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    <p>The analyzer is very good at finding the routine leaks that plague new programmers writing non-ARC code (failures to call <code>release</code>, returning objects of the wrong retain count, etc.). </p> <p>In my experience, there are a couple of types of memory issues it does not find:</p> <ul> <li><p>It cannot generally identify <a href="http://developer.apple.com/library/ios/documentation/cocoa/conceptual/ProgrammingWithObjectiveC/EncapsulatingData/EncapsulatingData.html#//apple_ref/doc/uid/TP40011210-CH5-SW22">strong reference cycles</a> (a.k.a. <a href="https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/MemoryMgmt/Articles/mmPractical.html#//apple_ref/doc/uid/TP40004447-1000810">retain cycles</a>). For example, you add a repeating <code>NSTimer</code> to a view controller, unaware that the timer maintains a strong reference to the view controller, and if you don't <code>invalidate</code> the timer (or do it in the wrong place, such as the <code>dealloc</code> method), neither the view controller nor the timer will get released.</p></li> <li><p>It cannot find circular logic errors. For example, if you have some circular references where view controller A presents view controller B, which in turn presents a new copy of A (rather than dismissing/popping to get back to A).</p></li> <li><p>It cannot find many non-reference counting memory issues. While it's getting better in dealing with Core Foundation functions, if you have code that is doing manual memory allocations (such as via <code>malloc</code> and <code>free</code>), the static analyzer may be of limited use. The same is true whenever you're using non-reference counting code (e.g. you use SQLite <code>sqlite3_prepare_v2</code> and fail to call <code>sqlite3_finalize</code>).</p></li> </ul> <p>I'm sure that's not a complete list of what it doesn't find, but those are the common issues I see asked about on Stack Overflow for which the static analyzer will be of limited help. But the analyzer is still a wonderful tool (it finds issues other than memory issues, too) and for those individuals not using ARC, it's invaluable.</p> <p>Having said that, while the static analyzer is an under-appreciated first line of defense, you really should use Instruments to find leaks. See <a href="http://developer.apple.com/library/ios/#documentation/developertools/Conceptual/InstrumentsUserGuide/MemoryManagementforYouriOSApp/MemoryManagementforYouriOSApp.html">Locating Memory Issues in Your App</a> in the <em>Instruments User Guide.</em> That's the best way to identify leaks.</p>
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    1. POWhat kind of memory leaks XCode Analyzer may not notice?
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    1. USRob
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    1. COCould you illuminate a bit more why it would be bad to `invalidate` your timer in dealloc?
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      1. USMark Bernstein
    2. CO@MarkBernstein The `dealloc` is only called when there are no more strong references to the view controller. So, because the repeating timer is maintaining a strong reference to the view controller, it will never be called. Putting the `invalidate` in the `dealloc` is analogous to saying "when there are no more strong references to this view controller, go ahead and remove the timer's strong reference to this view controller." You generally put the `invalidate` in `viewWillDisappear` or something like that, depending upon the details of your app.
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