From: travis@cs.columbia.edu (Travis Lee Winfrey)
Newsgroups: comp.lang.c,comp.unix.wizards,alt.sources,comp.sources.d,misc.misc
Subject: Re: #define DEBUG... (using printf for debugging)
Message-ID: <1990May4.161910.1353@cs.columbia.edu>
Date: 4 May 90 16:19:10 GMT

In article <40628@cornell.UUCP>, 
>gordon@mimir.cs.cornell.edu (Jeffrey  Adam Gordon) writes:
>
>    I want to have a DEBUG flag which controls whether diagnostic printfs
>    are executed or not.

Well, another variation on the debug macro with two parentheses
is to have a first argument that specifies the current level of
interest.  This argument can be compared with whatever you need: a
module-specific #define, a module-specific variable, a global
variable.  The two biggest problems with this method are the complaints
from lint about constants appearing in an if-statement, and that some
compilers may not strip out the code when you don't want the output.

A sample follow.  Note that the numbers here range from 1 to 4 because
I define DEBUG on a per-module basis.  Some other people specify their
interest in debugging information in terms of percentages, i.e., show
me 50% of everything you have in this module.  that's not intuitive
for me.

(I'm sorry if anyone else has already described this particular
fillip; I looked through all the messages posted so far, as many of
the previous posters should have done.)

/* 
 * debugging macros.  the dprintf macro takes two arguments, a
 * debugging level (1, 2, 3, 4) and a list of ordinary printf
 * arguments in parentheses, e.g.,
 *	dprintf(1, ("proc_kill_module: sys_ptr is NULL!\n"));
 * 
 * debugging levels:
 *     level 1: ordinary unexpected events which the programmer may want
 *              to know, but a user will not.  all "oh no!" type
 * 		information should be marked with this.
 *     level 2: more detailed, usually per-module information that
 * 		will a programmer will not want to know *unless* he or
 * 		she is debugging that module.
 *     Level 3: more detailed than 2, usually per-procedure
 * 		debugging information.  debugging statements this
 * 		low-level will be removed once gross errors are
 * 		found and removed.
 *     Level 4: just a level for demarcating extremely low-level,
 * 		usually inner-loop information.  removed as level 3 messages.
 *              
 */
# ifdef DEBUG
#       define dprintf(dlevel,printfargs)  if (dlevel <= DEBUG ) \
						printf printfargs  
# else /* DEBUG */
#	define dprintf(a,b)
# endif /* DEBUG */
--

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