CODEWITHSUNDEEP
c++c
user7090116
user7090116

Reputation:

Are 'null' and 'NULL' the same?

Are both null and NULL constants the exact same thing in C/C++?

I've noticed as I write my code in Visual Studio that null and NULL don't get the same syntax highlighting, and the compile outcome is not the same as having null instead of NULL in some sections of the code.

Upvotes: 2

Views: 1875

Answers (3)

Jean-Baptiste Yunès
Jean-Baptiste Yunès

Reputation: 36401

C standard says :

6.3.2.3/3 Pointers

An integer constant expression with the value 0, or such expression cast to type void *, is called a null pointer constant.

stddef.h then contains the NULL-define to that value.

C++ (another language, roughly related to C, certainly not in the way people usually think) used NULL in its very early versions (don't use it!). But in pre-C++11 releases, the constant 0 was defined as the way to represent pointers to nothing. Alas, this has some serious drawbacks and then C++11 defined the nullptr constant. Note that nullptr is a keyword.

C++ standard says:

2.14.17/1 Pointer literals

The pointer literal is the keyword nullptr. It is a prvalue of type std::nullptr_t. [ Note: std::nullptr_t is a distinct type that is neither a pointer type nor a pointer to member type; rather, a prvalue of this type is a null pointer constant and can be converted to a null pointer value or null member pointer value.]

3.9.1/10 Fundamental types

A value of type std::nullptr_t is a null pointer constant. Such values participate in the pointer and the pointer to member conversions. sizeof(std::nullptr_t) shall be equal to sizeof(void*).

About NULL in C++ standard says:

18.2/3 Types

The macro NULL is an implementation-defined C++ null pointer constant.

Upvotes: 2

varungupta
varungupta

Reputation: 154

C language has a NULL but there is no null. NULL is used to indicate the macro defined in and when discussing pointers.

use null when discussing the null character. null character refers to '\0'.

With that semantics out of the way, if you are asking for the difference between (x == '\0') and (x == NULL) it would depend on what x is. Use (x == '\0') if x is a char or int and (x == NULL) if x is a pointer.
For everything else you'd have to consider whether the comparison is valid and how things will be converted or promoted.

Upvotes: 0

Bathsheba
Bathsheba

Reputation: 234715

They might be, they might not be.

Both C and C++ define NULL, but in slightly different ways.

null is not part of either standard; it is neither a keyword nor a reserved word, so you can use it as a variable name, class name &c..

The preferred way of denoting pointer null-ness in C++ is nullptr which has type especially designed for pointer nullness.

Upvotes: 15

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