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From: lopez@uiucdcsp.cs.uiuc.edu
Newsgroups: comp.lang.c
Subject: Re: To comment 48: Xenix
Message-ID: <77200008@uiucdcsp>
Date: Wed, 29-Apr-87 14:25:00 EDT
Article-I.D.: uiucdcsp.77200008
Posted: Wed Apr 29 14:25:00 1987
Date-Received: Sat, 2-May-87 10:38:26 EDT
References: <77200001@uiucdcsp>
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Nf-ID: #R:uiucdcsp:77200001:uiucdcsp:77200008:000:2059
Nf-From: uiucdcsp.cs.uiuc.edu!lopez    Apr 29 13:25:00 1987



>/* Written  1:45 pm  Apr 27, 1987 by guy%gorodish@Sun.COM in uiucdcsp:comp.lang.c */
>you have some justification for flaming the author(s) of your
>compiler.  The two constructs are equivalent, and any good compiler
>will produce equally efficient code for them.

The above is irrelevant since I believed that
the null-pointer was equivalent to (int)zero. "apparently not true"
Plus I assumed a "dumb" compiler "in this day and age is very common."

>
>	1) a 32-bit zero value *is* an integer; it just doesn't
>	happen to be an "int";

True, but irrelevant:
(integer was used in terms of the latter, that doesn't need explanation).

>
>	2) "we" don't need a 32-bit zero value, we need a null
>	pointer of the appropriate type, and null pointers are not
>	integers.

paraphase: (null pointers internally are not integers)

When you enter (charptr == 0) in your "C" source code,
when the compiler takes its first pass and sees the zero, it will first
identify it as a zero and then see that it is a special case and make
the transformation.  If I am wrong, tell me.

for,

page  97 "K&R" 
"In general, integers cannot meaningfully be assigned to pointers;
zero is a special case."
::Quote.

By definition zero is an integer.
::Math.

Good argument for not having NULL being "0".
::Common Sense.

If NULL is not (int)zero, then C should not be using the symbol "0"
to represent it and (int)0.
::Statement.
:-> but by page 97 it appears that NULL is (int)zero and that it 
:-> is up to the compiler to take care of the special case.

Lastly,
   p. 192 says:

      "the assignment of the constant 0 to a pointer will produce a 
       null pointer".

       Meaning? the pointer now has the value of zero.
       (or can this be seen as compiler dependent).

       Can each compiler writer have their own way of representing 
       a NULL pointer (internally).

       We have two different types (pointers and integers)
       I seemed to have forgotten that; been writing too many
       lines of "C" lately.
>
>/* End of text from uiucdcsp:comp.lang.c */