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From: SOFPJF@VM.UOGUELPH.CA (Peter Jaspers-Fayer)
Newsgroups: comp.sys.sgi
Subject: Mixed mode Arithmatic
Message-ID: <9102211136.aa10474@VGR.BRL.MIL>
Date: 21 Feb 91 15:44:18 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: Computing Services, University of Guelph, Ont. Can. N1G 2W1
Lines: 51

Seems that SGI C is different from any other C that we've seen when it
comes to adding pointers and long ints in various combinations.

#include <stdio.h>
main(){
long a, b, *P;
char s[2000];
 a = 2;
 b = 5;
 P = (long*)s;
 printf("Sizes: a P %d %d\n",sizeof(a),sizeof(P));
 printf("s,P:       %ld %ld\n", s,P);
 printf("a,b:       %ld %ld\n", a,b);
 printf("a+P+b:     %ld\n", a+P+b);
 printf("a+b+P:     %ld\n", a+b+P);
 printf("a+(P+b):   %ld\n", a+(P+b));
 printf("a+(b+P):   %ld\n", a+(b+P)); /* Watch this one */

}

Sequent and others:
Sizes: a P      4 4
s,P:            1073735252 1073735252
a,b:            2 5
a+P+b:          1073735280
a+b+P:          1073735280
a+(P+b):        1073735280
a+(b+P):        1073735280

SGI PI:
Sizes: a P      4 4
s,P:            2147467180 2147467180
a,b:            2 5
a+P+b:          2147467208
a+b+P:          2147467208
a+(P+b):        2147467208
a+(b+P):        2147467292   [!]


    As there does not appear to be a fixed standard, I can't say who's
"right", but this note will (I hope) serve as a warning to others that
may be surprised at how litterally SGI's C takes these sort of
expressions.

In every other compiler, I would guess that the ints are added together
first, then the result used to bump the pointer, regardless of the order
or punctuation of the expression.

 /PJ                                                SofPJF@VM.UoGuelph.Ca
         --------------------------------------
An ounce of application is worth a ton of abstraction.


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