Memory Management in Objective-C [duplicate]

Answer 1

Here are the rules:

1. If you create an object by calling alloc or copy, you own it and must release it when you're done.
2. If you didn't create an object, but want it to ensure it sticks around before control returns to the run loop (or, to keep things simple, your method returns), send it a retain message and then release it later when you're done.
3. If you create an object and want to return it from your method, you are obligated to release it, but you don't want to destroy it before the caller gets a chance to see it. So you send it autorelease instead, which puts it in the Autorelease Pool, which is emptied once control gets back to the program's event loop. If nobody else retains the object, it will be deallocated.

Regarding arrays, you are free to do something like this:

NSObject *threeObjects[3];

threeObjects[0] = @"a string";
threeObjects[1] = [NSNumber numberWithInt:2];
threeObjects[2] = someOtherObject;

Reasons to use NSArray anyway:

• NSArray will take care of retaining objects as you add them and releasing them as you remove them, whereas in a plain C array you will have to do that yourself.
• If you are passing an array as a parameter, an NSArray can report the count of objects it contains, with a plain C array you'll need to pass a count along too.

• Mixing square bracket meanings on one line feels weird:

  [threeObjects[0] length]