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?

Answer 1

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; 

Answer 2

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<int> v1;      // "empty" int std::optional<int> 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.