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From: jsmoller@jsmami.UUCP (Jesper Steen Moller)
Newsgroups: comp.sys.amiga.programmer
Subject: Re:  Compiler code (was a flame fest) (now a lesser flame fest)
Message-ID: <jsmoller.4971@jsmami.UUCP>
Date: 26 Apr 91 07:15:22 GMT
Followup-To: comp.sys.amiga.programmer
Organization: Danish SofTech
Lines: 70

In article <dillon.6879@overload.Berkeley.CA.US> dillon@overload.Berkeley.CA.US (Matthew Dillon) writes:
> 
> In article <91112.093750GHGAQZ4@cc1.kuleuven.ac.be> GHGAQZ4@cc1.kuleuven.ac.be writes:
> >>  Nope.  ++ and -- are unary operators of the highest precedence.  The only
> >>difference between ++x and x++ is the value they assume, the order of eval-
> >>uation follows standard C precedence..
> >
> >I think you are wrong. Look at the following results :
> >I have tried this with our mainframe compiler :
> >   int n=4;
> >
> >   (n--)*(n++)   ->   12
> >   (n++)*(n--)   ->   20
> >   (--n)*(++n)   ->   16
> >   (++n)*(--n)   ->   16
> >   (--n)*(n++)   ->   12
> >   (++n)*(n--)   ->   20
> >   (n--)*(++n)   ->   16
> >   (n++)*(--n)   ->   16
> >
> >	   Jorrit Tyberghein
> 
>     Obviously the compiler is going to do it a certain way, but that
>     represents only the particular implementation of the compiler used. If
>     you have an expression:
> 
> 	exp1 * exp2
> 
>     There is NO GUARENTEE on the order of evaluation... exp1 before exp2 or
>     exp2 before exp1, no matter *what* exp1 and exp2 contains.	Period.

Aha! A friend of mine asked if you could rely on the following:
---- FICTIVE CODE START ----

int func1(void);
int func2(void);

int result;

    result=func1()+func2();
---- FICTIVE CODE END ----

Question: Can't you rely on func1() being called before func2()???
Really not?

> 	++a + ++a
> 
>     If a is 1, the result can be 2 + 2 or 2 + 3 or 3 + 2 and at the end 'a'
>     can be either 3 or 4 depending on how the compiler was designed. DO NOT
>     DEPEND ON ANY PARTICULAR SIDE EFFECT WITH ++ or -- ACTING ON THE SAME
>     VARIABLE MORE THAN ONCE IN ANY EXPRESSION, EVER, OR YOUR CODE WILL BE
>     UNPORTABLE EVEN ACROSS REVISIONS OF THE SAME COMPILER!

H*ll to debug, anyway... min() and max() rules!!!

Oh, by the way: func(a++)

Is "a" increased before or after the function call. I think I once read in
K&R that it was undefined, but I might be mistaken.


> 					    -Matt

Greets, Jesper

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