Calling Obj-C method from C

Question

I've got a library written in C, where I need to push a call to a method written in Obj-c. I don't want to modify the original code too much, so I decided to create a "bridge" class to handle the calls between C and ObjC:

DRMBridge.h

#ifndef DRMBridge_h #define DRMBridge_h #include "DRMBridgeObjC.h" void bridge_test(); #endif

DRMBridge.c

#import "DRMBridge.h" void bridge_test() { ctest(); }

Above is compiled as C

Now here's my objc code:

DRMBridgeObjC.h

#ifndef DRMBridgeObjC_h #define DRMBridgeObjC_h #import <Foundation/Foundation.h> @interface DRMBridgeObjC : NSObject +(void) test; @end void ctest(); #endif

DRMBridgeObjC.m

#import "DRMBridgeObjC.h" @implementation DRMBridgeObjC : NSObject +(void) test { NSLog(@"OH YEAH!"); } @end void ctest() { [DRMBridgeObjC test]; }

Quite simple.

In the C library I want to call my code from I've added: #include "DRMBridge.h" into the .h file and bridge_test(); in .c file.

Now the best part, when I compile I get:

In file included from /Users/krystian/projects/mdb-reader-lib/reader-Include/ios/MDBReader/Class/DRM/DRMBridge.c:5: In file included from /Users/krystian/projects/mdb-reader-lib/reader-Include/ios/MDBReader/Class/DRM/DRMBridge.h:8: In file included from /Users/krystian/projects/mdb-reader-lib/reader-Include/ios/MDBReader/Class/DRM/DRMBridgeObjC.h:12: In file included from /Applications/Xcode64.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator8.4.sdk/System/Library/Frameworks/Foundation.framework/Headers/Foundation.h:8: /Applications/Xcode64.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator8.4.sdk/System/Library/Frameworks/Foundation.framework/Headers/NSObjCRuntime.h:400:1: error: expected identifier or '(' @class NSString, Protocol; ^ [...]

I went looking, and found this: ios - Parse Issues in NSObjCRuntime, NSZone, and NSObject

However my pch file looks like this:

#import <Availability.h> #ifndef __IPHONE_5_0 #warning "This project uses features only available in iOS SDK 5.0 and later." #endif #ifdef __OBJC__ #import <UIKit/UIKit.h> #import <Foundation/Foundation.h> #endif

I think the issue I have is that the C compiler tries to compile my ObjC file first, instead of the other way around. I've tried changing the order of files inside Compile Sources to make sure that my .m file is above .c file, but still no go.

Something else I have found which made me lost:

when I follow this answer: https://stackoverflow.com/a/20461780/487605 and change the library itself to .m, and call [DRMBridgeObjC test] code from there - it works.... Compiles fine, no errors given, works fine.

This implies to me, that there's something screwed up with my DRMBridge, but what?

Thanks Krystian

gnasher729 · Accepted Answer · 2015-10-30 08:59:34Z

1

You've seen the solution already. Use #ifdef __ OBJC__ in your Objective-C header file so that only the plain C bits are compiled when including the file from C

answered Oct 30, 2015 at 8:59

gnasher729

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2 Comments

Krystian Over a year ago

your solution works, but I'm wondering why I didn't have to go through that when I made change to the C code from the library? There was no need.

gnasher729 Over a year ago

Maybe the library did the same thing?

Cy-4AH · Accepted Answer · 2015-10-30 09:33:01Z

0

DRMBridge.h

#ifndef DRMBridge_h #define DRMBridge_h #include <CoreFoundation/CoreFoundation.h> //or put in .pch CF_EXPORT void bridge_test(); #endif

DRMBridge.m

#import "DRMBridge.h" #import "DRMBridgeObjC.h" void bridge_test() { ctest(); //or [DRMBridgeObjC test]; if you like }

Thats all. And you can include DRMBridge.h in whatever you like: in .c, in .m, in .cpp.

edited Oct 30, 2015 at 9:33

answered Oct 30, 2015 at 9:03

Cy-4AH

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6 Comments

Krystian Over a year ago

It sounds great, but I get Unknown type CF_ECTERN :/ Is there something special I should do?

Krystian Over a year ago

I'm using XCode 6.4 if that matters.

Cy-4AH Over a year ago

@Krystian, oh CF_EXPORT not CF_EXTERN.

Krystian Over a year ago

thanks, I've changed CF_EXPORT into CF_EXTERN, however still the same issue. When I add #import "DRMBridgeObjC.h" into the DRMBridge.h file, the CF_EXPORT is accepted, however I'm back to the NSObjCRuntime.h errors as described in the question.

Cy-4AH Over a year ago

Ok, you will need include CoreFoundation.h and don't put DRBridgeObjC.h in DRMBridge.h

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