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POBad Access Error when trying to pass error through functions
 

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  1. POBad Access Error when trying to pass error through functions
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    <p>I am trying to implement some Errorhandling in my class. I don't think I have a full understanding of how Dealing with Errors works, but I noticed that people advised, to declare Errors in functions as (<code>NSError *__autoreleasing *error</code>) so I did that. I have problems passing the error through functions.</p> <p>The following problem happens: breaking it down it seems like the following makes problems: (Sorry, the actual code is too long but I tried to extract hopefully the most important for the problem! I hope my scope of code contains the problem)</p> <p>Imagine you have <strong>ObjectA</strong> with the method:</p> <pre><code> -(NSString *) do1: (NSString *) withstuff error:(NSError *__autoreleasing *)error{ //... //error happens *error = [[NSError alloc] initwithDomain: domain code: blah userinfo: infodict]; return nil; } -(BOOL) do2error:(NSError *__autoreleasing *)error{ NSString *doesntmatter = [self do1: @"whatever" error: error]; if (doesntmatter == nil){ return NO; } } </code></pre> <p>Now in another class (AppDelegate Object) I call the following:</p> <pre><code> ObjectA* ob1 = [[ob1 alloc] init]; NSError *errorBoom = nil; if ([ob1 do2error:&amp;errorBoom] == NO){ NSLog(@"error: %@",errorBoom); //---&gt; bad access error } </code></pre> <p>It seem like errorBoom is not accessible anymore? Is that because of "__autoreleasing", I tried to understand what it actually means but all explanations so far where not very useful for me since I am very new in this field... I hope you can help me on this!</p> <p><strong>EDIT:</strong></p> <p>Ok, I think I tracked down the error. Now I know what causes it but I don't know why exactly. I wrote an simple example application that extracts the main origin of the "Bad Access"-Error occurrence:</p> <pre><code> - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions (NSDictionary *)launchOptions { self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]]; // Override point for customization after application launch. NSError *errtest = nil; BOOL testBool = [self messaroundwitherr:&amp;errtest]; NSLog(@"Filled NSError? : %@",errtest); //&lt;--Causes Bad Access. self.window.backgroundColor = [UIColor whiteColor]; [self.window makeKeyAndVisible]; return YES; } -(BOOL) giveErrornow:(NSError *__autoreleasing *)err { NSMutableDictionary *errInfo = [[NSMutableDictionary alloc] init]; [errInfo setObject:@"I feel like giving you an error!" forKey:NSLocalizedDescriptionKey]; *err = [[NSError alloc] initWithDomain:@"nonesense" code:0 userInfo:errInfo]; return NO; } -(BOOL) messaroundwitherr:(NSError *__autoreleasing *)err{ //@autoreleasepool { --&gt; uncommenting that causes the error return [self giveErrornow: err]; //} } </code></pre> <p>So apparently activating the autoreleasepool, makes the err variable be deallocated before even being able to read it from the outer function (AppFinishLaunching...). Now why is that happening exactly? I know that "@autoreleasepool" deallocates the variables after being used. In the original context I had a while loop, that's why I did it. Here it's just for comprehension reasons. So how does @"autoreleasepool" work? What happens actually with the command (*__autorelease *).</p> <p>I guess I have to fully understand the notion of it before fixing it. Does NSError (*__autorelease *) err define a "pointer to pointer of an object that is going to be autoreleased (if yes, when) " for the ARC?</p>
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    1. USDimitar Ho
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    1. CO"excess" is something else.
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    2. COWhat if you leave off the `__autoreleasing` qualifier, and just use `NSError **`?
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      1. USnielsbot
    3. CO@nielsbot I believe it is an error to not specify the lifetime qualifiers when using pointer to pointers in ARC.
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      1. USJoe
 

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