Modifying Global Variable

Willman023 has asked for the wisdom of the Perl Monks concerning the following question:

Dear Fellow Monks,

I'm having quite a problem, using a function to alter a global variable. I'm hoping you guys can show me how to use a function to modify multiple variables. I'm trying to convert (YYYY-MM-DD HH:MM:SS) to unix time(seconds starting from 1970). I'm thinking about using Time::Local for the conversion. The error I'm getting before even trying to convert is:

Can't modify constant item in scalar assignment at calendar.pl line 276, near ""$year.$month.$day";"
Execution of calendar.pl aborted due to compilation errors.

Code:

my $date;
dateconverter($date_begin);
print $date, "\n";

sub dateconverter {
    my $year, my $month, my $day, my $hour, my $min, my $sec;
    ($year, $month, $day) = split /-/, $_;
    ($day, $hour) = split / /, $day;
    ($hour, $min, $sec) = split /:/, $hour;
    main::date = "$year.$month.$day";
    # get unix seconds for $date
        return main::date;
}
[download]

I originally tryed just setting the date by using $date = "$year..."; but read one of Ovid's nodes on scope and tried main::date with no luck. Thanks alot in advance for any advice!

Perl - the breakfast of Champions!

Comment on Modifying Global Variable Download Code

Replies are listed 'Best First'.
(z) Re: Modifying Global Variable by zigdon (Deacon) on Jan 08, 2003 at 17:38 UTC
There's a few problems with your code: Instead of "main::date" try "$date" - you shouldn't need to specify main:: unless you specified a different package. You are returning a value (the literal string "main::date"), but thankfully, you're not using it. You are splitting on an uninitialised variable ($_), which you would have known if you had warnings turned on. Use `$_[0]` instead. You can change all the splits into one split: `my ($year, $month, $day, $hour, $min, $sec) = split /[- :]/, $_[0];` [download] You don't need to modify the global - just return the value you need: `my $date = dateconverter($date_begin); print $date, "\n"; sub dateconverter { my @bits = split /[- :]/, $_[0]; return join ".", @bits[0,1,2]; }` [download] -- Dan	[reply] [d/l] [select]
Re: Modifying Global Variable by gryphon (Abbot) on Jan 08, 2003 at 18:02 UTC
Greetings Willman023 If you want to just convert from your YYYY-MM-DD HH:MM:SS format into UNIX time, then why not just use CPAN's Date::Parse? `use Date::Parse; print str2time('2003-01-08 09:55:36'), "\n";` [download] Or if you want to just save the datetime into $date: `use Date::Parse; my $date = str2time('2003-01-08 09:55:36');` [download] gryphon code('Perl') \|\| die;	[reply] [d/l] [select]
Re: Modifying Global Variable by boo_radley (Parson) on Jan 08, 2003 at 18:53 UTC
`Can't modify constant item in scalar assignment at calendar.pl line 276, near ""$year.$month.$day";"` This error is caused because you've forgotten the glyph to `main::date` -- it should be `$main::date`. Without the dollar sign, it's not considered a variable. You should be wary of using a global variable for a return value, too. Are you really sure you want to change $main::date every time you want convert to epoch time? This sort of side effect, as well as the logic behind omitting a local declaration, should be documented to whatever standards you have.	[reply]
Re: Modifying Global Variable by vek (Prior) on Jan 08, 2003 at 17:41 UTC
I think you're a little confused on how to return data from subroutines. I think this is what you want: `my $date = dateconverter($date_begin); print $date, "\n"; sub dateconverter { my $dateFoo = shift; # do stuff here, # store your end result in $somevar return $somevar; # returns the value }` [download] Your `$date` var will now contain the value of `$somevar`. -- vek --	[reply] [d/l] [select]


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