When should I use nil and NULL in Objective-C

Question

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

User · Answer

To expand on a comment from  cobbal    MacTypes h contains    ifndef nil     define nil NULL  endif

User · Answer

As already mentioned  they are the same  but I use either the one or the other depending on the language in which the corresponding framework was written   For everything related to Objective-C  I use nil  For example   -  BOOL doSomethingWithObjectsInArray  NSArray   anArray       if  anArray    nil  return NO          process elements             However  when checking validity of data models from a C-framework  like AddressBook framework and CoreFoundation   I use NULL  For example   -  BOOL showABUnknownPersonVCForABRecordRef  ABRecordRef aRecord       if  aRecord    NULL  return NO          set-up the ABUnknownPersonViewController and display it on screen            This way  I have subtle clues in my code if I m dealing with Obj-C or C based code

User · Answer

In modern OS X and iOS SDKs    nil and Nil and NULL are identical in Objective-C and in Objective-C   before C  11  nil and Nil and std  nullptr are identical in Objective-C   with C  11    Stylistically  many people prefer to use nil for Objective-C objects and NULL or nullptr for other pointer types  I myself now use nil everywhere    NSNull null  is a singleton object use to represent null values in situations where nil is prohibited as a value  typically in a collection object such as an NSArray or  NSDictionary   Number and Value Programming Topics  Using NSNull

User · Answer

Basically  nil  null pointer on an object and  null  is for other type pointer

User · Answer

You can use nil about anywhere you can use null  The main difference is that you can send messages to nil  so you can use it in some places where null cant work   In general  just use nil

User · Answer

nil is an object pointer to nothing   Although semantically distinct from NULL  they are technically equivalent to one another   On the framework level  Foundation defines NSNull  which defines a class method   null  which returns the singleton NSNull object  NSNull is different from nil or NULL  in that it is an actual object  rather than a zero value   Additionally  in Foundation NSObjCRuntime h  Nil is defined as a class pointer to nothing   Refer this for further info - nil   Nil   NULL   NSNull

User · Answer

There is a difference in some contexts     Literally  Null is a character  ASCII 0     Nil is equivalent to blank  no value     Depending on the programming context  this can be a big difference

User · Answer

nil is an empty value bound corresponding with an object  the id type in Objective-C   nil got no reference address  just an empty value   NSString  str   nil    So nil should be used  if we are dealing with an object   if str  nil      NSLog  str is empty      Now NULL is used for non-object pointer  like a C pointer  in Objective-C  Like nil   NULL got no value nor address   char  myChar   NULL  struct MyStruct  dStruct   NULL    So if there is a situation  when I need to check my struct  structure type variable  is empty or not then  I will use   if  dStruct    NULL      NSLog  The struct is empty      Let   s have another example  the  -  void observeValueForKeyPath  NSString   keyPath ofObject  id object change  NSDictionary   change context  void   context   Of key-value observing  the context should be a C pointer or an object reference  Here for the context we can not use nil  we have to use NULL   Finally the NSNull class defines a singleton object used to represent null values in collection objects NSArray  NSDictionary   The  NSNull null  will returns the singleton instance of NSNull  Basically  NSNull null  is a proper object   There is no way to insert a nil object into a collection type object  Let s have an example   NSMutableArray  check     NSMutableArray alloc  init    check addObject  NSNull null     check addObject nil     On the second line  we will not get any error  because it is perfectly fair to insert a NSNull object into a collection type object  On the third line  we will get  object cannot be nil  error  Because nil is not an object

User · Answer

They both are just typecast zero s  Functionally  there s no difference between them  ie     define NULL   void  0   define nil   id 0    There is a difference  but only to yourself and other humans that read the code  the compiler doesn t care   One more thing nil is an object value while NULL is a generic pointer value

User · Answer

Use NULL for example when you invoke an Objective-C method with an output parameter of type  NSError       I see lots of example code on the web where people provide nil instead of NULL in this case  This is because it s a pointer to a pointer and thus not directly an Objective-C object type  As said above  nil should be used for Objective-C object types

User · Answer

Beware that if  NSNull null   returns true

User · Answer

nil means absence of value while NULL represent No Object   NSArray  array       Hello World      101  NSNULL null      Here  NSNULL null  is an object which means no object  at the same time you cannot add nil to indicate absence of object   you can use both nil and  NSNUll null  for checking too

User · Answer

I ve found the following   objc h   define Nil   DARWIN NULL      id of Nil class     define nil   DARWIN NULL      id of Nil instance       types h   define   DARWIN NULL   void   0    stddef h   undef NULL  ifdef   cplusplus  undef   null     VC   hack   define NULL   null  else  define NULL   void  0   endif   MacTypes h   ifndef NULL  define NULL      DARWIN NULL  endif      NULL     ifndef nil      define nil NULL  endif      nil      The way it looks  there s no difference but a conceptual one

User · Answer

NULL and nil are equal to each other  but nil is an object value while NULL is a generic pointer value   void  0  to be specific    NSNull null  is an object that s meant to stand in for nil in situations where nil isn t allowed  For example  you can t have a nil value in an NSArray  So if you need to represent a  nil   you can use  NSNull null

User · Answer

They differ in their types   They re all zero  but NULL is a void    nil is an id  and Nil is a Class pointer

User · Answer

This will help you to understand the difference between nil  NIL and null   The below link may help you in some way   http   nshipster com nil      nil -  literal null value for Objective-C objects       Nil -  literal null value for Objective-C classes       NULL -  literal null value for C pointers       NSNULL -  singleton object used to represent null

[objective-c] When should I use nil and NULL in Objective-C?

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