l i n u x - u s e r s - g r o u p - o f - d a v i s
Next Meeting:
July 7: Social gathering
Next Installfest:
Latest News:
Jun. 14: June LUGOD meeting cancelled
Page last updated:
2007 Jan 19 14:34

The following is an archive of a post made to our 'vox-tech mailing list' by one of its subscribers.

Report this post as spam:

(Enter your email address)
Re: [vox-tech] Nifty macro expansion bug
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [vox-tech] Nifty macro expansion bug

On Thu 18 Jan 07,  4:14 PM, Bill Kendrick <nbs@sonic.net> said:
> So at work, a coworker noticed an issue with the following code:
>   for (i = 0; i < n; i++)
>     myFREE(foo[i]);
> which went away when he wrapped it in braces:
>   for (i = 0; i < n; i++)
>   {
>     myFREE(foo[i]);
>   }
> Figured maybe it was a weird compiler bug.  Being author of the myFREE()
> code -- which happens to be a macro -- I realized immediately what I did
> wrong.  (And continue to be annoyed with C syntax ;) )
> See, myFREE() is actually a macro that looks like this:
>   #define myFREE(x) if ((x) != NULL) FREE(x); x = NULL;
> Two statements... hence the need for {} around the call to the macro.
> (Or, more sensibly, including {}s around what the macro expands to.)
> That was a neat catch. :)

I ran into something similar, but more complicated, last week.  An
expression that should've executed didn't.

I looked at the output of "cl.exe -E" (similar to gcc -E) which displays
what the compiler "sees" after the preprocessor does its thing.  From this
view, it was easy to see that what looked like:

   if ( some condition )
      die( some error message )

was arriving at the compiler as:

   if ( some condition )
      if ( lots of stuff )
         print error message with lots of stuff.

So the code needs to look like:

   if ( some condition ) {
      die( some error message )
   } else {


How VBA rounds a number depends on the number's internal representation.
You cannot always predict how it will round when the rounding digit is 5.
If you want a rounding function that rounds according to predictable rules,
you should write your own.
              -- MSDN, on Microsoft VBA's "stochastic" rounding function

Peter Jay Salzman, email: p@dirac.org web: http://www.dirac.org/p    
PGP Fingerprint: B9F1 6CF3 47C4 7CD8 D33E  70A9 A3B9 1945 67EA 951D
vox-tech mailing list

LUGOD Group on LinkedIn
Sign up for LUGOD event announcements
Your email address:
LUGOD Group on Facebook
'Like' LUGOD on Facebook:

Hosting provided by:
Sunset Systems
Sunset Systems offers preconfigured Linux systems, remote system administration and custom software development.

LUGOD: Linux Users' Group of Davis
PO Box 2082, Davis, CA 95617
Contact Us

LUGOD is a 501(c)7 non-profit organization
based in Davis, California
and serving the Sacramento area.
"Linux" is a trademark of Linus Torvalds.

Sponsored in part by:
O'Reilly and Associates
For numerous book donations.