Opencv + Qt first basic application not working

[sayze93]

So I installed openCV and wanted to make a very basic program with Qt, when I compiled and ran the program it would return a command line window with the message "press <return> to close" and the Qt output panel printed "...exe exited with code 0" ??

I know that it means there were no errors and everything was successful but why didnt it execute the actual code which is suppose to get the cameras video and display it in a new window.

Btw here is my code:

#include <QCoreApplication>
#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>
 
#include <QtCore>
 
int main(int argc, char *argv[])
{
 QCoreApplication a(argc, argv);
 
     cv::VideoCapture cam = cv::VideoCapture(0);
     cv::Mat frame;
     cv::namedWindow ("Demo", CV_WINDOW_AUTOSIZE);
 
     while (1) {
         cam >> frame;
         imshow ("Demo", frame);
     }
 
     cam.release();
     return 0;
 
 
 }

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

#include <QtCore>

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

     cv::VideoCapture cam = cv::VideoCapture(0);
     cv::Mat frame;
     cv::namedWindow ("Demo", CV_WINDOW_AUTOSIZE);

     while (1) {
         cam >> frame;
         imshow ("Demo", frame);
     }

     cam.release();
     return 0;


 }

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And here is my .pro file if it matters:

QT       += core
 
QT       -= gui
 
TARGET = WebCam
CONFIG   += console
CONFIG   -= app_bundle
 
TEMPLATE = app
 
 
SOURCES += main.cpp
 
INCLUDEPATH += "C:\openCV24\opencv_bin\install\include"
 
LIBS += "C:\openCV24\opencv\build\x86\mingw\lib\libopencv_calib3d240.dll.a"
LIBS += "C:\openCV24\opencv\build\x86\mingw\lib\libopencv_contrib240.dll.a"
LIBS += "C:\openCV24\opencv\build\x86\mingw\lib\libopencv_core240.dll.a"
LIBS += "C:\openCV24\opencv\build\x86\mingw\lib\libopencv_features2d240.dll.a"
LIBS += "C:\openCV24\opencv\build\x86\mingw\lib\libopencv_flann240.dll.a"
LIBS += "C:\openCV24\opencv\build\x86\mingw\lib\libopencv_gpu240.dll.a"
LIBS += "C:\openCV24\opencv\build\x86\mingw\lib\libopencv_highgui240.dll.a"
LIBS += "C:\openCV24\opencv\build\x86\mingw\lib\libopencv_imgproc240.dll.a"
LIBS += "C:\openCV24\opencv\build\x86\mingw\lib\libopencv_legacy240.dll.a"
LIBS += "C:\openCV24\opencv\build\x86\mingw\lib\libopencv_ml240.dll.a"
LIBS += "C:\openCV24\opencv\build\x86\mingw\lib\libopencv_nonfree240.dll.a"
LIBS += "C:\openCV24\opencv\build\x86\mingw\lib\libopencv_objdetect240.dll.a"
LIBS += "C:\openCV24\opencv\build\x86\mingw\lib\libopencv_photo240.dll.a"
LIBS += "C:\openCV24\opencv\build\x86\mingw\lib\libopencv_stitching240.dll.a"
LIBS += "C:\openCV24\opencv\build\x86\mingw\lib\libopencv_video240.dll.a"
LIBS += "C:\openCV24\opencv\build\x86\mingw\lib\libopencv_videostab240.dll.a"

QT       += core

QT       -= gui

TARGET = WebCam
CONFIG   += console
CONFIG   -= app_bundle

TEMPLATE = app


SOURCES += main.cpp

INCLUDEPATH += "C:\openCV24\opencv_bin\install\include"

LIBS += "C:\openCV24\opencv\build\x86\mingw\lib\libopencv_calib3d240.dll.a"
LIBS += "C:\openCV24\opencv\build\x86\mingw\lib\libopencv_contrib240.dll.a"
LIBS += "C:\openCV24\opencv\build\x86\mingw\lib\libopencv_core240.dll.a"
LIBS += "C:\openCV24\opencv\build\x86\mingw\lib\libopencv_features2d240.dll.a"
LIBS += "C:\openCV24\opencv\build\x86\mingw\lib\libopencv_flann240.dll.a"
LIBS += "C:\openCV24\opencv\build\x86\mingw\lib\libopencv_gpu240.dll.a"
LIBS += "C:\openCV24\opencv\build\x86\mingw\lib\libopencv_highgui240.dll.a"
LIBS += "C:\openCV24\opencv\build\x86\mingw\lib\libopencv_imgproc240.dll.a"
LIBS += "C:\openCV24\opencv\build\x86\mingw\lib\libopencv_legacy240.dll.a"
LIBS += "C:\openCV24\opencv\build\x86\mingw\lib\libopencv_ml240.dll.a"
LIBS += "C:\openCV24\opencv\build\x86\mingw\lib\libopencv_nonfree240.dll.a"
LIBS += "C:\openCV24\opencv\build\x86\mingw\lib\libopencv_objdetect240.dll.a"
LIBS += "C:\openCV24\opencv\build\x86\mingw\lib\libopencv_photo240.dll.a"
LIBS += "C:\openCV24\opencv\build\x86\mingw\lib\libopencv_stitching240.dll.a"
LIBS += "C:\openCV24\opencv\build\x86\mingw\lib\libopencv_video240.dll.a"
LIBS += "C:\openCV24\opencv\build\x86\mingw\lib\libopencv_videostab240.dll.a"

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Thanks appreciate any help to get me up and running

[ChrisW67]

If your program is terminating on its own then the program is never reaching line 15. If it reached this line it would never return. The only exit before this point is an abnormal termination.

Assuming your OpenCV has been compiled with Qt support (otherwise this question has nothing to do with Qt) the debug output probably contains a message like:

QWidget: Cannot create a QWidget when no GUI is being used
Aborted

QWidget: Cannot create a QWidget when no GUI is being used
Aborted

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You need to use QApplication and link the Qt gui library. Then you can worry about making the program do what you expect.