Cast of C pointer type 'void *' to Objective-C pointer type 어쩌고저쩌고 에러가 나는 경우

이전에는 이런 예러가 없었는데 이전 소스를 새 프로젝트에 넣다가 보면 이런 에러가 생기는 경우가 있다.

일단 cast 문제인데.. 당황스럽다.!!!

다음과같이해서 수정하였다..!!

결론은 캐스팅할때 __bridge 를 같이 넣자이다.!!!

ARC with C or C++ code (Chipmunk, Box2D) All is fine and well with ARC in Objective-C land. However, as soon as you also work with C or C++ code — such as the Chipmunk or Box2D libraries, or the Core Foundation framework — you may find yourself facing compiler errors. Fortunately, it's half as bad if you understand why the compiler keeps bugging you. Errors you'll see when casting id to void* and vice versa What is a "bridged cast"? Bridge casts for Core Foundation More about bridge casts Box2D & Chipmunk real-world examples Errors you'll see when casting id to void* and vice versa Most errors when working with C/C++ code has to do with the fact that you can't freely cast id to void* and vice versa. For example, the below example won't work: NSObject* myObject = [[NSObject alloc] init]; void* myObjectPointer = myObject; // ERROR   void* myObjectPointer2 = NULL; NSObject* myObject2 = myObjectPointer2; // ERROR You'll get an error like this one: error: cannot initialize a variable of type '...' with an lvalue of type '...' The types in the error message mentioned may differ but you'll see a __strong keyword thrown in for good measure. Well, you might think this can be fixed by properly casting to the correct types: NSObject* myObject = [[NSObject alloc] init]; void* myObjectPointer = (void*)myObject; // ERROR, still ...       void* myObjectPointer2 = NULL; NSObject* myObject2 = (NSObject*)myObjectPointer2; // ERROR, still ... This time the error is different, each of the two casts above generates a different message: 1: Cast of Objective-C pointer type 'NSObject *' to C pointer type 'void *' requires a bridged cast 2: Cast of C pointer type 'void *' to Objective-C pointer type 'NSObject *' requires a bridged cast What is a "bridged cast"? ARC adds the keywords __bridge, __bridge_transfer and __bridge_retained which must be used when casting. Here's the above example with a "bridged cast" that fixes the compile errors: NSObject* myObject = [[NSObject alloc] init]; void* myObjectPointer = (__bridge void*)myObject;       void* myObjectPointer2 = NULL; NSObject* myObject2 = (__bridge NSObject*)myObjectPointer2; The use of __bridge in the cast tells the compiler that the object's lifetime doesn't change, and that you understand that if the object's memory is released it may result in a dangling pointer and a potential crash. This is the same behavior to non-ARC code, but ARC really wants to make sure you understand the implications and potential dangers. In ARC terms, you specify that the cast creates a "unsafe unretained" reference. Bridge casts for Core Foundation When interfacing with Core Foundation you may want to use __bridge_retain to tell ARC to take on ownership of the object (retain it). Likewise, __bridge_transfer tells ARC to release the object after the expression. Do not apply retain or transfer bridge casts to objects that are not Core Foundation (CF) objects! More about bridge casts For more details about bridged casts read the section about Bridged Casts and the follow-up section Conversion of retainable object pointers in the LLVM compiler documentation. Box2D & Chipmunk real-world examples CCSprite* aSprite = [CCSprite spriteWithFile:@"image.png"];     // Assigning sprite to Box2D userdata b2BodyDef bodyDef; bodyDef.userData = (__bridge void*)aSprite;   // Getting the userdata sprite from Box2D CCSprite* sprite = (__bridge CCSprite*)body->GetUserData();     // Assigning sprite to Chipmunk userdata cpShape* shape = cpPolyShapeNew(staticBody, numVertices, vertices, offset); shape->data = (__bridge void*)aSprite;   // Getting the userdata sprite from Chipmunk CCSprite* sprite = (__bridge CCSprite*)shape->data;

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