Errors: undefined reference to cv::VideoCapture::VideoCapture()

[JonB]

@Pl45m4
Except that OP shows that certain items are missing from the link... :)

And now I see the OP's latest post shows linking with different libraries from the original post, so I hand the OP over to you... :)

[Pl45m4]

@JonB said in Errors: undefined reference to cv::VideoCapture::VideoCapture():

Except that OP shows that certain items are missing from the link... :)

Yeah, but linking opencv_worldXXX is not the issue here ;-)

So @Ronel_qtmaster wasn't wrong with his comment.

As:

@Arev said in Errors: undefined reference to cv::VideoCapture::VideoCapture():

I compile it with mingw32

and:

-L$$PWD/opencv/build/x64/vc16/lib/ -lopencv_world490

MinGW x32 vs. VC x64

That's not going to work ;-)

Edit:

@Arev said in Errors: undefined reference to cv::VideoCapture::VideoCapture():

I modified it and downloaded the opencv build for mingw from this repository

/x64/mingw/lib/

Then you still have to use MinGWx64

Btw:
Please don't post code as picture. Post as text using the code tags (</> button)

[Ronel_qtmaster]

@Arev First of all, you cannot download libraries of opencv 4.5.5 and use it with QT5.9.9 because there are uncompatible due to the mingw version of Qt5.9.

Moreover, are you sure that these built opencv librairies where to use with Qt5.9?

Again, you should instead download the sources of opencv, install cmake and build opencv.During the build you can insert your the qt version used for that opencv.

PS: cmake is only for building the sources of opencv in other to make them usable with your Qt version, Not to build your project

[Arev]

@Pl45m4
Oh, I download opencv build for x86 and errors fixed
But now my program doesn't open, I think the problem is in this line

static cv::VideoCapture cap;

[jsulm]

@Arev said in Errors: undefined reference to cv::VideoCapture::VideoCapture():

But now my program doesn't open

Then use debugger...

[Arev]

@jsulm

I try it and I get the error:
Executable failed: During startup program exited with code 0xc0000135.

[jsulm]

@Arev said in Errors: undefined reference to cv::VideoCapture::VideoCapture():

static cv::VideoCapture cap

Does it work without this line?
Why is cap static?

[Arev]

@jsulm

cv::VideoCapture:

This is a class from the OpenCV library used for capturing video from camera devices or video files. It provides methods to open, read, and manage video streams.
By declaring cap as static, it's accessible across all instances of the class, and there will be only one instance of it throughout the program execution.

[jsulm]

@Arev I did not ask what it is, I asked whether your app starts if this line is not there.

[Arev]

@jsulm

Oh sorry, I created another test app and added that line that nothing in the app depended on and it didn't work and didn't cause any problems, but without that line the app works.

[jsulm]

@Arev said in Errors: undefined reference to cv::VideoCapture::VideoCapture():

0xc0000135

This error code means: STATUS_DLL_NOT_FOUND
Looks like the cv libs are not found when starting your app. How do you start it? From QtCreator?

[Arev]

@jsulm

I can share code
This is my .pro

QT += quick

CONFIG += c++11
QT_DISABLE_DEPRECATED_BEFORE=0x060000  

SOURCES += \
        main.cpp \
        opencvimageprovider.cpp \
        videostreamer.cpp

RESOURCES += qml.qrc

QML_IMPORT_PATH =

QML_DESIGNER_IMPORT_PATH =

qnx: target.path = /tmp/$${TARGET}/bin
else: unix:!android: target.path = /opt/$${TARGET}/bin
!isEmpty(target.path): INSTALLS += target

