“App termination due to uncaught exception” on iOS

Question

There is one for loop in my code. When this loop continues, my application crashes and prints the following message to the console:

 Terminating app due to uncaught exception 'NSRangeException', reason: '-[NSMutableArray objectAtIndex:] index 2 beyond bounds [0 .. 1]' Call stack at first throw: 

Using this for loop, I am trying to populate NSMutableArray , but that is not what is being done.

Answer 1

This usually happens when you try to access an element with an index outside the borders of NSArray .

So say you had NSArray :

 NSArray *a = [NSArray arrayWithObjects:@"a", @"b", @"c", nil]; 

This code will print “Array Index Outside of Borders” because the borders are 0 - 2:

 @try { NSString *string = [a objectAtIndex:3]; } @catch(NSRangeException *e) { NSLog(@"Array index out of bounds"); } 

The best way to solve this problem is to use a quick enumeration :

 for(id obj in array) { //do something with obj } 

Fast enumeration uses an enumerated implementation of the NSFastEnumeration protocol NSFastEnumeration to handle all the dirty work for you.

One thing that usually causes this problem, even when using fast enumeration, is if you enumerate a mutable structure such as NSMutableArray and inside the loop body, you mutate the structure using removeObject: or its variants, you will encounter this exception earlier than later, because the length of the structure is cached, and therefore it will continue until the next iteration, even if it goes beyond.

But using a quick enumeration, you will catch this error pretty quickly, because the internal __NSFastEnumerationMutationHandler will catch it and throw the following exception:

 2011-02-11 00:30:49.825 MutableNSFastEnumerationTest[10547:a0f] *** Terminating app due to uncaught exception 'NSGenericException', reason: '*** Collection <NSCFArray: 0x10010c960> was mutated while being enumerated.<CFArray 0x10010c960 [0x7fff70c45ee0]>{type = mutable-small, count = 2, values = ( 0 : <CFString 0x100001078 [0x7fff70c45ee0]>{contents = "b"} 1 : <CFString 0x100001058 [0x7fff70c45ee0]>{contents = "c"} )}' *** Call stack at first throw: ( 0 CoreFoundation 0x00007fff8621e7b4 __exceptionPreprocess + 180 1 libobjc.A.dylib 0x00007fff80daa0f3 objc_exception_throw + 45 2 CoreFoundation 0x00007fff862765bf __NSFastEnumerationMutationHandler + 303 3 MutableNSFastEnumerationTest 0x0000000100000de7 main + 295 4 MutableNSFastEnumerationTest 0x0000000100000cb8 start + 52 5 ??? 0x0000000000000001 0x0 + 1 ) terminate called after throwing an instance of 'NSException' 

Answer 2

Your exception implies that you are trying to access something out of range in your array (index 2 is out of bounds). If you just need to access the array, it is best to use a fast enumeration (for each loop).

 for (NSString *str in array) NSLog(@"%@", str); 

Something like this will protect against any exceptions from outside.

Answer 3

The type of exception is called the index of the associated exception. This usually happens when you try to access an element of an array that is not there.