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

[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

[jsulm]

@georgiav Change INCLUDEPATH in your pro file so, that it points to /usr/local/include/opencv4 and change your includes like

#include "opencv2/...

[georgiav]

@jsulm Hi, I tried that before and I got those errors of 'file not found' ( photo above)

[SGaist]

Here is a minimal example adjusted to the paths you shown to us:

.pro file:

TEMPLATE = app
TARGET = test_opencv
INCLUDEPATH += .
INCLUDEPATH += /usr/local/include/opencv4
 
LIBS += -L/usr/local/lib/ -lopencv_core
SOURCES += main.cpp

main.cpp:

 #include <opencv2/core.hpp>
  
 int main(int argc, char **argv)
 {
      cv::Mat mat;
      return 0;
 }

[georgiav]

@SGaist Yes, this seems to work fine! Thank you very much!