Using OpenCV with QT 6 and CMake

OzgurA

Hello dear Members,
I have installed opencv to my local windows computer and created a basic QT core application.
I use QT Creator 6.0.2 and OpenCV 4.5.5
I added find_package(OpenCV REQUIRED) to cmakelists.txt and some messages to trace value of opencv variables such as below.
message(STATUS " version: ${OpenCV_VERSION}")
message(STATUS " libraries: ${OpenCV_LIBS}")
message(STATUS " include path: ${OpenCV_INCLUDE_DIRS}")
message(STATUS " dir path: ${OpenCV_DIR}")
and these are the values

-- version: 4.5.5
-- libraries: opencv_calib3d;opencv_core;opencv_dnn;opencv_features2d;opencv_flann;opencv_gapi;opencv_highgui;opencv_imgcodecs;opencv_imgproc;opencv_ml;opencv_objdetect;opencv_photo;opencv_stitching;opencv_video;opencv_videoio;opencv_world
-- include path: C:/opencv/build/include
-- dir path: C:/OpenCV/build/x64/vc15/lib

As you can see the directory structure of opencv.
content of main.cpp is also below

#include <QCoreApplication>
#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/imgproc/imgproc.hpp>

int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);

cv::Mat mat;
return a.exec();

}

When I build the app, I got the error below

:-1: error: CMakeFiles/QT2.dir/main.cpp.obj:C:/Users/ozgurA/Documents/QT/QT2/main.cpp:10: undefined reference to `cv::Mat::Mat()'

I hope anyone can help me.

Best regards.

Christian Ehrlicher

Your application should link against the OpenCV libs -> target_link_libraries()

OzgurA

First of all thank you for your quick reply. As you can see below I have already linked libraries.

target_link_libraries(QT2 ${OpenCV_LIBS} Qt${QT_VERSION_MAJOR}::Core)

OpenCV_LIBS variable contains libraries below;

-- version: 4.5.5
-- libraries: opencv_calib3d;opencv_core;opencv_dnn;opencv_features2d;opencv_flann;opencv_gapi;opencv_highgui;opencv_imgcodecs;opencv_imgproc;opencv_ml;opencv_objdetect;opencv_photo;opencv_stitching;opencv_video;opencv_videoio;opencv_world

SGaist

Hi and welcome to devnet,

Did you try the example shown here ?

It's for Linux however the code and cmake file should work all the same on Windows.

OzgurA

Hi, my cmake configuration is almost same. You can check it below.

cmake_minimum_required(VERSION 3.14)
project(QT2 LANGUAGES CXX)
set(CMAKE_INCLUDE_CURRENT_DIR ON)
set(CMAKE_AUTOUIC ON)
set(CMAKE_AUTOMOC ON)
set(CMAKE_AUTORCC ON)
set(CMAKE_CXX_STANDARD 11)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

find_package(QT NAMES Qt6 Qt5 COMPONENTS Core REQUIRED)

find_package(Qt${QT_VERSION_MAJOR} COMPONENTS Core REQUIRED)
find_package(OpenCV REQUIRED)
include_directories( ${OpenCV_INCLUDE_DIRS} )
add_executable(QT2
main.cpp
)

target_link_libraries(QT2 ${OpenCV_LIBS} Qt${QT_VERSION_MAJOR}::Core)

I still get same error.

:-1: error: CMakeFiles/QT2.dir/main.cpp.obj:C:/Users/ozgurA/Documents/QT/QT2/main.cpp:11: undefined reference to `cv::Mat::Mat()'

SGaist

How did you install OpenCV ?

OzgurA

I have downloaded OpenCV 4.5.5 from the link https://opencv.org/releases/
then extracted into c:\opencv folder. After then set C:\OpenCV\build\x64\vc15\bin and C:\OpenCV\build\x64\vc15\lib folders into Path variable in Environment variables.

SGaist

Can you check with the previous version to see if the same is happening ?

OzgurA

If you mean previous version of OpenCV, yes I tried with 4.5.4 also but result is same.
Also I tried QT 6.2.1 and 6.2.2 but result is same.

SGaist

As suggested before, try building your application without Qt in it to ensure that your OpenCV installation is working.

jiapei100

Great question ...
It's now the issue of:
OpenCV-4.5.5 + Qt-6.3.0 + ffmpeg-5.0

A little headache...

oniongarlic

This worked for me for the Qt+OpenCV+Windows combo. Extracted the OpenCV windows binary release into C:\Qt\opencv

CMake for opencv includes and libraries

set(OpenCV_DIR "C:/Qt/opencv/build")

find_package(OpenCV REQUIRED)
include_directories( ${OpenCV_INCLUDE_DIRS} )

add_executable(qtopencv
  main.cpp
)
target_link_libraries(qtopencv Qt${QT_VERSION_MAJOR}::Core ${OpenCV_LIBS})

domidunas

This worked for me