Question

I need to generate a UUID string in some code with ARC enabled.

After doing some research, this is what I came up with:

CFUUIDRef uuid = CFUUIDCreate(NULL);
NSString *uuidStr = (__bridge_transfer NSString *)CFUUIDCreateString(NULL, uuid);
CFRelease(uuid);

Am I correctly using __bridge_transfer to avoid leaking any objects under ARC?

Answer 1

Looks fine to me. This is what I use (available as a gist)

- (NSString *)uuidString {
    // Returns a UUID

    CFUUIDRef uuid = CFUUIDCreate(kCFAllocatorDefault);
    NSString *uuidString = (__bridge_transfer NSString *)CFUUIDCreateString(kCFAllocatorDefault, uuid);
    CFRelease(uuid);

    return uuidString;
}

Edited to add

If you are on OS X 10.8 or iOS 6 you can use the new NSUUID class to generate a string UUID, without having to go to Core Foundation:

NSString *uuidString = [[NSUUID UUID] UUIDString];
// Generates: 7E60066C-C7F3-438A-95B1-DDE8634E1072

But mostly, if you just want to generate a unique string for a file or directory name then you can use NSProcessInfo‘s globallyUniqueString method like:

NSString *uuidString = [[NSProcessInfo processInfo] globallyUniqueString];
// generates 56341C6E-35A7-4C97-9C5E-7AC79673EAB2-539-000001F95B327819

It’s not a formal UUID, but it is unique for your network and your process and is a good choice for a lot of cases.