Is it possible to set an object to null

Question

Further in my code  I check to see check if an object is null empty   Is there a way to set an object to null

User · Answer

An object of a class cannot be set to NULL; however, you can set a pointer (which contains a memory address of an object) to NULL.

Example of what you can't do which you are asking:

Cat c;
c = NULL;//Compiling error

Example of what you can do:

Cat c;
//Set p to hold the memory address of the object c
Cat *p = &c;
//Set p to hold NULL
p = NULL;

User · Answer

You want to check if an object is NULL empty  Being NULL and empty are not the same  Like Justin and Brian have already mentioned  in C   NULL is an assignment you d typically associate with pointers  You can overload operator  perhaps  but think it through real well if you actually want to do this  Couple of other things     In C   NULL pointer is very different to pointer pointing to an  empty  object   Why not have a bool IsEmpty   method that returns true if an object s variables are reset to some default state  Guess that might bypass the NULL usage  Having something like A  p   new A      p   NULL  is bad  no delete p  unless you can ensure your code will be garbage collected  If anything  this d lead to memory leaks and with several such leaks there s good chance you d have slow code   You may want to do this class Null     Null  NULL  and then overload operator  and operator   of other classes depending on your situation     Perhaps you should post us some details about the context to help you better with option 4   Arpan

User · Answer

an object  of what type    You can certainly assign NULL  and nullptr  to objects of pointer types  and it is implementation defined if you can assign NULL to objects of arithmetic types    If you mean objects of some class type  the answer is NO  excepting classes that have operator  accepting pointer or arithmetic types    empty  is more plausible  as many types have both copy assignment and default construction  often implicitly   To see if an existing object is like a default constructed one  you will also need an appropriate bool operator

User · Answer

While it is true that an object cannot be  empty null  in C    in C  17  we got std  optional to express that intent   Example use   std  optional lt int gt  v1           empty  int std  optional lt int gt  v2 3        Not empty   contains a 3    You can then check if the optional contains a value with  v1 has value       false   or  if v2           You get here if v2 is not empty     A plain int  or any type   however  can never be  null  or  empty   by your definition of those words  in any useful sense  Think of std  optional as a container in this regard   If you don t have a C  17 compliant compiler at hand  you can use boost optional instead  Some pre-C  17 compilers also offer std  experimental  optional  which will behave at least close to the actual std  optional afaik  Check your compiler s manual for details

User · Answer

You can set any pointer to NULL  though NULL is simply defined as 0 in C     myObject  foo   NULL    Also note that NULL is defined if you include standard headers  but is not built into the language itself   If NULL is undefined  you can use 0 instead  or include this    ifndef NULL  define NULL 0  endif   As an aside  if you really want to set an object  not a pointer  to NULL  you can read about the Null Object Pattern

[c++] Is it possible to set an object to null?

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