Using @import in objective C in conjunction with __cplusplus

Question

When I try to compile an Objective C++ file (.mm) that is linked to a file that uses the new @import directive, I get some errors. Currently, my only solution is to replace the @import with the old #import directive.

Is there any other solution so I can still use @import?

Build failed "Unexpected '@' in program" – Mihai Popa Dec 20 '13 at 17:11 — Mihai Popa, Dec 20 '13 at 17:11

Ivan Genchev · Accepted Answer · 2017-10-03T09:03:13.220

22

Edit: According to the latest docs this should work now.

See this. You have to use the -fcxx-modules flag instead of the -fmodules flag, but as the official documentation suggests - EXPERIMENTAL and VERY BROKEN. I didn't manage to get it working at all... In my opinion it's better to stick with #import and #include until that feature is out of experimental stage.

From clang.llvm.org:

-fcxx-modules
    Enable the modules feature for C++ (EXPERIMENTAL and VERY BROKEN).

edited Oct 03 '17 at 09:03

answered Dec 20 '13 at 17:13

Ivan Genchev

2,746
14
25

@kevlar that answer was from more than three years ago.. According to the docs it should work now. Haven't tried it myself yet, though. – Ivan Genchev Jun 13 '17 at 20:41
1

Sorry for the dull question but where do you set this flag – Stan Sep 13 '17 at 12:03
@IvanGenchev The documentation is update. Could you please update your answer? – bikram990 Sep 24 '17 at 08:54
Can you please help me that where do you set this flag in xcode ? – Maulik Kundaliya Jun 09 '18 at 11:20
2

I added it to `Build Settings` -> Other C++ Flags and compiled with me. – Elsammak May 13 '19 at 05:25

MMSousa · Answer 2 · 2020-06-07T14:33:25.663

In my case I needed to use OpenCV in my application.

I have solved this problem by adding

-fcxx-modules (Objective C++) manually to "Other C++ Flags"

(Build Settings/ Apple Clang - Custom Compiler Flags/ Other C++ Flags)

or

-fmodules (Objective C) to "Other C Flags"

(Build Settings/ Apple Clang - Custom Compiler Flags/ Other C Flags)

And also I needed to put import the opencv.hpp before any Apple's headers to fix errors of Expected identifier in opencv library. For example in Prefix.pch I organized it that way:

#ifdef __cplusplus
#include <opencv2/opencv.hpp>
#endif

#import <Availability.h>

I am using:

Xcode - 11.3
CocoaPods - 1.9.1
OpenCV2 - 4.3.0

Using @import in objective C in conjunction with __cplusplus

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