Unknown problem, throws "Useless use of privt var in void contxt"

S0ci1_Hak0n has asked for the wisdom of the Perl Monks concerning the following question:

I do know some perl, and this is a project i've been working on for some time. The compiler and komodo tell me there is a error on line 140, namely "Useless use of private variable in void context at #PATH#/main.pl line 140." It is a sub, called only once. I am running it in -w mode.

# Called as: my @ch_refnums = &findTickers($file_cont, $anndate);
sub findTickers {
    my ($file, $ann_date) = @_;
    
    my $match;
    my $max_month = 0;
    my $max_year = 0;

    @temp = split (/\//, $ann_date);
    my $month = $temp[0];
    my $day = $temp[1];
    my $year = $temp[2];

    if ($month => 10)  {
        $max_month = $month-9;
        $max_year = $year+1;
    }
    elsif ($month < 10) {
        $max_month = $month+3;
    }

==> if ($max_year > 1900)    {    # Error occurrs here.
    $match = "[$month-$max_month][\/][1-3]?[0-9][$year|$max_year]" ;
    }
    else    {
        $match = "[$month-$max_month][\/][1-3]?[0-9][$year]" ;
    }
}
[download]

There is more to the sub and prog. However, I think it is somewhere here that the error is actually occurring. This error does not appear to be fatal, but i would want to know why it occurs... Thanks! Jon

Comment on Unknown problem, throws "Useless use of privt var in void contxt" Download Code

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Re: Unknown problem, throws "Useless use of privt var in void contxt" by Joost (Canon) on Jan 21, 2008 at 22:41 UTC
Perl can give confusing line numbers in if ... else statements sometimes. When that happens, the error is usually a few lines ~~above~~ below the reported line. but it here it appears above, for some reason This: `if ($month => 10) {` [download] is wrong, and could be the cause, since it evaluates $month in void context. Did you mean `if ($month >= 10) {` instead? "What should it profit a man, if he should win a flame war, yet lose his cool?"	[reply] [d/l] [select]
Re^2: Unknown problem, throws "Useless use of privt var in void contxt" by S0ci1_Hak0n (Novice) on Jan 21, 2008 at 22:51 UTC
lol. Don't know how I missed that! Thanks	[reply]
Re: Unknown problem, throws "Useless use of privt var in void contxt" by bigmacbear (Monk) on Jan 21, 2008 at 22:43 UTC
I'd take a look at the line `if ($month => 10) {` which actually boils down to `if ("$month", 10) {` since "=>" is the "fat comma" operator, used in defining hashes, whose only distinction from the comma operator is that it ensures its left-hand argument is a string. I think you meant to say `if ($month >= 10) {` instead. Not sure why the error appears so far down, but there you are.	[reply] [d/l] [select]
Re^2: Unknown problem, throws "Useless use of privt var in void contxt" by halley (Prior) on Jan 22, 2008 at 14:13 UTC
Your explanation of `=>` is not entirely accurate. `if ($month => 10) { ... }` [download] is equivalent to `if ($month, 10) { ... }` [download] The `=>` operator does NOT wrap whatever appears on the left into a string. Instead, it allows any expression, but if a bareword is used, it turns the bareword into a string. Any other expression is left as-is, not even coerced into being a string. (Actually rolling a list into a hash will coerce the keys into strings unless the hash has some magic.) -- `[ e d @ h a l l e y . c c ]`	[reply] [d/l] [select]
Re: Unknown problem, throws "Useless use of privt var in void contxt" by Anonymous Monk on Jan 21, 2008 at 22:38 UTC
Not sure about the error, per say, but DO NOT DO THIS! `my @ch_refnums = &findTickers($file_cont, $anndate);` [download] Do this instead: `my @ch_refnums = findTickers($file_cont, $anndate);` [download] Only use & if you are overriding one of Perl's built-in functions.	[reply] [d/l] [select]
Re^2: Unknown problem, throws "Useless use of privt var in void contxt" by S0ci1_Hak0n (Novice) on Jan 21, 2008 at 22:50 UTC
Thx for that tip, i've been using an ancient tome to perl, and that's how it says to do it. One q, why would it be important to remove the &? thx Jon	[reply]
Re^3: Unknown problem, throws "Useless use of privt var in void contxt" by Joost (Canon) on Jan 21, 2008 at 22:56 UTC
See for example, Using & in function calls. "What should it profit a man, if he should win a flame war, yet lose his cool?"	[reply]
Re^4: Unknown problem, throws "Useless use of privt var in void contxt" by Erez (Priest) on Jan 22, 2008 at 09:25 UTC
Re^5: Unknown problem, throws "Useless use of privt var in void contxt" by Joost (Canon) on Jan 22, 2008 at 13:14 UTC
Re: Unknown problem, throws "Useless use of privt var in void contxt" by starX (Chaplain) on Jan 21, 2008 at 22:48 UTC
Where else is `$match` accessed? I would understand that warning to mean that you've saved data to a variable that goes out of scope before you try accessing or returning it. Are you forgetting to return `$match` at the end of this sub? I ask because I don't see you doing so explicitly. --starX, www.axisoftime.com	[reply] [d/l] [select]
Re^2: Unknown problem, throws "Useless use of privt var in void contxt" by S0ci1_Hak0n (Novice) on Jan 21, 2008 at 22:57 UTC
The problem was that backwards => (meant to be >=). Thanks anyway! I still can't believe I got 3 responses in 10 min, though... Jonathan	[reply]


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