opencv error: undefined reference to `cv::VideoCapture::VideoCapture()'

_hunter

I try to use opencv3.2 with qt5.7,but I always get those erros:
/home/hunter/cameraTt/main.cpp:17: error: undefined reference to cv::VideoCapture::open(int)' /home/hunter/cameraTt/main.cpp:18: error: undefined reference to cv::VideoCapture::isOpened() const'
/home/hunter/cameraTt/main.cpp:20: error: undefined reference to cv::VideoCapture::get(int) const' /home/hunter/cameraTt/main.cpp:22: error: undefined reference to cv::VideoCapture::operator>>(cv::Mat&)'
/home/hunter/cameraTt/main.cpp:24: error: undefined reference to `cv::VideoWriter::VideoWriter()'
....
.pro

INCLUDEPATH += /usr/local/include/opencv2

LIBS += /usr/local/lib/libopencv_shape.so \

      /usr/local/lib/libopencv_videoio.so \

main.cpp

#include "mainwindow.h"
#include <QApplication>
//#include<cv.h>
#include<QTimer>
#include<QPixmap>
#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/imgproc/imgproc.hpp>
//using namespace cv;
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
MainWindow w;
w.show();

cv::VideoCapture m_cap;
m_cap.open(0);
assert(m_cap.isOpened());

int rate = m_cap.get(CV_CAP_PROP_FPS);
cv::Mat frame;
m_cap>>frame;

cv::VideoWriter videowriter;
videowriter.open("test.wmv",CV_FOURCC('W','M','V','2'),30,cv::Size(frame.cols,frame.rows));
assert(videowriter.isOpened());

char keycode;
while ((keycode = cvWaitKey(30))) {
    if (keycode == 27) {
        break;
    }
    if (!m_cap.grab()) {
        break;
    }
    m_cap>>frame;
    videowriter<<frame;
}
videowriter.release();

return a.exec();

}

aha_1980

HI @_hunter,

LIBS += /usr/local/lib/libopencv_shape.so
/usr/local/lib/libopencv_videoio.so

Please change the linker lines to this,

LIBS += -L/usr/local/lib -lopencv_shape -lopencv_videoio

and try again.

If it does not work, please prove the linker command line from the compile log.

Regards

_hunter

@aha_1980 said in opencv error: undefined reference to `cv::VideoCapture::VideoCapture()':

compile log

sorry,i do not know the location of compile log.I did what you sugget and here are the new errors:
:-1: error: main.o: undefined reference to symbol '_ZN2cv6String10deallocateEv'
/usr/local/lib/libopencv_core.so.3.2:-1: error: error adding symbols: DSO missing from command line
:-1: error: collect2: error: ld returned 1 exit status

_hunter

@aha_1980 thank you with your help,i solved this error

aha_1980

@_hunter

Glad it worked. So please close this topic as SOLVED. Thanks.

SuganyaSP

@_hunter I'm also getting the same error.. How you solved it. Can you please help me?

jsulm

@SuganyaSP Did you do what @aha_1980 suggested?

Ahmed_Mostafa

@SuganyaSP i am working on ubuntu18 with qt 4.5.2 opencv4
solved this problem with

INCLUDEPATH += /usr/local/include/opencv4

LIBS += $(shell pkg-config opencv --libs)

LIBS += -L/usr/local/lib -lopencv_core -lopencv_imgcodecs -lopencv_highgui -lopencv_shape -lopencv_videoio -lopencv_imgproc

then make a "rebuid"