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Anna Koneva

Dr. Dobb's Bloggers

Calling an Objective-C Method from a C++ Class

February 14, 2014

Let's say you have the following Objective-C class and you want to access it from C++:

@interface ObjC : NSObject

- (int)someObjCMethod:(int)param;


@implementation ObjC

- (int)someObjCMethod:(int)param
    NSLog(@"param = %i", param);
    return param;


You might use the code in CppClass.cpp, shown here, for access:

class CppClass
        int someMethod(int param);

But if you do, you'll get a lot of compilation errors like these (from Clang):

… Expected unqualified-id
… Unknown type name 'NSString'
… Unknown type name 'Protocol'


A solution to the problem is to rename this last file from CppClass.cpp to CppClass.mm. This will turn the C++ class into Objective-C++ and will do exactly what you need. Both GCC and Clang will see the new file correctly and allow the interoperation to work as expected.

Anna Koneva is a software engineer from Moscow, Russia. Her areas of interest and work include programming languages, especially C++, C#, and Objective-C. She develops desktop applications for Windows and mobile applications for the iPhone and iPad.

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