Is lowercase null valid in C++?

Question

Is there any lowercase null in any version of C++ language specification?

Background:

I was asked in an interview "Which of the following pointer initializations are valid?", and I filled the form something like:

// valid
    int* p1 = 0;
    int* p2 = 2-2;
    int* p6 = new int;
// invalid
    int* p3 = 1; 

    int z = 0;
    int* p4 = z;
// ???
    int* p5 = null;

Nothing stops you from making a `null` macro, just like how `NULL` is a macro. — Blaze, Jun 19 '19 at 06:33
@Top-Master int* p5 = null; can be valid or invalid depending on how null is defined.:) — Vlad from Moscow, Jun 19 '19 at 06:33
@blaze Hopefully an idea of engineering sanity would stop you from doing that. — lubgr, Jun 19 '19 at 06:34
@Top-Master And my advice: never do assignments in an interview. Interview is not an exam.:) — Vlad from Moscow, Jun 19 '19 at 06:35
I would avoid the lowercase `null` just from a readability standpoint. When someone is scanning your code the will either be looking for `NULL` or `nullptr`. `null` would just provide a double-head-turn or be skimmed over entirely. — David C. Rankin, Jun 19 '19 at 06:37
@StoryTeller Does C++ make it invalid? It's perfectly valid C. — melpomene, Jun 19 '19 at 06:38
@Raffallo `int z = 0; int* p4 = z;` is a single example. `z` is an `int`. — melpomene, Jun 19 '19 at 06:42
@melpomene - Very sneakily so, it does https://stackoverflow.com/questions/55780426/implementing-the-linux-kernels-is-constexpr-ice-p-macro-in-pure-c — StoryTeller - Unslander Monica, Jun 19 '19 at 06:42
@lubgr true that - in C++ even using `NULL` is questionable when there's `nullptr`. — Blaze, Jun 19 '19 at 06:50

score 22 · Accepted Answer · answered Jun 19 '19 at 06:36

22

Is there any lowercase null in any version of the C++ language specification?

No.

answered Jun 19 '19 at 06:36

Nikos C.

50,738
9
71
96

5

Well, yeah, that does it. – StoryTeller - Unslander Monica Jun 19 '19 at 06:44
1

It would be better with a reference-link or something, but still, this seems to be the right answer. – Top-Master Jun 19 '19 at 07:25
5

@Top-Master Yeah, this requires proving a negative. The evidence of absence here is the lack of any section in the C++ standard that mentions `null` as a valid token. So really, "no" is pretty much the perfect answer IMO. :-) – Nikos C. Jun 19 '19 at 07:31
1

@Top-Master The only guarantee you have is that advanced C++ programmers looked at this answer and agree due to the lack of comments :) – Rakete1111 Jun 21 '19 at 11:35

score 8 · Answer 2 · answered Jun 19 '19 at 06:45

A one word answer would be NO.

try the below code

  #include <iostream>
#include <stdlib.h>
using namespace std;
int main(){
    int *p = null;
    int *q = NULL;
    return 0;
}

This gives the below error on compilation:

error: ‘null’ was not declared in this scope

Which is self explanatory.

score 2 · Answer 3 · answered Jun 19 '19 at 07:05

The answer is written in some of the header files. NULL is the predefined macro in those header files such as **

-> #define NULL 0

**. Hence we can only define with uppercase "NULL" to avoid the compilation termination.

However, if you wish for lower case null, you can do so by defining the new macro or make charges in predefined macro in the header file. but be careful before you want to make these changes.

Is lowercase null valid in C++?

Background:

3 Answers3