CODEWITHSUNDEEP
cnull
Plouff
Plouff

Reputation: 3470

NULL defined as 0 by my compiler std lib: is it correct?

The standard library of my C compiler defines NULL this way:

#define NULL 0

I would expect:

#define NULL ((void *)0)

Could someone tell me which one is correct and why?

Thank you!

Upvotes: 1

Views: 270

Answers (2)

Joe
Joe

Reputation: 410

In C language, the two way you said are both correct, both of they can be convert to other pointer that point to whatever object(any type) automatically, but in C++ language, #define NULL ((void *)0) is wrong, because void* can't be convert to other pointer automatically just like C.

Upvotes: 4

Frankie_C
Frankie_C

Reputation: 4877

The last revisions of C standard, C99 and C11, equates the null quantity to zero or null pointer.
From ISO/IEC 9899:201x §6.3.2.3 Pointers, point 3:

An integer constant expression with the value 0, or such an expression cast to type void *, is called a null pointer constant. If a null pointer constant is converted to a pointer type, the resulting pointer, called a null pointer, is guaranteed to compare unequal to a pointer to any object or function.

So what you see is a perfectly compliant NULL declaration of a C99-C11 compiler as opposed to the previous #define NULL ((void *)0) of pre C99 compilers.

Upvotes: 6

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