HEADERS += \
    opencvimageprovider.h \
    videostreamer.h \

win32: LIBS += -L$$PWD/OpenCV-MinGW-Build-OpenCV-4.5.0-with-contrib/x64/mingw/lib/ -llibopencv_videoio450.dll
win32: LIBS += -L$$PWD/OpenCV-MinGW-Build-OpenCV-4.5.0-with-contrib/x64/mingw/lib/-llibopencv_calib3d450.dll
win32: LIBS += -L$$PWD/OpenCV-MinGW-Build-OpenCV-4.5.0-with-contrib/x64/mingw/lib/-llibopencv_core450.dll
win32: LIBS += -L$$PWD/OpenCV-MinGW-Build-OpenCV-4.5.0-with-contrib/x64/mingw/lib/-llibopencv_dnn450.dll
win32: LIBS += -L$$PWD/OpenCV-MinGW-Build-OpenCV-4.5.0-with-contrib/x64/mingw/lib/-llibopencv_features2d450.dll
win32: LIBS += -L$$PWD/OpenCV-MinGW-Build-OpenCV-4.5.0-with-contrib/x64/mingw/lib/-llibopencv_flann450.dll
win32: LIBS += -L$$PWD/OpenCV-MinGW-Build-OpenCV-4.5.0-with-contrib/x64/mingw/lib/-llibopencv_gapi450.dll
win32: LIBS += -L$$PWD/OpenCV-MinGW-Build-OpenCV-4.5.0-with-contrib/x64/mingw/lib/-llibopencv_highgui450.dll
win32: LIBS += -L$$PWD/OpenCV-MinGW-Build-OpenCV-4.5.0-with-contrib/x64/mingw/lib/-llibopencv_imgcodecs450.dll
win32: LIBS += -L$$PWD/OpenCV-MinGW-Build-OpenCV-4.5.0-with-contrib/x64/mingw/lib/-llibopencv_imgproc450.dll
win32: LIBS += -L$$PWD/OpenCV-MinGW-Build-OpenCV-4.5.0-with-contrib/x64/mingw/lib/-llibopencv_ml450.dll
win32: LIBS += -L$$PWD/OpenCV-MinGW-Build-OpenCV-4.5.0-with-contrib/x64/mingw/lib/-llibopencv_objdetect450.dll
win32: LIBS += -L$$PWD/OpenCV-MinGW-Build-OpenCV-4.5.0-with-contrib/x64/mingw/lib/-llibopencv_stitching450.dll
win32: LIBS += -L$$PWD/OpenCV-MinGW-Build-OpenCV-4.5.0-with-contrib/x64/mingw/lib/-llibopencv_photo450.dll
win32: LIBS += -L$$PWD/OpenCV-MinGW-Build-OpenCV-4.5.0-with-contrib/x64/mingw/lib/-llibopencv_video450.dll
win32: LIBS += -L$$PWD/OpenCV-MinGW-Build-OpenCV-4.5.0-with-contrib/x64/mingw/lib/-llibopencv_videoio450.dll

INCLUDEPATH += $$PWD/OpenCV-MinGW-Build-OpenCV-4.5.0-with-contrib/include
DEPENDPATH += $$PWD/OpenCV-MinGW-Build-OpenCV-4.5.0-with-contrib/include

win32: LIBS += -L$$PWD/OpenCV-MinGW-Build-OpenCV-4.5.0-with-contrib/x64/mingw/lib/ -llibopencv_core450.dll

INCLUDEPATH += $$PWD/OpenCV-MinGW-Build-OpenCV-4.5.0-with-contrib/include
DEPENDPATH += $$PWD/OpenCV-MinGW-Build-OpenCV-4.5.0-with-contrib/include

Main.cpp

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include "opencvimageprovider.h"
#include "videostreamer.h"
#include <QQmlContext>

int main(int argc, char *argv[])
{
    QGuiApplication app(argc, argv);

    QQmlApplicationEngine engine;

    qRegisterMetaType<cv::Mat>("cv::Mat");

    VideoStreamer videoStreamer;

    OpencvImageProvider *liveImageProvider(new OpencvImageProvider);

    engine.rootContext()->setContextProperty("VideoStreamer",&videoStreamer);
    engine.rootContext()->setContextProperty("liveImageProvider",liveImageProvider);

    engine.addImageProvider("live",liveImageProvider);

    const QUrl url(QStringLiteral("qrc:/main.qml"));

    engine.load(url);

    QObject::connect(&videoStreamer,&VideoStreamer::newImage,liveImageProvider,&OpencvImageProvider::updateImage);

    return app.exec();
}

VideoStreamer.h

#ifndef VIDEOSTREAMER_H
#define VIDEOSTREAMER_H

#include <QObject>
#include <QTimer>
#include <OpenCV-MinGW-Build-OpenCV-4.5.0-with-contrib/include/opencv2/opencv.hpp>
#include <QImage>
#include <iostream>
#include <QThread>


static cv::VideoCapture cap;


class VideoStreamer: public QObject
{
    Q_OBJECT
public:
    VideoStreamer();
    ~VideoStreamer();

public:
    void streamVideo();
    QThread* threadStreamer = new QThread();
    void catchFrame(cv::Mat emittedFrame);

public slots:
    void openVideoCamera(QString path);

    void streamerThreadSlot();

private:

    cv::Mat frame;
    QTimer tUpdate;

signals:
    void newImage(QImage &);

    void emitThreadImage(cv::Mat frameThread);
};

