        return;
    }

    namedWindow("Video");
    while(++frameCount){

        bool success = cap.read(Uframe);

        if(!success){
            cout<<frameCount<<" frames read";
            break;      
        }

        imshow("Video", Uframe);
        waitKey(1);

    }

}

And finally, for opencvTest.go:

package main

/*
#cgo LDFLAGS: -L/usr/local/lib -lopencv_core -lopencv_video -lopencv_videoio -lopencv_highgui
#include <stdlib.h>
#include "opencv_test.h"
*/
import "C"

func main(){

    theFilename := "DRŽAVNI POSAO [HQ] - Ep.323 Dan žena (07.03.2014.).avi"
    C.OpenVideo(C.CString(theFilename))
}

And the error I am getting is the following:

---

command-line-arguments /tmp/go-build823465636/b001/_x002.o: In function "_cgo_dcf5d601f507_Cfunc_OpenVideo": /tmp/go-build/cgo-gcc-prolog:48: undefined reference to `OpenVideo' collect2: error: ld returned 1 exit status

---

Now I am not sure if I have to run any kind of special commands or something, I have read that just by importing "C" pseudo-package, my .go file will be build with cgo. So, if I have included my custom-made .h file, and the project is built using cgo, how come I get undefined reference to a function error?

EDIT:

Here is the whole output when running go build -x opencvTest.go command:

WORK=/tmp/go-build568047770

mkdir -p $WORK/b001/

cd /home/stefan/Desktop/GoLang

CGO_LDFLAGS='"-L/usr/local/lib" "-lopencv_core" "-lopencv_video" "-lopencv_videoio" "-lopencv_highgui" "-L/usr/local/lib" "-lopencv_core" "-lopencv_video" "-lopencv_videoio" "-lopencv_highgui"' /usr/local/go/pkg/tool/linux_amd64/cgo -objdir $WORK/b001/ -importpath command-line-arguments -- -I/usr/local/include -I $WORK/b001/ -g -O2 ./opencvTest.go

cd $WORK

gcc -fno-caret-diagnostics -c -x c - || true

gcc -Qunused-arguments -c -x c - || true

gcc -fdebug-prefix-map=a=b -c -x c - || true

gcc -gno-record-gcc-switches -c -x c - || true

cd $WORK/b001

TERM='dumb' gcc -I /home/stefan/Desktop/GoLang -fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=$WORK/b001=/tmp/go-build -gno-record-gcc-switches

-I/usr/local/include -I ./ -g -O2 -o ./_x001.o -c _cgo_export.c TERM='dumb' gcc -I /home/stefan/Desktop/GoLang -fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=$WORK/b001=/tmp/go-build -gno-record-gcc-switches

-I/usr/local/include -I ./ -g -O2 -o ./_x002.o -c opencvTest.cgo2.c TERM='dumb' gcc -I /home/stefan/Desktop/GoLang -fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=$WORK/b001=/tmp/go-build -gno-record-gcc-switches

-I/usr/local/include -I ./ -g -O2 -o ./_cgo_main.o -c _cgo_main.c cd /home/stefan/Desktop/GoLang TERM='dumb' gcc -I . -fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=$WORK/b001=/tmp/go-build -gno-record-gcc-switches -o $WORK/b001/cgo.o $WORK/b001/_cgo_main.o $WORK/b001/_x001.o $WORK/b001/_x002.o -L/usr/local/lib -lopencv_core -lopencv_video -lopencv_videoio -lopencv_highgui -L/usr/local/lib -lopencv_core -lopencv_video -lopencv_videoio -lopencv_highgui

command-line-arguments /tmp/go-build568047770/b001/_x002.o: In function _cgo_dcf5d601f507_Cfunc_OpenVideo': /tmp/go-build/cgo-gcc-prolog:48: undefined reference toOpenVideo' collect2: error: ld returned 1 exit status