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I’m not really sure what to call this title. This might be a retain count problem I’m dealing with. I’ll try to describe the problem. Here is a section of code that calls the method “findLongestRoad:throughIntersection:” twice. I pass a NSMutableArray object both times. (POSITIVE and NEGATIVE are just two integer #define tags and aren’t relevant)

path = [[NSMutableArray alloc] init];
[r findLongestRoad:path throughIntersection:POSITIVE];
[path removeObject:r];
[r findLongestRoad:path throughIntersection:NEGATIVE];
totalRoads = [path count];
[path release];

The implementation of method “findLongestRoad” is below. At issue is confusion on my part as to what is happening with the loop at the end of the method.

When initially allocated in the debugger, path is 0x514940. The first time I call the method, path will have 2 objects, and when the “path = …arrayWithArray” is executed, path keeps the address of 0x514940, thereby passing back to the main function the 2 object array. The second time I call the method, we need to return a 3 object array. The “path = …arrayWithArray” on the second call for some reason returns a 3 object array but a different address of 0x5b7260. This would be fine, except when it returns back to the main function, the path there still retains the old address of 0x514940 and the old 2 object array.

Can someone explain why it performs differently on two different calls?

– JohnathanSteere

The pointer parameter path is passed by value and thus treated like any other local variable, the scope of the reassignment is local to the method. A solution to the problem would be to pass a pointer to the array ( NSMutableArray **path ), but considering that it looks like it is coming in pre-assigned that might not be a good idea and it would not be a good design decision for a method to release something it does not own. Another solution would be to empty the passed array and re-populate the existing object. A third approach would just return the result array (as a return value) in the case where no reassignment was needed, i.e. retain/autorelease the passed array, otherwise just return a newly created auto-released array.