NSAutoreleasePool的官方解释
Important If you use Automatic Reference Counting (ARC), you cannot use autorelease pools directly. Instead, you use @autoreleasepool blocks instead. For example, in place of:

NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init; // Code benefitting from a local autorelease pool. [pool release];

you would write:

@autoreleasepool { // Code benefitting from a local autorelease pool. }

@autoreleasepool blocks are more efficient than using an instance of NSAutoreleasePool directly; you can also use them even if you do not use ARC.

xcode4.3引入ARC，release这块就有些变化，当你使用ARC，就必须将NSAutoreleasePool的地方换成 @autoreleasepool

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