What is the better way of handling temporary strings?

Question

I have a situation where I need to use some strings temporarily but I've read so many conflicting things that I'm a bit confused as to what the best way to proceed is.

I need to assign some strings inside an if structure but use them outside the if structure so they need to be created outside the if, I was thinking something like:

NSString *arbString = [[NSString alloc] init];

if(whatever)
{
    arbString = @"Whatever"
}
else
{
    arbString = @"SomethingElse"
}

myLabel.text = arbString;
[arbString release];

I have seen examples where people just used:

NSString *arbString;

to create the string variable

Google's Objective C guide says it's preferred to autorelease at creation time:

"When creating new temporary objects, autorelease them on the same line as you create them rather than a separate release later in the same method":

// AVOID (unless you have a compelling performance reason)
MyController* controller = [[MyController alloc] init];
// ... code here that might return ...
[controller release];

// BETTER
MyController* controller = [[[MyController alloc] init] autorelease];

So I have no idea, which is the best practice?

Answer 1

In the example you posted, you actually lose the reference to the NSString you created when you assign it in arbString = @"Whatever". You then release the string constant (which is unreleasable, by the way).

So there's a memory leak, since you never release the NSString you created.

Remember that all these types are pointers, so = only reassigns them.

As for the question, in this example, you don't need the [[NSString alloc] init]. You don't need to copy the string into a local variable anyway, you can just set myLabel.text to the string constant @"Whatever".

(edit: that's not to say that you can't use your pointer arbString, arbString = @"Whatever"; myLabel.text = arbString is fine. But this is just pointer assignment, not copying)

If you needed to manipulate the string before you returned it, you would create an NSMutableString, and either release or auto-release it. Personally, create autoreleased objects using class methods, so in this example, I'd use [NSString string], or [NSString stringWithString:], which return autoreleased objects.