When should I use nil and NULL in Objective-C?
问题 This is sample code: NSDictionary *myDictionary = [NSDictionary dictionary]; NSNumber *myNumber = [myDictionary valueForKey: @\"MyNumber\"]; NSLog(@\"myNumber = %@\", myNumber); // output myNumber = (null) if (myNumber == nil) NSLog(@\"test 1 myNumber == nil\"); if (myNumber == NULL) NSLog(@\"test 2 myNumber == NULL\"); if ([myNumber isEqual:[NSNull null]]) NSLog(@\"test 3 myNumber == [NSNull null]\"); When should I use nil, NULL and [NSNull null]? 回答1: You can use nil about anywhere you can