Would a pointer to a pointer to nil match against NULL?

Question

Example:

A validation method contains this check to see if an NSError object shall be created or not:

- (BOOL)validateCompanyName:(NSString *)newName error:(NSError **)outError {
    if (outError != NULL) {
        // do it...

Now I pass an NSError object, like this:

NSError *error = nil;
BOOL ok = [self validateCompanyName:@"Apple" error:&error];

I'm not sure if this matches the check for not NULL. I think it's not NULL, since I believe NULL is not nil. Maybe someone can clear this up?

Answer 1

nil (all lower-case) is a null pointer to an Objective-C object.

Nil (capitalized) is a null pointer to an Objective-C class.

NULL (all caps) is a null pointer to anything else.

Yet they all compile to 0, so (nil == Nil == NULL == 0) (thanks Dave).