Xcode 7 and openCV (no Swift): Core.hpp header must be compiled as C++

The solution is almost the same as we do bridging ObjectiveC and swift but we do it between Objective C and C++ so we put the C++ codes in a separate file with (.mm) extension and then import it to your Objective C File (.m)

For example if you have ViewController.h and ViewController.m you add two more files which include your C++ codes lets name it OpenCV.mm and OpenCV.h then import the OpenCV.h inside ViewController.m even before you import anything else. May be this image will help understand it:

Tested on Xcode 11.6 OpenCV Ver 3.4.3

I just had the exact same problem. I'm working in a Swift project with OpenCV.

Regarding Swift, its entry point to OpenCV is a file I called OpenCVWrapper. So I got OpenCVWrapper.h and OpenCVWrapper.mm. In the bridging header of my project, I got #import "OpenCVWrapper.h".

Thing is I wanted to write a class called MatUtils in Objective-C++ that I could call from OpenCVWrapper.mm. For them to be seeable in there, I had to put them in MatUtils.h.

Long story short, the mistake is that in OpenCVWrapper.h, I did #import "MatUtils.h". MISTAKE!!!! As OpenCVWrapper is in the bridging header, C++ is now reachable from Swift!

Quick fix : #import "MatUtils.h" in OpenCVWrapper.mm!

Cheers! bRo

OpenCV is a C++ framework, which means that any code that makes use of OpenCV has to be compiled with C++ interpretation, rather than C interpretation.

The errors you see, e.g. with the using namespace cv; indicate that the code is compiled using the objective-C compiler, rather than the objective-C++ compiler.

As I mentioned in my comment the easiest way to get this to happen is to ensure that any file that #includes an opencv header must be named e.g. ViewController.mm, i.e. it must be an Objective-C++ file.

Alternatively, you can select and override the Type of the file, by explicitly selecting the Objective-C++ Source option for the file type in the utilities pane.