CODEWITHSUNDEEP
c++null
JT.
JT.

Reputation: 945

C++ nil vs NULL

OK, I have some C++ code in a header that is declared like this:

void StreamOut(FxStream *stream,const FxChar *name = nil);

and I get: error: 

'nil' was not declared in this scope

nil is a pascal thing, correct?

Should I be using NULL?

I thought they were both the same or at least Zero, no?

Upvotes: 12

Views: 39527

Answers (7)

friendzis
friendzis

Reputation: 809

If you run a search through glibc you'll find this line of code:

#define NULL 0

It's just a standard way (not sure if it was published anywhere) of marking empty pointers. Variable value of 0 is still a value. Pointer pointing to 0 (0x0000... (it's decimal zero)) is actually pointing nowhere. It's just for readability.

int *var1, var2;
var1 = 0;
var2 = 0;

The above two assignments are not the same though they both look the same

Upvotes: 1

notnoop
notnoop

Reputation: 59307

Yes. It's NULL in C and C++, while it's nil in Objective-C.

Each language has its own identifier for no object. In C the standard library, NULL is a typedef of ((void *)0). In C++ the standard library, NULL is a typedef of 0 or 0L.

However IMHO, you should never use 0 in place of NULL, as it helps the readability of the code, just like having constant variables in your code: without using NULL, the value 0 is used for null pointers as well as base index value in loops as well as counts/sizes for empty lists, it makes it harder to know which one is which. Also, it's easier to grep for and such.

Upvotes: 6

Sean Copenhaver
Sean Copenhaver

Reputation: 10685

I saw some comments on why not to use 0. Generally people don't like magic numbers, or numbers with meaning behind them. Give them a name. I would rather see ANSWER_TO_THE_ULTIMATE_QUESTION over 42 in code.

As for nil, I know Obj-C using nil as well. I would hate to think that someone went against the very popular convention (or at least what I remember) of NULL, which I thought was in a standard library header somewhere. I haven't done C++ in awhile though.

Upvotes: 0

Jack
Jack

Reputation: 133609

just add at the beginning

#define null '\0'

or whatever you want instead of null and stick with what you prefer. The null concept in C++ is just related to a pointer pointing to nothing (0x0)..

Mind that every compiler may have its own definition of null, nil, NULL, whatever.. but in the end it is still 0.

Probably in the source you are looking at there is a 

#define nil '\0'

somewhere in a header file..

Upvotes: 0

JaredPar
JaredPar

Reputation: 755269

In C++ you need to use NULL, 0, or in some brand new compilers nullptr. The use of NULL vs. 0 can be a bit of a debate in some circles but IMHO, NULL is the more popular use over 0.

Upvotes: 19

Guido
Guido

Reputation: 37

0 is the recommended and common style for C++

Upvotes: 1

Marcin
Marcin

Reputation: 12620

nil does not exist in standard C++. Use NULL instead.

Upvotes: 14

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