Question

In the tutorial there is the following declaration:

-(BOOL)writeToFile:(NSString *)path atomically:(BOOL)useAuxiliaryFile;

I’m interpreting this as writeToFile method returns a BOOL result. It takes 2 parameters. The first is an NSString reference. The second is the result of calling atomically and passing it a BOOL value.

Did I get that right?

The tutorial goes on to say you call the above method like this:

BOOL result = [myData writeToFile:@"/tmp/log.txt" atomically:NO];

which is find. But I wonder if I MUST use “atomically:NO”

Could I have done something like

resultOfAtomically = atomically:NO
BOOL result = [ myData writeToFile:@"/tmp/log.txt" resultOfAtomically ];

assuming I declared resultOfAtomically properly.

Also, does prepending @ to "/tmp/log.txt" mean something like “give me the reference NOT the value” ?

Answer 1

The text atomically introduces the second parameter of the writeToFile:atomically: method, it is not a separate function. Therefore, you cannot call simply atomically:NO. This would be correct, however:

BOOL myBool = NO;

BOOL result = [myData writeToFile:@"/tmp/log.txt" atomically:myBool];

When talking about Objective-C methods, you would not call this method “writeToFile”, you would call it “writeToFile:atomically:”. By this syntax you know that the method expects two parameters (one for each colon).

Here’s a way to think about how the method declaration breaks down:

-(BOOL)writeToFile:(NSString *)path atomically:(BOOL)useAuxiliaryFile;

- = defining an instance method (+ would be for a class method).

(BOOL) = returning a boolean value.

write = this method is about writing something (nothing magic, just a friendly word choice – could have been print or something else).

ToFile:(NSString *)path = the first parameter of the method, path, is an NSString pointer and the friendly text “ToFile” (again just a word choice, nothing special) hints that I need to provide a file path for that parameter.

atomically:(BOOL)useAuxiliaryFile; = the second parameter of the method, useAuxiliaryFile, is a boolean and the friendly text “atomically” (still nothing special) hints that the boolean value determines whether or not to write the file atomically.