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

[Matiyash]

@Matiyash I read this answer, didn't help :(
https://forum.qt.io/topic/123637/why-after-linking-the-opencv-libraries-mat-objects-are-still-undefined

[JonB]

@Matiyash
This is C++ code, why are you posting in Qt for Python forum?

I don't know anything about OpenCV. But your code shows a compilation error on the word Mat so far as I can see. That would have nothing to do with whether or not you are linking with something. It would imply you have not #included the right header file(s) or Mat is not right, e.g. perhaps it's defined in a namespace?

UPDATE
Looking at the link you just posted, by the end you can see they use cv::Mat mat;. That's just what I suggested: looks like Mat is defined in a cv:: namespace. Use cv::Mat QImage2MatColor() or maybe introduce using cv; into your file to use Mat without the namespace in front of it.

[Matiyash]

@JonB yes, I tried to include cv::, but what caused the expected namespace name error

and also why the error with the name of the function, use of undeclared identifier

[JonB]

@Matiyash
Like I said, I don't use OpenCV. Check it uses a namespace and what that name is. Maybe it's cv2 now, or opencv? Surely it gives an example somewhere?

What about trying the example at https://docs.opencv.org/3.0-beta/doc/tutorials/introduction/display_image/display_image.html (or equivalent for OpenCV 2.x if 3.0-beta is not suitable, it's what I came across Googling) to see if that works for you?

[Matiyash]

@JonB Thanks for the link, but probably not, it seems like Opencv is installed correctly, I probably have an error related to the paths to the libraries

[JonB]

@Matiyash
Since you show compilation errors only INCLUDEPATH is relevant, it has not got as far as LIBS yet. If your INCLUDEPATH were wrong you would get errors on #include lines but you do not. Your problem seems to be using namespace cv. Which is why I would test the sample code I linked, just to see whether it compiles.

[Matiyash]

@JonB well, what do you say?

[JonB]

@Matiyash
LOL, like I said, I don't use OpenCV or try that example. I know nothing about the other errors it reports. But the using namespace cv has gone through without complaint, and Mat is accepted, so you ought be able to adapt that/get it working for your code.

[jsulm]

@Matiyash The first error message basically says that std::string is an int which is very strange. Did you redefine "string" somewhere? I would not use "use namespace", at least not for cv.

[JonB]

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

Did you redefine "string" somewhere?

That seems impossible since the whole of the source file is shown, and it has nothing other than system <...> includes. And the error message states it is matching against std::string.....

The OP was only supposed to be using that sample code to get either cv::Mat or using namespace vc; Mat working.