Basic Question about iPhone Object C Arrays and Deep and Pointer Copy

I am new to the iPhone / Mac space and this is probably a pretty basic question, I have done some searching and have not found the direct answer.

I would like to know if the addObject method for Arrays / Mutable Arrays does a shallow (pointer only) or deep (copies object) when adding.

1. A mutable array that has been alloc
2. A 开发者_开发技巧NSString that has been alloc with some sort of init
3. We addObject the string to the mutable array
4. We then release the NSString

If this is the proper way to do things, that it is assumed that the addObject will do a deep copy of the NSString. Just confirming that this is the proper way to do memory management with mutable array ...

addObject: does a shallow copy. What you're missing is that NSMutableArray retains the object, so it does not go away, but does not require a deep copy. This is a key point to Objective-C memory management. You should read the Memory Management Programming Guide. Cocoa memory management is not complicated, and is incredibly consistent. I have a shortened summary at Three Magic Words.

When adding an Object to an Array, its retain count will be increased. A object will be released when its retain count is 0. So when adding the NSString to you anArray it won't be a copy (you can change foo and it will be changed in the array, too) but it will increase foo's retain count by 1.

NSString *foo = [[NSString alloc] initWithString@"bar"]; // retain count +1
[anArray addObject:foo]; // NOT COPIED, but retain count of 'foo' increased by 1
[foo release]; // retain count of foo decreased by 1

When you at some time release anArray, it will call release on its objects. So foo's retain count will finally become 0 and foo will be released.

// some time later..
[anArray release]; // anArray released, foo retain count = 0.. foo gets released.

Kind Regards, Christian