Just for the sake of thoroughness, there is another
problem with using macros instead of functions. Even
if you have everything properly parenthesized, what
happens to this:
int n, m;
n = -3;
m = Abs(n++);
If Abs() were a function, m would be 3 and n would be -2.
With the macro
> #define Abs(a) (((a) >= 0) ? (a) : -(a))
the statement expands to:
m = (((n++) >= 0) ? (n++) : -(n++));
Which would leave n at -1 when all is said & done.
The autoincrement & autodecrement operators are the bane
of all macro writers...
--
-Richard M. Hartman
[EMAIL PROTECTED]
186,000 mi./sec ... not just a good idea, it's the LAW!
> -----Original Message-----
> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]
> Sent: Wednesday, March 17, 1999 12:59 PM
> To: [EMAIL PROTECTED]
> Subject: Re: Abs() macro in sysutil.h is incorrect
>
>
>
> >Actually there should be parens around the first "a" too:
> > #define Abs(a) (((a) >= 0) ? (a) : -(a))
>
> Consider this now fixed.
>
> Until you get headers with this change, I suggest adding
>
> #undef Abs
> #define Abs(a) (((a) >= 0) ? (a) : -(a))
>
>
> >My rule of thumb is to always put parens around EVERY occurence of a
> >macro argument in the expansion.
>
> This is very good advice.
>
>
> Thanks for the report.
>
>
> -Roger Flores
>
>
>
