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undefined reference to `cv::imshow(cv::String const&, cv::_InputArray const&)' with QT5.8

asked 2018-12-07 04:24:25 -0500

My pltform:

  • Win10 64bit
  • QT58(mingw53)

after installing opencv 3.30, I write code:

#include <iostream>
#include <QDir>
#include <qdebug>
#include "opencv2/opencv.hpp"
using namespace std;
int main()
    qDebug()<< QDir::currentPath();
    cv::Mat image = cv::imread("1.jpg",1);
    std::cout << image.cols << " " << image.rows << std::endl;
    if( == 0){
        cout << "No Image" <<endl;
        cout << "Image" << endl;
   cv::namedWindow("My Image");
   cv::imshow("My Image", image);

   return 0;

I get the error, like this:

release/main.o:main.cpp:(.text.startup+0x170): undefined reference to `cv::imshow(cv::String const&, cv::_InputArray const&)'
collect2.exe: error: ld returned 1 exit status

I dont know why, but other functions work well,expect imshow(). And I did add the LIBS:

INCLUDEPATH += D:\opencv\build\mingw\include

LIBS += D:\opencv\build\mingw\x86\mingw\bin\libopencv_highgui330.dll
LIBS += D:\opencv\build\mingw\x86\mingw\bin\libopencv_calib3d330.dll
LIBS += D:\opencv\build\mingw\x86\mingw\bin\libopencv_dnn330.dll
LIBS += D:\opencv\build\mingw\x86\mingw\bin\libopencv_features2d330.dll
LIBS += D:\opencv\build\mingw\x86\mingw\bin\libopencv_flann330.dll
LIBS += D:\opencv\build\mingw\x86\mingw\bin\libopencv_imgcodecs330.dll
LIBS += D:\opencv\build\mingw\x86\mingw\bin\libopencv_imgproc330.dll
LIBS += D:\opencv\build\mingw\x86\mingw\bin\libopencv_ml330.dll
LIBS += D:\opencv\build\mingw\x86\mingw\bin\libopencv_objdetect330.dll
LIBS += D:\opencv\build\mingw\x86\mingw\bin\libopencv_photo330.dll
LIBS += D:\opencv\build\mingw\x86\mingw\bin\libopencv_shape330.dll
LIBS += D:\opencv\build\mingw\x86\mingw\bin\libopencv_stitching330.dll
LIBS += D:\opencv\build\mingw\x86\mingw\bin\libopencv_superres330.dll
LIBS += D:\opencv\build\mingw\x86\mingw\bin\libopencv_video330.dll
LIBS += D:\opencv\build\mingw\x86\mingw\bin\libopencv_videoio330.dll
LIBS += D:\opencv\build\mingw\x86\mingw\bin\libopencv_videostab330.dll
LIBS += D:\opencv\build\mingw\x86\mingw\bin\opencv_ffmpeg330.dll
LIBS += D:\opencv\build\mingw\x86\mingw\bin\libopencv_core330.dll
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2 answers

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answered 2018-12-07 05:20:55 -0500

berak gravatar image

updated 2018-12-07 05:21:26 -0500

you have to link libs, not dlls

(*.dll.a in the case of mingw)

also, if you want to use mingw, step #1 would be: build opencv libs from src, using cmake.

other functions work well,

no, your linker just stops complaining after the 1st error.

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there is also no need for opencv_ffmpeg330.dll (it will be loaded dynamically, on demand, if nessecary)

berak gravatar imageberak ( 2018-12-07 05:35:09 -0500 )edit

I have built the src with Cmake. *.dll is dynamic link library,*.dll.a is static link library. QT is linked dynamically by default. Especially, imread() have successfully loaded the image, which means some functions do work.

GhostRider gravatar imageGhostRider ( 2018-12-07 08:30:01 -0500 )edit

qt != opencv

(and the dll.a libs are "stub" libs (containing the dlopen/dlsym calls), not static libs (which are plain .a))

berak gravatar imageberak ( 2018-12-07 08:35:18 -0500 )edit

So, I should add LIBS += *.dll.a? Also, what does “stub” libs mean?

GhostRider gravatar imageGhostRider ( 2018-12-07 08:40:24 -0500 )edit

yes, i think, you should use dll.a instead of dll.

and stub means -- those libs only resolve the function pointer from a dll, and pass it on to your program, the actual code is still in the dll.

berak gravatar imageberak ( 2018-12-07 09:11:10 -0500 )edit

uh...I just have try to use *dll.a, but system display "miss *.dll",when I run the test.exe. Instead , it is ok with *.dll

GhostRider gravatar imageGhostRider ( 2018-12-07 09:24:00 -0500 )edit

good ! so it all linked fine now !.

next step: put the folder containing the dll's on the PATH env var, so your exe can find them at runtime

(you might need to restart your cmdline / ide, so it can pick up the changes)

berak gravatar imageberak ( 2018-12-07 09:25:49 -0500 )edit

there is still a problem with imshow()

GhostRider gravatar imageGhostRider ( 2018-12-07 09:27:49 -0500 )edit

IF it built a test.exe, it must be a different problem, now, -- which is ?

berak gravatar imageberak ( 2018-12-07 09:30:48 -0500 )edit

Nope,,same as above.

GhostRider gravatar imageGhostRider ( 2018-12-07 09:32:21 -0500 )edit

answered 2018-12-13 02:53:38 -0500

The solution is to build opencv with debug mode. But I do not know why part of API are not linked in opencv library built with release mode.

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Asked: 2018-12-07 04:24:25 -0500

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Last updated: Dec 13 '18