- (NSString *)instanceMethod

Question

Dear iPhone Developers, I have an instance method which is meant to return a string

- (NSString *)newFile:(NSString *)inFile andFileNumber:(NSInteger)aNumber {
    return [NSString stringWithFormat:@"%@.o%i",inFile,aNumber];
}

I call this method as

outputFileName = [self newFile:inputFileName andFileNumber:newNumber];
// where inputFileName is a string and newNumber is an integer 
// outputFileName (also a string), inputFileName and newNumber are declared in
// the interface and in the implementation

When I compile the project with Analyzer, it gives the following messages;

1. Method returns an Objective-C object with a +0 retain count (non-owning reference)
2. Object returned to caller with a +0 (non-owning) retain count
3. Object with +0 retain counts returned to caller where a +1 (owning) retain count is expected

Also when it tries to release outputFileName the application crashes. Does somebody has any clue what is going wrong? Thanks in advance.

Answer 1

The problem is an assumption of convention. Specifically, the static analyzer assumes that any method that starts with new returns a retained object. This is because the system APIs follow this convention.

Rename your method; fileNameWithBase:fileNumber: comes to mind.

Answer 2

You're returning an autoreleased string. If you're sending it an additional -release or -autorelease message, your app will crash the next time it tries to access that string.

You should take the time to read the "memory management" section of Apple's developer documentation.

Answer 3

Your method starts with "new" with the analyzer assumes means that you want to return an object with a +1 retain count. Change the name of the method and the warnings should go away.

Also: the method returns an autoreleased object; you shouldn't be releasing it yourself.