undefined reference to `cv::VideoCapture::VideoCapture(int)

Question

i'm trying to use my webcam using C++ and OpenCV, but i'm gettin this error

(...):Images.cpp:(.text+0x27): undefined reference to cv::VideoCapture::VideoCapture(int)

(...):Images.cpp:(.text+0x38): undefined reference to cv::VideoCapture::~VideoCapture()

(...):Images.cpp:(.text$_ZN2cv6StringD1Ev[_ZN2cv6StringD1Ev]+0x11): undefined reference to cv::String::deallocate() ...

My code:

#include <iostream>
#include <string.h>
#include "opencv2/core/core.hpp"
#include "opencv2/opencv.hpp"
#include "opencv2/videoio/videoio.hpp"
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/video.hpp"
#include "opencv2/imgproc/imgproc.hpp"

using namespace std;
using namespace cv;


int main(int argc, char const *argv[])
{
    VideoCapture cap(0);
    return 0;
}

Which libraries have you linked? You are most probably missing some. — Lakshya Kejriwal, Sep 04 '17 at 23:52
@shawshank sorry, but i dont know about it :c i'm new to c++ — Felipe Machado, Sep 04 '17 at 23:59
Possible duplicate of [What is an undefined reference/unresolved external symbol error and how do I fix it?](https://stackoverflow.com/questions/12573816/what-is-an-undefined-reference-unresolved-external-symbol-error-and-how-do-i-fix) — user0042, Sep 05 '17 at 00:28

score 14 · Answer 1 · edited Oct 10 '18 at 16:44

14

I faced the same issue with respect to opencv version 3.4.3.

With reference to this example, I figured out that I was not including the libopencv_videoio. Once I added it to the project, the build was successful.

In opencv version 3, I think we also need to include the library -lopencv_videoio to use VideoCapture.

edited Oct 10 '18 at 16:44

Adil B

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answered Oct 10 '18 at 16:17

vishwanath_hugar

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A wierd thing. "g++ -Wall -o test2 `pkg-config --libs opencv` test2.cpp" did not work after checking opencv.pc had opencv_videoio in it, which it did. However "g++ -Wall -o test2 test.cpp `pkg-config --libs opencv`" did work. – Gavin Simpson Feb 12 '20 at 08:49

score 4 · Answer 2 · answered Sep 05 '17 at 00:06

4

The reason your code is not compiling is you are not giving the path of the libraries and the header files. Try compiling the code using the following command.

g++ main.cpp -o main -I <path to opencv header files> -L <path to opencv libraries> -l<name of libraries>

A sample example if you are using linux is

g++ main.cpp -o main -I /usr/local/include -L /usr/local/lib -lopencv_core -lopencv_highgui

Here I am assuming your header file are in /usr/local/include and libraries are in /usr/local/lib and lopencv_core is the name of your library

answered Sep 05 '17 at 00:06

Lakshya Kejriwal

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But i compile codes with others opencv's files. Only this file the code not work. Anyway i'll try – Felipe Machado Sep 05 '17 at 00:09
Yeah, same error. If i delete `VideoCapture cap(0);` the code compiles. – Felipe Machado Sep 05 '17 at 00:23
What all libraries have you included while compiling your code? – Lakshya Kejriwal Sep 05 '17 at 01:08

score 2 · Answer 3 · edited Mar 30 '19 at 14:27

2

I had the same problem after forking a Github project. I resolved it using these posts.
My problem was in the Makefile I forked, I had to replace these lines. oldLine:

$(EXECUTABLE): $(OBJECTS)
        $(CC) $(LDFLAGS) $(OBJECTS) -o $@

newLine:

$(EXECUTABLE): $(OBJECTS)
        $(CC) $(OBJECTS) $(LDFLAGS) -o $@

I hope it can help someone ;)

edited Mar 30 '19 at 14:27

Til

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answered Mar 30 '19 at 14:07

florian

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Dear sir thank you so much, your answer just saved my day. – Meto Oct 01 '20 at 08:29

score 1 · Answer 4 · answered Sep 19 '19 at 04:48

you probably missing opencv libs , try to add them to your project config file like

LIBS += -LC:\\opencv\\opeencv4.1\\x86\\mingw\\bin \
    libopencv_core410 \
    libopencv_highgui410 \
    libopencv_imgcodecs410 \
    libopencv_imgproc410 \
    libopencv_features2d410 \
    libopencv_video410 \
    libopencv_videoio410 \

undefined reference to `cv::VideoCapture::VideoCapture(int)

4 Answers4