Path: utzoo!attcan!uunet!wuarchive!usc!apple!well!jef
From: jef@well.sf.ca.us (Jef Poskanzer)
Newsgroups: comp.lang.c++
Subject: Re: #defines....
Message-ID: <18899@well.sf.ca.us>
Date: 8 Jul 90 04:41:11 GMT
References: <33133@ut-emx.UUCP>
Reply-To: Jef Poskanzer <jef@well.sf.ca.us>
Organization: Paratheo-Anametamystikhood Of Eris Esoteric, Ada Lovelace Cabal
Lines: 30

In the referenced message, petrilli@walt.cc.utexas.edu (Chris Petrilli) wrote:
}The only time where you HAVE to use a #define (or at least, it is the best
}way for clarity) is in conditionally compiled code.  For example:
}
}#define DEBUG
}
}#ifdef DEBUG
} ... (do something) ...
}#endif

In many systems, the optimizers are smart enough to completely eliminate
code under a compile-time false if statement.  As in:

    const int debug = 0;

    if ( debug ) {
	(do something)
    }

Or whatever.  I have not checked whether this works in any C++ system,
but I have used it in numerous other systems, after checking the generated
machine instructions to be sure there was no run-time overhead.  One big
advantage of this over using the pre-processor is that the debugging code
gets syntax-checked, so you avoid bit rot.  One big disadvantage is that
it doesn't work on all systems, so it can't be considered portable.
---
Jef

  Jef Poskanzer  jef@well.sf.ca.us  {ucbvax, apple, hplabs}!well!jef
      A child of 5 could understand this!  Fetch me a child of 5.