How to return correctly a NSMutableString from a method

Question

Hi,

I'm looking for a good way to return a string constructed by a NSMutableString avoiding leaking :

eg:

+(NSString *)myMethod{



 NSMutableString *numberToReturn = [[NSMutableString alloc] init];
 [numberToReturn appendString:@"lorem ipsum"];


 return numberToReturn;
}

The leak instrument said I had leak with this variable.

I tried autorelease but it crashes I tried to return a copy or copying the mutablestring into a nsstring but leak still present.

Any idea or trick? I'have a to call this method each time the user type a value into the textfield, so the application crashes due to bad memory management...

thank you

Answer 1

You should probably return an autorelease-d variable, as you've already mentioned. Can you give more detail as to why that was crashing? Was the caller perhaps then release-ing the variable without having retain-ed it?

It also looks like you're returning an NSString* from this function, although you alloc-ed a NSMutableString, but that should be okay.

Answer 2

You should use -autorelease. Your method should be written as:

+ (NSString*)myMethod {
    NSMutableString *stringToReturn = [[NSMutableString alloc] init];
    [stringToReturn appendString:@"lorem ipsum"];

   return [stringToReturn autorelease];
}

If there is a crash, the fault is elsewhere.

Of course, you can make use of factory methods that return an already-autoreleased instance, rewritting your method as

+ (NSString*)myMethod {
  NSMutableString *result = [NSMutableString string];
  [result appendString:@"lorem ipsum"];

  return result;
}

or better yet for your example,

+ (NSString*)myMethod {
    NSMutableString *result = [NSMutableString stringWithString:@"lorem ipsum"];
    //...do something with result;
    return result;
}

Obviously if you method's only purpose is just to return a new string with a string, you can avoid the whole method all together and use [NSMutableString stringWithString:@"lorem ipsum"] if you really need a mutable string.

Answer 3

You should autorelease the string before returning it. That's what the memory management rules say to do. If your app then crashes, that's evidence of a bug somewhere else in your code.

Answer 4

does it work the same on the iPhone SDK ?