Re: [boost] [uuid] Interface

Subject: Re: [boost] [uuid] Interface
From: Michael Marcin (mike.marcin_at_[hidden])
Date: 2008-12-29 14:49:36

Vladimir Batov wrote:
>>> the same -- 'm_uuid' initialized invalid -- but explicit about what 
>>> it actually does.
>>
>> I realize invalid vs nil/null was discussed earlier but I still don't 
>> like using those terms interchangeably.
> 
> I've been wondering where that "invalidity" property of nil/null comes 
> from for me? For me it certainly started with K&R stating "The symbolic 
> constant NULL is ... to indicate more clearly that this is a special 
> value for a pointer." That is, it was not just another but special 
> pointer to start with. Then, through many years, that "special" property 
> has been firmly ingrained for me as "invalid" due to
> 
> char* p1;
> char* p2 = NULL;
> char* p3 = "mama";
> 
> strlen(p1); // bombs
> strlen(p2); // bombs
> strlen(p3); // good
> 
> For all practical purposes the above makes p1 and p2 quite 
> naughty/bad/invalid compared to the well-behaving p3. Despite NULL's 
> quite official status in the language(s), strlen() clearly "thinks" that 
> NULL is anything but valid and bombs spectacularly. Then, I habitually 
> extended that notion onto any foo::null() and ultimately to uuid::nil().
> 
> 

Sorry for the late response. I disagree that NULL is invalid. Reading or 
comparing against the value of a NULL pointer is valid but not so 
against an uninitialized pointer. There are functions other than strlen 
where NULL does not bomb but has a well defined meaning and purpose, 
like strtok.

FWIW uninitialized seems to be considered singular by the standard

24.1/5

[Example:
After the declaration of an uninitialized pointer x (as with int* x;), x 
must always be assumed to have a
singular value of a pointer.  ]

-- 
Michael Marcin