Question

I have been coding application from past 1 year, However first time I came across a weird looking selector argument,

- (NSString *)dictionaryForString:(NSDictionary *)dictionary error:(NSError **)error

As you can see (NSDictionary *) is with one asterisks and (NSError **) with two, So what is the difference between having one or two asterisks?

Thanks

Answer 1

This method returns an error by reference, that is, you pass it an address of a pointer to an NSError and it (optionally) sets the pointer value.

NSError *error = nil;
NSString *result = [obj dictionaryForString: dict error: &error];
if (!result)
    NSLog(@"%@", error);

This is a common C practice.