#endif // VIDEOSTREAMER_H

VideoStreamer.cpp

#include "videostreamer.h"

VideoStreamer::VideoStreamer()
{
    connect(&tUpdate,&QTimer::timeout,this,&VideoStreamer::streamVideo);

}

VideoStreamer::~VideoStreamer()
{
    cap.release();
    tUpdate.stop();
    threadStreamer->requestInterruption();
}

void VideoStreamer::streamVideo()
{

    if(frame.data)
    {
        QImage img = QImage(frame.data,frame.cols,frame.rows,QImage::Format_RGB888).rgbSwapped();
        emit newImage(img);
    }
}

void VideoStreamer::catchFrame(cv::Mat emittedFrame)
{
    frame = emittedFrame;
}

void VideoStreamer::openVideoCamera(QString path)
{
    if(path.length() == 1)
    cap.open(path.toInt());
    else
    cap.open(path.toStdString());

    VideoStreamer* worker = new VideoStreamer();
    worker->moveToThread(threadStreamer);
    QObject::connect(threadStreamer,SIGNAL(started()),worker,SLOT(streamerThreadSlot()));
    QObject::connect(worker,&VideoStreamer::emitThreadImage,this,&VideoStreamer::catchFrame);
    threadStreamer->start();

    double fps = cap.get(cv::CAP_PROP_FPS);
    tUpdate.start(1000/fps);
}

void VideoStreamer::streamerThreadSlot()
{
    cv::Mat tempFrame;

    while (1) {
        cap>>tempFrame;
        if(tempFrame.data)
            emit emitThreadImage(tempFrame);

        if(QThread::currentThread()->isInterruptionRequested())
        {
            cap.release();
            return;
        }

    }
}

OpencvImageProvider.h

#ifndef OPENCVIMAGEPROVIDER_H
#define OPENCVIMAGEPROVIDER_H


#include <QObject>
#include <QImage>
#include <QQuickImageProvider>

class OpencvImageProvider : public QObject, public QQuickImageProvider
{
    Q_OBJECT
public:
    OpencvImageProvider(QObject *parent = nullptr);

    QImage requestImage(const QString &id, QSize *size, const QSize &requestedSize) override;

public slots:
    void updateImage(const QImage &image);

signals:
    void imageChanged();

private:
    QImage image;
};

#endif // OPENCVIMAGEPROVIDER_H

OpencvImageProvider.cpp

#include "opencvimageprovider.h"

OpencvImageProvider::OpencvImageProvider(QObject *parent) : QObject(parent), QQuickImageProvider(QQuickImageProvider::Image)
{
    image = QImage(200,200,QImage::Format_RGB32);
    image.fill(QColor("black"));
}

QImage OpencvImageProvider::requestImage(const QString &id, QSize *size, const QSize &requestedSize)
{
    Q_UNUSED(id);

    if(size){
        *size = image.size();
    }

    if(requestedSize.width() > 0 && requestedSize.height() > 0) {
        image = image.scaled(requestedSize.width(), requestedSize.height(), Qt::KeepAspectRatio);
    }
    return image;
}

void OpencvImageProvider::updateImage(const QImage &image)
{
    if(!image.isNull() && this->image != image) {
        this->image = image;
        emit imageChanged();
    }
}

[jsulm]

@Arev You did not answer my question

[Arev]

@jsulm
Yes, from Qt creator

[Arev]

@jsulm

In the .pro file I have not added these two lines

CONFIG += link_pkgconfig
PKGCONFIG += opencv4

could this be the reason?
And after adding I get this problem:

opencv4 development package not found

[SGaist]

@Arev hi,

Are you sure about the pkgconfig package name ? If so, where is its .pc file located ?

[Arev]

@SGaist said in Errors: undefined reference to cv::VideoCapture::VideoCapture():

.pc

what is .pc file (
I do not have that file, where can I get

[SGaist]

@Arev it's the pkgconfig configuration file. Each library / framework can provide it (or you can create your own).