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    <p>The problems is here:</p> <pre><code> CFStringRef cfUuid = CFUUIDCreateString(NULL, CFUUIDCreate(NULL)); deviceUuid = (NSString *)cfUuid; CFRelease(cfUuid); [defaults setObject:deviceUuid forKey:@"deviceUuid"]; </code></pre> <p>Let's go through what this actually does:</p> <pre><code> CFStringRef cfUuid = CFUUIDCreateString(NULL, CFUUIDCreate(NULL)); </code></pre> <p>A CFUUID is created (and leaked). A CFStringRef is created and assigned to cfUuid. (Note: The name cfUuid implies that cfUuid is a CFUUIDRef. Of course, it isn't; it's a CFStringRef.)</p> <pre><code> deviceUuid = (NSString *)cfUuid; </code></pre> <p>That same CFStringRef is <em>type cast</em> and assigned to deviceUuid. This is <strong>not</strong> a new instance of NSString or CFStringRef, it's just a typecast of the <strong>same</strong> instance.</p> <pre><code> CFRelease(cfUuid); </code></pre> <p>You release the CFStringRef. Since the NSString points to the same object, you also release it.</p> <pre><code> [defaults setObject:deviceUuid forKey:@"deviceUuid"]; </code></pre> <p>And here, you use the typecasted object, which was released before.</p> <p>THe simplest fix to the stale pointer is this:</p> <pre><code> CFStringRef cfUuid = CFUUIDCreateString(NULL, CFUUIDCreate(NULL)); deviceUuid = (NSString *)cfUuid; [defaults setObject:deviceUuid forKey:@"deviceUuid"]; CFRelease(cfUuid); </code></pre> <p>But this code is dangerous, and you already know why: deviceUuid is also invalid. But this isn't obvious, so you can trip on it later. Also, it doesn't fix the CFUUID leak.</p> <p>To fix the CFStringRef leak, you could use this:</p> <pre><code> deviceUuid = (NSString *)CFUUIDCreateString(NULL, CFUUIDCreate(NULL)); [defaults setObject:deviceUuid forKey:@"deviceUuid"]; [deviceUuid autorelease]; // or release, if you don't need it in code not // included in your post </code></pre> <p>However, this still doesn't fix the CFUUID leak.</p> <pre><code> CFUUIDRef cfuuid = CFUUIDCreate(NULL); deviceUuid = (NSString *)CFUUIDCreateString(NULL, cfuuid); CFRelease(cfuuid); [defaults setObject:deviceUuid forKey:@"deviceUuid"]; [deviceUuid autorelease]; // or release, if you don't need it in code not // included in your post </code></pre>
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    1. USSteven Fisher
    1. USSteven Fisher
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    1. COThank you for your reply. In your first example, the same message but on the line CFStringRef cfUuid = CFUUIDCreateString(NULL, CFUUIDCreate(NULL)); The second example shows the same line, here's a screenshot http://img849.imageshack.us/img849/8519/20120401215928.png
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    2. COOops. I'll have to revise the answer a bit. Thanks for pointing that out.
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    3. CODone. I should also point out that this is a great place to learn **Objective C Categories**, if you're so inclined. All of this code can be written in a category.
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