Why after linking the OpenCV libraries, Mat objects are still 'undefined'?

[georgiav]

@mrjj I tried to change it the way you suggested and using -l instead of -L but I still get those errors.

[mrjj]

@georgiav
Hi
make sure you do a build -> clean
and then run qmake
then recompile
or even better delete the build folder. qmake caches stuff so often a clean is needed.

[SGaist]

Your paths are invalid, use forward slashes for them.

[georgiav]

@SGaist @mrjj I changed the paths to this

INCLUDEPATH += -I/usr/include

LIBS += -l/usr/local/lib/libopencv_core.so
LIBS+= -l/usr/local/lib/libopencv_highgui.so
LIBS+= -l/usr/local/lib/libopencv_imgproc.so
Should it work now?
and did the cleaning process and now I have more errors but all because the libraries still seem to be unrecognised.

[SGaist]

How did you install OpenCV ?
Did you check that it is from the correct architecture ?

[georgiav]

@SGaist I was checking now, I'm using it from the virtual machine provided by my university. The path seemed fine when I was compiling the program from a shell so I'm not sure what's wrong. What should I look for ?

[SGaist]

Call "file /usr/local/lib/libopencv_core.so". What do you get ?

As for your .pro file:

LIBS += -L/usr/local/lib \
        -lopencv_core \ 
        -lopencv_highgui \
        -lopencv_imgproc

should be enough to link to these OpenCV libraries.

[georgiav]

@SGaist It was a 'symbolic link' to libopencv_imgproc.so.4.5.0, so I called it again for that and got:
file /usr/local/lib/libopencv_imgproc.so.4.5.0
/usr/local/lib/libopencv_imgproc.so.4.5.0: ELF 64-bit LSB shared object, x86-64, version 1 (GNU/Linux), dynamically linked, BuildID[sha1]=a9e4463d8bcc7f5051819e1ab34a131be7685cb3, not stripped

[SGaist]

Can you show your current .pro file content ?

[georgiav]

@SGaist yes :
QT += core gui
greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

   CONFIG += c++11
   
   # You can make your code fail to compile if it uses deprecated APIs.
   # In order to do so, uncomment the following line.
   #DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000    # disables all the APIs deprecated before Qt 6.0.0
   
   SOURCES += \
       core.cpp \
       main.cpp \
       mainwindow.cpp
   
   HEADERS += \
       mainwindow.h
   
   FORMS += \
       mainwindow.ui
   
   INCLUDEPATH += -I/usr/local/include
   LIBS += -L/usr/local/lib \
           -lopencv_core \
           -lopencv_highgui \
           -lopencv_imgproc
   
   # Default rules for deployment.
   qnx: target.path = /tmp/$${TARGET}/bin
   else: unix:!android: target.path = /opt/$${TARGET}/bin
   !isEmpty(target.path): INSTALLS += target

[SGaist]

That looks good. What exact error are you getting now, after doing a full rebuild ?

[georgiav]

[SGaist]

That's not a linking problem you have there.

Where is opencv2/core.hpp located exactly in your system ?

[georgiav]

it should be the one on top left right? given the path

[SGaist]

Did you notice the "opencv4" folder that is missing from your INCLUDEPATH statement ?

Either add it there or to your include statements.

[georgiav]

I tried that and it still doesn't work apparently

[SGaist]

Please provide the information directly.
What exactly did you try ?
What is the error your get ?

[georgiav]

I changed the include statements to that and in the .pro file the INCLUDEPATH is /usr/local/include/opencv4

[SGaist]

@SGaist said in Why after linking the OpenCV libraries, Mat objects are still 'undefined'?:

Did you notice the "opencv4" folder that is missing from your INCLUDEPATH statement ?

Either add it there or to your include statements.

I wrote "either" which means one or the other, not both.

[georgiav]

So I changed it in the main.cpp file because otherwise I got those errors . Now in the .pro file is /usr/local/include.
I still get the same errors

The last error I don't understand because I wrote opencv2/core/core.hpp not opencv2/core.hpp and I cleaned the project again before