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POautoreleasing NSString in class method causing app crash in iOS
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copied!<p>The error I receive is as follows:</p> <pre><code>int main(int argc, char *argv[]) { NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init]; int retVal = UIApplicationMain(argc, argv, nil, nil); //breakpoint that says Thread 1: Program Received Signal: "EXC_BAD_ACCESS". [pool release]; return retVal; } </code></pre> <p>My two questions can be found at the bottom of this post :)</p> <p>I am currently working on an assignment for an iOS programming class and have hit a road bump. </p> <p>I have found a fix, shown below, but it doesn't make sense to me. Check it out:</p> <pre><code>@implementation MyClass // This class method takes an (NSMutableArray *) and returns an NSString with its contents printed out. + (NSString *)myString:(NSMutableArray)anArray { // NSString *myString = [[NSString alloc] init]; OLD CODE THAT CAUSES MEMORY LEAK NSString *myString = [[[NSString alloc] init] autorelease]; //NEW CODE THAT RELEASES FIRST ALLOCATION OF myString WHEN THE FIRST stringByAppendingFormat: IS CALLED NSString *vp = VARIABLE_PREFIX; //#defined above to be @"% for (id object in anArray) { if ([object isKindOfClass:[NSString class]]) { if ([object hasPrefix:vp]) { myString = [myString stringByAppendingFormat:@"%@",[object substringFromIndex:1]]; }else{ myString = [myString stringByAppendingFormat:@"%@",object]; } }else if ([object isKindOfClass:[NSNumber class]]) { myString = [myString stringByAppendingFormat:@"%@",object]; } } return myString; //shouldn't I autorelease myString right before this line? NO NOT ANY MORE. THIS myString IS NOT THE ORIGINAL THAT I alloc-init, BUT AN AUTORELEASED OBJECT RETURNED BY THE stringByAppendingFormat: message. } </code></pre> <p>When I try to send the message <code>[myString autorelease];</code>, the program crashes with the above error. It is working fine now as shown above, but I do not understand why.</p> <p>Every time I send a message containing the "magic words" <code>alloc, init, copy</code> I have to call <code>release</code>, it don't I? Or are the rules different in a Class method (can the Class itself own a file?). I do not call <code>retain</code> in the object that is calling this file.</p> <h1>Here are my two questions:</h1> <ol> <li><p>Why does this crash when I try to release <code>theDescription</code> using <code>autorelease</code>?</p></li> <li><p>Does my code create a memory leak?</p></li> </ol> <p>This is my very first question on stack overflow! Thank you for your help!</p>

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