Qt 5.6.1 with Opencv

[navya.dubey]

I have to use the opencv library in my project build in qt 5.6.1 with mingw compiler but I guess because I am unable to configure qt with opencv 3.9.0 this is the reason of several errors.
Please tell me the procedure to use qt with opencv.

[joeQ]

@navya.dubey Hi, friend.

1. you should to use LIBS in pro file to add the OpenCV libs path. like below snippet code:

INCALUDEPATH += opencv_headers_directory

# add opencv libs directory
LIBS += -Lopencv_libs_directory

# add libs such as core, highgui, imgcodecs...
LIBS += -lopencv_libs_name
LIBS += -lopencv_libs_name
LIBS += -lopencv_libs_name
LIBS += -lopencv_libs_name

2. In your source files

#include <opencv2/core.hpp>
#include <opecv2/highgui.hpp>
...

You can click reference link to get more informations about how to use third party libraried in Qt

Reference

Qt Third Party libraried Help

[navya.dubey]

hi @joeQ
I tried this but this error appears
I haven't set any privacy, I don't know the reason behind this error.

[joeQ]

@navya.dubey

Note: -L and -l

LIBS += -Lopencv_libs_directory

# add libs such as core, highgui, imgcodecs...
LIBS += -lopencv_libs_name
LIBS += -lopencv_libs_name

like

INCLUDE += C:/opencv/build/include

LIBS += -LC:/opencv/build/x86/vc14/lin

CONFIG(debug, debug|release) {
    # use debug lib
    LIBS += -lopencv_core2413d.lib
    LIBS += -lopencv_highgui2413d.lib
    LIBS += -lopencv_imgcodecs2413d.lib
    LIBS += -lopencv_imgproc2413d.lib
}

CONFIG(release, debug|release) {
    # use release lib
    LIBS += -lopencv_core2413.lib
    LIBS += -lopencv_highgui2413.lib
    LIBS += -lopencv_imgcodecs2413.lib
    LIBS += -lopencv_imgproc2413.lib
}

[navya.dubey]

@joeQ
I am so sorry but I didn't get the meaning of -L and -l . I have just included the whole path and it says" not found"

[joeQ]

@navya.dubey
use / try again, not use \ in the path string.

[navya.dubey]

@joeQ the problem still remains the same now the .pro file is not showing error but .cpp shows

[joeQ]

@navya.dubey

Hi guys, Can you be careful? Please to read you pro file code. why did you use debug lib twice?

I said not to use \ in any path. Please check you code carefully.

[navya.dubey]

@joeQ
I tried with / as well as with \ and the problem is same anyhow.
I deleted the repetition, problem still remains.

[joeQ]

@navya.dubey

did you include opencv head files?

[SGaist]

Hi,

In addition to all the good clues @joeQ provided, the main problem here is: trying to build an application with MinGW and link to a C++ library built with Visual Studio. It's not possible. You have to use a MinGW build of OpenCV to link to your application. Or use a VS build of Qt to link to your OpenCV lib built with Visual Studio. Note that prior to Visual Studio 2017, you also have to exactly match the versions of Visual Studio used to build everything C++ you might use in your project.

VS2017 has backward compatibility but only with VS2015.

[navya.dubey]

@SGaist hey I tried to build opencv using cmake following this tutorial
https://www.youtube.com/watch?v=ZOSu-2Oju-A
there are several errors while building the code
I followed all the steps in the video but the output is not same as of the video tutorial, I hope you understood the basic problem please help.

[SGaist]

You have to tell CMake where to find Qt in order for it to build its libhighgui with the Qt backend.

[navya.dubey]

@SGaist how to tell cmake where to find qt because I have set the environment variables of the system to know the location of mingw compiler in qt.
what to do next?

[mrjj]

@navya.dubey
Hi

like
cmake .. -DCMAKE_PREFIX_PATH="C:\Qt\5.7\msvc2015\lib\cmake\Qt5"

[navya.dubey]

Where to add it

[mrjj]

@navya.dubey
Sorry, i miss scrolled and edited your post.

You use it as commandline option when you call cmake as shown

[navya.dubey]

@mrjj You mean I have to go to the location where CMake is present and then I have to execute this command, right?

[mrjj]

@navya.dubey

No, you make sure there is path to cmake
then you go to the project folder where the Cmake.tx file is and then
call cmake

if no paths, you can fully tell

c:\programfile\whatever\cmake .. OPTION

Same way as done here
https://forum.qt.io/topic/82074/creating-a-multi-purpose-node-editor-if-there-is-none-available/20
its also a Cmake project

[SGaist]

You can also add that using the GUI you showed in your post.