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cmd/cgo: undefined reference to OpenCV C++ function call #30800

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StefanCepa opened this issue Mar 13, 2019 · 4 comments
Closed

cmd/cgo: undefined reference to OpenCV C++ function call #30800

StefanCepa opened this issue Mar 13, 2019 · 4 comments
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FrozenDueToAge NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. WaitingForInfo Issue is not actionable because of missing required information, which needs to be provided.

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@StefanCepa
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StefanCepa commented Mar 13, 2019 •
edited

What version of Go are you using (go version)? 1.12

What operating system and processor architecture are you using (go env)?

GOARCH="amd64"
GOBIN=""
GOCACHE="/home/stefan/.cache/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/stefan/go"
GOPROXY=""
GORACE=""
GOROOT="/usr/local/go"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build128313540=/tmp/go-build -gno-record-gcc-switches"
go env Output
$ go env

What did you do?

I have successfully installed gocv package from https://github.com/hybridgroup/gocv and I am trying to run C++ code which I wrapped in C library inside my Go project. But there seems to be the problem when I try to call cv::optflow::createOptFlow_DualTVL1() method. I get undefined reference error. I dont know why, since in optflow.hpp file there is a method called createOptFlow_DualTVL1()

Here is my main.go:

package main


/*
#cgo LDFLAGS: -L/usr/local/lib -lopencv_core -lopencv_video -lopencv_videoio -lopencv_highgui -lopencv_tracking -lopencv_optflow
#include "dense_flow.h"
*/
import (
       "C"
       "gocv.io/x/gocv"
)

func main(){

}

Here is dense_flow.h:

#ifndef DENSEFLOW_DENSE_FLOW_H
#define DENSEFLOW_DENSE_FLOW_H


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

#include "opencv2/opencv.hpp"
#include "opencv2/optflow.hpp"
#include <iostream>
	
using namespace std;
using namespace cv;
using namespace cv::optflow;

EXTERNC void CalcOpticalFlowTVL1(Mat* , Mat*, Mat*);


#endif //DENSEFLOW_DENSE_FLOW_H

And here is dense_flow.cpp:

#include "dense_flow.h"

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


EXTERNC void CalcOpticalFlowTVL1(Mat* previousFrame, Mat* currentFrame, Mat* flow){
	Ptr<DualTVL1OpticalFlow> tvl1 = createOptFlow_DualTVL1();
	tvl1->calc(*previousFrame, *currentFrame, *flow);
}

What did you expect to see?

For my program to be built.

What did you see instead?

#_/home/stefan/Desktop/GoLang/OpticalFlow
/tmp/go-build442589631/b001/_x003.o: In function CalcOpticalFlowTVL1': ./dense_flow.cpp:12: undefined reference to cv::optflow::createOptFlow_DualTVL1()'
collect2: error: ld returned 1 exit status
@katiehockman katiehockman changed the title Undefined Reference to OpenCV C++ function call cgo: undefined reference to OpenCV C++ function call Mar 19, 2019
@katiehockman katiehockman changed the title cgo: undefined reference to OpenCV C++ function call go/src/runtime/cgo: undefined reference to OpenCV C++ function call Mar 19, 2019
@katiehockman
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/cc @ianlancetaylor
I don't know enough about cgo to guess what's going on here. Nothing is jumping out, any ideas?

@katiehockman katiehockman added the NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. label Mar 19, 2019
@ianlancetaylor
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When using a Unix linker the order of -l options matters. Without knowing anything about this code I would guess that you need to put -lopencv_core at the end of the list, not the beginning.

If that doesn't help, use nm -C to find which library defines the function cv::optflow::createOptFlow_DualTVL1().

@ianlancetaylor ianlancetaylor changed the title go/src/runtime/cgo: undefined reference to OpenCV C++ function call cmd/cgo: undefined reference to OpenCV C++ function call Mar 19, 2019
@ianlancetaylor ianlancetaylor added the WaitingForInfo Issue is not actionable because of missing required information, which needs to be provided. label Mar 19, 2019
@gopherbot
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Timed out in state WaitingForInfo. Closing.

(I am just a bot, though. Please speak up if this is a mistake or you have the requested information.)

@PoisonBOx
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have you ever solved the problem?

@golang golang locked and limited conversation to collaborators Apr 8, 2021
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@ianlancetaylor @PoisonBOx @gopherbot @katiehockman @StefanCepa