Mandeep Sandhu wrote:
On 10/24/06, *Momchil Velikov* <velco@xxxxxxxxx
<mailto:velco@xxxxxxxxx>> wrote:
Mandeep Sandhu wrote:
> Hi All,
>
> This is more of a 'C' question than a kernel one. But since i'll be
> putting this
> in a module, I thought I'd ask here too...
>
> Whats the correct way to initialize a pointer?
>
> 1. char *p = 0;
> OR
> 2. char *p = NULL;
"[#3] An integer constant expression with the value 0, or
such an expression cast to type void *, is called a null
pointer constant."
You could do char *p = 1 - 1; char *q = 0; char *r = 1 / 2;
if you wish.
Thats an interesting way of writing zero! :)
I read some time ago (can't remember where!), that 0 is not always
an invalid address.
Depends on what you call invalid address. There's no object pointed
to by a null pointer, thus you must not dereference it. This is
regardless of whether the environment would trap the null access or
would silently return whatever bytes are at address zero.
Though I think the C compiler is supposed to generate
one for any such assignments (as shown above).
C compiler is supposed to initialize the pointers wioth the null pointer
constant, regardless of the null pointer constants representation.
Is this a C standard?
Yes.
Are all compilers supposed to do it?
Only C compilers.
Shouldn't NULL be a better choice so that we can #define it to an invalid
value, where this #define is specific to an architechture?? CMIIW.
If you want don't like your pointers initialized with that specific
invalid value, called ``null pointer constant'', I suggest you #define,
say, INVALID_POINTER_VALUE and not overload the semantics of NULL.
~velco
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