On Mon, Jun 7, 2010 at 01:22, Bryan Harris <[email protected]> wrote:
snip
> How do other people deal with this? If I have a printf with seven complex
> (?, like the above) variables in it and one of them is undef, aside from
> breaking them all onto different print lines and re-running the script, how
> else can I figure out which one is undef?
snip
Finding the undef in print statements is easy: just look at the
output. I generally know what I expect to be in a given variable and
if it doesn't show up in the output, then that is the culprit. For
instance, if
print join(",", @list), "\n";
produces "foo,bar,,quux\n" then I know that the third element of @list
is undef. If
print "Ran $x tests against program $name\n";
produces "Ran 5 tests against program\n"; then I know $name is undef.
It is harder to find the undef if code like
my $n = $x * $y * $z;
One solution is to test in a debugger, but, I am ashamed to say, I
hate debuggers. They get in the way of how I do things. In general,
I drop in a warn or print statement like this:
print defined $x, defined $y, defined $z;
my $n = $x * $y * $z;
and rerun the code. But recently I have started using [Carp::REPL][1]
to test code. Here is an example session:
cow...@amans:~$ perl -MCarp::REPL=warn g.pl
Use of uninitialized value $z in multiplication (*) at g.pl line 10.
Trace begun at g.pl line 10
re.pl(main):001:0> :l
File g.pl:
5:
6: my $x = 5;
7: my $y = 10;
8: my $z;
9:
*10: my $n = $x * $y * $z;
11:
12: print "n is $n\n";
re.pl(main):002:0> defined $x ? $x : "undef"
5
re.pl(main):003:0> defined $y ? $y : "undef"
10
re.pl(main):004:0> defined $z ? $z : "undef"
undef
re.pl(main):005:0> :q
n is 0
cow...@amans:~$
It has most of the advantages of a debugger without all of the pain.
Of course, it can't stop at an arbitrary point in your code like a
debugger can, but it will stop at any warning or die. Well, that is a
bit of a lie, you can drop Carp::REPL::repl into your code and get the
REPL without a warn or die, but that requires changing your code:
cow...@amans:~$ perl g.pl
Trace begun at g.pl line 12
re.pl(main):001:0> :l
File g.pl:
7:
8: my $x = 5;
9: my $y = 10;
10: my $z;
11:
*12: repl;
13: my $n = $x * $y * $z;
14:
15: print "$n\n";
re.pl(main):002:0> $x
5
re.pl(main):003:0> $y
10
re.pl(main):004:0> $z
re.pl(main):005:0> $z = 3
3
re.pl(main):006:0> :q
150
cow...@amans:~$
[1] : http://search.cpan.org/dist/Carp-REPL/lib/Carp/REPL.pm
--
Chas. Owens
wonkden.net
The most important skill a programmer can have is the ability to read.
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