Meaning of symbol ^ in Objective C

Question

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Caret in objective C
What does this ^ syntax mean in Objective-C?

I am tired by searching the meaning of symbol ^ in Objective C. I have seen it in lot of projects especially in back ground running tasks. I will put a link http://developer.apple.com/library/ios/#samplecode/StitchedStreamPlayer/Introduction/Intro.html#//apple_ref/doc/uid/DTS40010092 and in MyStreamingMovieViewController.m you can find the following inside - (IBAction)endScrubbing:(id)sender method.

timeObserver = [[player addPeriodicTimeObserverForInterval:CMTimeMakeWithSeconds(tolerance, NSEC_PER_SEC) queue:dispatch_get_main_queue() usingBlock:
                         ^(CMTime time)
                         {
                             [self syncScrubber];
                         }] retain];
    }

Also http://developer.apple.com/library/ios/#documentation/iphone/conceptual/iphoneosprogrammingguide/ManagingYourApplicationsFlow/ManagingYourApplicationsFlow.html

- (void)applicationDidEnterBackground:(UIApplication *)application
{
UIApplication*    app = [UIApplication sharedApplication];

bgTask = [app beginBackgroundTaskWithExpirationHandler:^{
    // Clean up any unfinished task business by marking where you.
    // stopped or ending the task outright.
    [app endBackgroundTask:bgTask];
    bgTask = UIBackgroundTaskInvalid;
}];

// Start the long-running task and return immediately.
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

    // Do the work associated with the task, preferably in chunks.

    [app endBackgroundTask:bgTask];
    bgTask = UIBackgroundTaskInvalid;
});
}

Please let me know the answer.

Answer 1

That symbol is used to declare block.

For more information read here Blocks Programming Topics

Some more info:

Block objects are a C-level syntactic and runtime feature. They are similar to standard C functions, but in addition to executable code they may also contain variable bindings to automatic (stack) or managed (heap) memory. A block can therefore maintain a set of state (data) that it can use to impact behavior when executed.

You can use blocks to compose function expressions that can be passed to API, optionally stored, and used by multiple threads. Blocks are particular useful as a callback because the block carries both the code to be executed on callback and the data needed during that execution.