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Re: Debugging and 'uninitialized value in concatenation' question
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From:
Tanton Gibbs
Date:
April 26, 2002 09:44
Subject:
Re: Debugging and 'uninitialized value in concatenation' question
Message ID:
007801c1ed41$47b0a2a0$0ea74ed8@brooklyn
If all you are doing is debugging the entrance to and exit of functions you
can look at aspect oriented programming. Search CPAN for Aspect. It may
allow you to do other things, but I know it will do that. Basically, you
can write functions that are called when other functions are called without
changing the other functions. Then, for debug mode, you can require the
aspect module you write and if not in debug, don't.
----- Original Message -----
From: "Jason Frisvold" <Jason.Frisvold@corp.ptd.net>
To: "Chas Owens" <cowens@intercall.com>
Cc: <beginners@perl.org>
Sent: Friday, April 26, 2002 11:44 AM
Subject: RE: Debugging and 'uninitialized value in concatenation' question
> While this appears to be a decent solution, I think I would still
> encounter the same problem that I wanted to avoid... Every time it
> encounters a CPP statement (#IF DEBUG, #DEFINE, etc) then it still needs
> to make the proper calls and whatnot... Whereas in C, since it's
> compiled, the pre-processor strips out the debug junk where appropriate
> as per your defines...
>
> I don't think the solution I want exists since this is not a compiled
> language... Other than writing a pre-processor style program that
> manually strips out the debug stuff I don't want...
>
> Hrm.. I wonder if I can make a module for CVS that will do this..
>
> ---------------------------
> Jason H. Frisvold
> Senior ATM Engineer
> Engineering Dept.
> Penteledata
> CCNA Certified - CSCO10151622
> friz@corp.ptd.net
> ---------------------------
> "Imagination is more important than knowledge. Knowledge is limited.
> Imagination encircles the world." -- Albert Einstein [1879-1955]
>
>
> -----Original Message-----
> From: Chas Owens [mailto:cowens@intercall.com]
> Sent: Friday, April 26, 2002 10:46 AM
> To: Jason Frisvold
> Cc: beginners@perl.org
> Subject: Re: Debugging and 'uninitialized value in concatenation'
> question
>
> On Thu, 2002-04-25 at 14:49, Jason Frisvold wrote:
> > Judging from the subject lines coming across the list today, I think
> I'm
> > gonna toss this question out there and then duck and cover... :-)
> >
> > I have 2 actual questions. I'll try to be as specific as possible..
> > :-)
> >
> > Question #1.
> >
> > When I'm writing code, I want to be able to view as much output as
> > possible so I can trace through everything and ensure that it is,
> > indeed, running correctly. I've gone as far as writing my own debug
> > module that uses "levels" and outputs everything in color.
> > (Term::ANSIColor is a lot of fun to play with)... One major side
> effect
> > of this is that my code will begin to run slower due to all of the
> > debugging...
> >
> > So, the obvious answer is to turn off the debugging. However, even
> with
> > my magic "debug off switch" (see below for a better explanation), the
> > calls to the debug routines are still being made. Is there any sort
> of
> > #IFDEF that can be done in perl, or do I actually have to comment out
> > (or remove) each call?
> >
> > My magic "debug off switch" is nothing more than a simple if/then
> > statement. It works on the principle that if $IDebugLevel is a
> positive
> > integer greater than 0, then I want to debug.
> >
>
> You can use cpp (the c preprocessor) with a filter like this:
>
> #!/usr/bin/perl -w
>
> use strict;
> use Filter::cpp; #from the Filter module on CPAN
>
> #DEFINE DEBUG 1
>
> print "this is normal code\n";
>
> #IF DEBUG
> print "this is debug code that simply goes away
> when DEBUG is set to 0.\n"
> #END IF
>
> If you are on a system that doesn't have cpp (almost all Unix boxen
> have cpp in one form or another) you can still roll your own filter
> similar to this:
>
> <example>
> package DEBUG;
>
> use Filter::Util::Call;
> use Carp;
>
> sub unimport {
> my ($type, @other_args) = @_;
> my $in_debug = 0;
>
> filter_add (sub {
> $l++;
>
> my $status = filter_read;
> croak "unbalenced '#DEBUG'" if $status == 0 and
> $in_debug;
>
> if (/^\s*#DEBUG ON/) {
> carp "nested #DEBUG ON is dangerous" if
> ++$in_debug > 1;
> } elsif (/^\s*#DEBUG OFF/) {
> croak "unbalenced '#DEBUG'" if --$in_debug < 0;
> } else {
> s/^/#/ if ($in_debug);
> }
>
> return $status;
> });
> }
>
> sub import {
> filter_del();
> }
>
> 1;
> </example>
>
> This module will allow you to say things like:
>
> <example>
> #!/usr/bin/perl
>
> use lib '.';
>
> no DEBUG; #turn off debugging code
>
> my $test = 0;
>
> #DEBUG ON
> print "This should not be printed if no DEBUG is used\n";
> #DEBUG OFF
>
> print "this should always print\n";
>
> use DEBUG; #turn debug code back on
>
> #this code should execute
> #DEBUG ON
> print "this should only show up if no DEBUG is not in effect\n";
> $test = 10;
> #DEBUG OFF
>
> no DEBUG; #turn debug back off
>
> #DEBUG ON
> print "This shouldn't be printed because of the no DEBUG above\n";
> #DEBUG OFF
>
> print "this \$test = ($test)\n"
> </example>
>
> > Question #2.
> >
> > Relating to the debugging, there are several instances where I have
> > variables that are only defined based on the definition of other
> > variables that exist elsewhere. Kind of like :
> >
> > sub dummy {
> > if ($a == 10) { my $b = 0; }
> > }
> >
> > $b is a local variable, so whenever the subroutine is exited, $b
> > vanishes into the ether. The problem is that I have $b in several
> debug
> > statements because I want to see it when it's used, but I don't want
> to
> > have to create a huge if/then structure to determine what variables
> are
> > being used.
> >
> > So, the general question becomes, how should variables like this be
> > handled? Should I be initializing them every iteration even if they
> go
> > unused, or should I be using some sort of defined() statement? What
> is
> > the "proper" way to handle this in perl? If this was C, I would have
> to
> > say that the variables are declared each time... I'm just curious if
> > there's a better way to handle this in perl...
> >
> >
> > TIA,
> >
> >
> > ---------------------------
> > Jason H. Frisvold
> > Senior ATM Engineer
> > Engineering Dept.
> > Penteledata
> > CCNA Certified - CSCO10151622
> > friz@corp.ptd.net
> > ---------------------------
> > "I love deadlines. I especially like the whooshing sound they make as
> > they go flying by." -- Douglas Adams [1952-2001]
> >
> >
> --
> Today is Sweetmorn the 43rd day of Discord in the YOLD 3168
> You are what you see.
>
> Missile Address: 33:48:3.521N 84:23:34.786W
>
>
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