Objc 中 nil Nil NULL NSNull 之间的区别
07 Jun 2015nil
#ifndef nil
#define nil __DARWIN_NULL /* id of Nil instance */
#endif
Nil
#ifndef Nil
#define Nil __DARWIN_NULL /* id of Nil class */
#endif
NULL
#ifndef NULL
#define NULL __DARWIN_NULL
#endif /* ! NULL */
NSNull
NSNull is a class defines a singleton object used to represent null values in collection objects (which don’t allow nil values).
[NSNull null]: The singleton instance of NSNull.
#import <Foundation/NSObject.h>
@interface NSNull : NSObject <NSCopying, NSCoding>
+ (NSNull *)null;
@end