TeamSolCO wrote:
> To start, let me say this:
> 1) I have both "Learning Perl 3rd Ed" and "Programming Perl 3rd Ed"
> 2) I have read "Learning Perl 3rd Ed", and I use "Programming Perl 3rd Ed" as
> reference.
> 3) I have searched with Google for several key words related to my problem, but the
> mass of junk I get back is not
> helpful.
> 4) The application source is roughly 450 lines long, and the FAQ for this list asks
> users not to mass-post such things,
> otherwise I'd post it here en-masse for help.
>
> And, most importantly:
> A) I didn't write the application I'm working on, I extended it (to a great deal)
> using the same programming style as
> the original author (and other programmers before me), except that I've been
> "cleaning up" the old code a great deal.
> B) I understand this application is quite old, probably written in Perl 4 days, and
> shows no OO influence (was
> originally written as a down-and-dirty utility script).
>
> That said, please do not assume that I am incompetent; I'm just frustrated. I've
> been programming for more than 20
> years, just not with Perl (no, I'm not a VB "programmer" -- my experience is
> primarilly C).
>
> Now then, I've opened a can of worms by adding "use strict" and "use warnings" to
> the source. Keep in mind that this
> application was running JUST FINE before doing this. I'm only trying to 'modernize'
> this old code. Having started with
> a couple screen-fulls of resulting errors, I'm down to just one: "Can't use an
> undefined value as a symbol
> reference..." The partucular block that causes this error is:
>
> sub close_fifo {
> close($hndFIFO);
Why is an old C programmer doing this? It is very clear that the function above makes
use of some variable $hndFIFO. Where
does this variable come from? How is it scoped and where is it initialized? You know
that these things should not be left
a mystery. Although Perl does not require formal function signatures, good structre
still calls for explicit passing of
arguments, and explicit declarations of identifiers being used.
The interpreter is asking where this value gets its definition. You should give it an
answer.
> }
>
> It's related open sub is:
>
> sub open_fifo {
> close_fifo();
Don't count on this filehandle being global. Most likely, in the course of cleaning
up other portions of the code, you
inadvertently declared the filehandle within some lexical scope. Don't try to reverse
that action, as it represent
progress. Instead, trace the filehandle toits opening make sure it is declared within
an appropraite scope, and then
explicitly store, and pass it so that it is available, properly defined, when needed.
> # Make sure the $hndFIFO file is a pipe.
> unless (-p $path_fifo) {
> unlink($path_fifo);
> system("mkfifo $path_fifo") or die("Can't mkfifo $path_fifo: $!");
> chmod(0600, $path_fifo);
> }
>
> # Open the $hndFIFO stream.
> open($hndFIFO, "< $path_fifo") or die("Can't open $path_fifo: $!");
> }
>
> and, at the top of this source, I have declared $hndFIFO (along with the log file
> handle) using our as in:
>
> our ($hndLOG, $hndFIFO);
Hard to say without looking at the source as a whole. Why not just call it
serindipity that this global declaration failed,
and try again using careful and well-though-out lexical scoping. If you have been
programming that long, you should know
that globals are poison seeds in code of any complexity.
>
>
> Before applying the aforementioned pragmas, the FIFO handle was simply, FIFO. There
> was no "our" declaration, at all,
> and the variable/handle name was not prefixed with the scalar $ indicator.
> Everything worked at that time... Clearly,
> I'm trying to delcare the FIFO (and log file) file handles as global to the
> application so that I can access them freely
> in several other subs. What do I need to do to satisfy the strict pragma, while
> accomplishing my goal?
>
> Thanks!!
>
> - William Kimball
> "Programming is an art-form that fights back!"
Well, william, you are on the right track. Do not regret integrated error-detection
in your code. Work with the messages
it gives. It was obvious to me, without seeing any error messages, that there was
something funky about an identifier
popping up out of thin air to be used in a function.
For what its worth, Perl is more tolerant on this issue than I am. You may well be
able to address this issue by specifying
your intent to use the more-broadly-scoped value. Perl allows the redeclaration of
our variables within a scope, and takes
this as a signal to use the variable declared in the outer scope:
sub close_fifo {
our$hndFIFO;
close($hndFIFO);
}
Whether that will be enough, I don't know. The error message reffered to a lack of
definition, not to improper declaration,
so you will have to trace through all code that addresses this global to see that it
is getting properly assigned, and that
no loose cannons are blowing it away before it gets used. That goes with the
territory when using globals.
Joseph
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