Question

I’m happily using C++ objects in both, objective C++ (.mm) header and implementation files as well as call into Objective C(++) classes from my C++ implementation files, but every attempt to use Objective C classes in the C++ header file results in compiler errors.

Stuff like this class declaration fails to compile:

class CQuartzTextRenderer {

public:
                 CQuartzTextRenderer();
 virtual        ~CQuartzTextRenderer();
 virtual void    Render(CDrawingOptions &inDrwOpt);


private:

  NSFont*  CreateNSFontForFontName(string &fontName, int fontSize);
};

no matter what (AppKit/..) includes I’ve tried.
Any ideas?

Answer 1

You can’t have an Objective-C class inside a header file that is included by a .cpp simply because XCode will use the standard g++ compiler and treat the file as plain C++.

To fix these errors (and be allowed to use Objective-C classes in header files) you must make sure that header file is included ONLY by .mm files, not in any .cpp.

Just an addition: it may happen that you actually have a foobar.h coupled with foobar.mm. This is correct and allows you to have Objective-C in the header file but if that file is included somewhere else by a .cpp or by another .h which is included by a .cpp then you’ll get compilation errors. Mind that every unit is compiled independently from others.