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

In the program listed below I have two global variables that don't work like I want. @ContactIDList is a list of ID numbers that is collected in a subroutine. I can print out the list in the subroutine, but not in the if statement from which I call the subroutine. $CurIDPtr is supposed to keep track of which ID is being used currently, but in the outer if statement it's value is always 0. I assumed this was a scoping problem and changed the declarations to use 'our' but that hasn't helped. Appreciate any help on this. Here is my code: 
#!/usr/bin/perl -w
# Russell Hyland
# WebHortLine SearchContacts.cgi
#
# Prompt for search string, then get a list of ContactIDs of Contact r
+ecords that contain the searchstring in
# one or more fields. Use the list to display the records.

use strict;
use warnings;
use CGI::Carp qw();
use CGI::Pretty;
use CGI qw(:standard :cgi-lib -debug fatalsToBrowser);
use DBD::mysql;
use DBI;
    
my $cgi = new CGI;
my @css = (Link({-rel=>'stylesheet',-type=>'text/css',-src=>'Styles.cs
+s',-media=>'screen'}));

my ($dbh, $selectstr, $sth, @row);
my $SrchStr;
our @ContactIDList;
our $CurIDPtr = 0;

my $County = $cgi->cookie('MG_HortLine');
if (!$County) {
    print redirect(-location=>"http://hortline.rbhyland.org/Login.cgi"
+);
} 

print $cgi->header();

print start_html(-title =>'Search Contacts',
                 -style =>'Styles.css',
                 -script=>{-language=>'JAVASCRIPT',
                 -src=>'Scripts.js'});
print "<img src='http://www.hortline.rbhyland.org/MGLogo.jpg' alt='MG 
+logo' align='left' />";
print "<h1>&nbsp;Penn State Consumer<br /><br />&nbsp;Horticultural He
+lp Line</h1><br />";
print h2('Search Contacts'),hr;


if (!param('SearchFld') && !param('Next') && !param('Prev')) {
    print start_form,
          "<label for='SearchFld'>Search </label>",
          textfield(-name=>'SearchFld',-value=>"",-size=>30,-maxlength
+=>50,-id=>'SearchFld', -class=>'DataIn'),
          br,br,submit,
          end_form;
} elsif (param('Next')) {
    $CurIDPtr += 1;
    print '[',$CurIDPtr,'][',$ContactIDList[$CurIDPtr],']';
    DisplayRec();
} elsif (param('Prev')) {
    $CurIDPtr = $CurIDPtr - 1;
    print Dump;
    print '[',$CurIDPtr,'][',$ContactIDList[$CurIDPtr],']';
    DisplayRec();
} else {
    getIDs();
    DisplayRec();
}

print end_html;

[download]
sub DisplayRec {

    $dbh = DBI->connect("DBI:mysql:database=hortline;host=mysql.hortli
+ne.rbhyland.org","rbhyland","dh_R95w")
                        or &dienice("Database logon failed: $DBI::errs
+tr\n");
    $selectstr = "SELECT * ".
                    "FROM Contacts ".
                    "WHERE ContactID = ?; ";
    $sth = $dbh->prepare("$selectstr");
    $sth->execute("$main::ContactIDList[$main::CurIDPtr]") or &dbdie;
    
    @row = $sth->fetchrow_array();
    &dienice("Data fetching error: $DBI::errstr\n") if $DBI::err;
    
my    $FirstName                    = $row[2];
my    $LastName                    = $row[3];
my    $Address                    = $row[4];
my    $City                        = $row[5];
my    $State                        = $row[6];
my    $Zip                        = $row[7];
my    $Muni                        = $row[8];
my    $ClientType                    = $row[9];
my    $Phone                        = $row[10];
my    $EmailName                    = $row[11];
my    $ContactMethodPhone            = $row[12];
my    $ContactMethodWalkIn        = $row[13];
my    $ContactMethodEmail            = $row[14];
my    $ContactMethodEvent            = $row[15];
my    $Answer                        = $row[16];
my    $Question                    = $row[17];
my    $MasterGardener                = $row[18];
my    $CallDate                    = $row[19];
my    $InfoProvidedVerbally        = $row[20];
my    $InfoProvidedFaxed             = $row[21];
my    $InfoProvidedMailed            = $row[22];
my    $InfoProvidedHandout        = $row[23];
my    $InfoProvidedWebsite        = $row[24];
my    $SampleStatusDue            = $row[25];
my    $SampleStatusReceived        = $row[26];
my    $SampleStatusSentToPSU        = $row[27];
my    $CallCompleteDate            = $row[28];
my    $CallBackDate                = $row[29];
my    $MGCallBack                    = $row[30];
my    $FactSheets                 = $row[31];
my    $Topic                        = $row[32];

    print    "<label for='FirstNameFld'>Name</label>",
            textfield(-name=>'FirstNameFld',-value=>$FirstName,-size=>
+50,-maxlength=>50,
                        -id=>'FirstNameFld', -readonly=>'readonly', -c
+lass=>'DataIn'),
#            br,
#            "<label for='LastNameFld'>Last Name</label>",
            textfield(-name=>'LastNameFld',-value=>$LastName,
                    -size=>50,-maxlength=>50,-id=>'LastNameFld', -read
+only=>'readonly', -class=>'DataIn2'), 
            br,
            "<label for='AddressFld'>Address</label>",
            textfield(-name=>'AddressFld',-value=>$Address,
                    -size=>50,-maxlength=>50,-id=>'AddressFld', -reado
+nly=>'readonly', -class=>'DataIn'),
#            br,
#            "<label for='CityFld'>City</label>",
            textfield(-name=>'CityFld',-value=>$City,
                    -size=>50,-maxlength=>50,-id=>'CityFld', -readonly
+=>'readonly', -class=>'DataIn2'),
#            br,
#            "<label for='StateFld'>State</label>",
            textfield(-name=>'StateFld',-value=>$State,
                    -size=>2,-maxlength=>2,-id=>'StateFld', -readonly=
+>'readonly', -class=>'DataIn3'),
#            br,
#            "<label for='ZipFld'>Zip</label>",
            textfield(-name=>'ZipFld',-value=>$Zip,
                    -size=>10,-maxlength=>10,-id=>'ZipFld', -readonly=
+>'readonly', -class=>'DataIn4'),
            br,
            "<label for='MuniFld'>Municipality</label>",
            textfield(-name=>'MuniFld',-value=>$Muni,
                    -size=>50,-maxlength=>50,-id=>'MuniFld', -readonly
+=>'readonly', -class=>'DataIn'),
            br,
            "<label for='EmailFld'>Email</label>",
            textfield(-name=>'EmailFld',-value=>$EmailName,
                    -size=>50,-maxlength=>50,-id=>'EmailFld', -readonl
+y=>'readonly', -class=>'DataIn'),
            br,
            "<label for='PhoneFld'>Phone</label>",
            textfield(-name=>'PhoneFld',-value=>$Phone,
                    -size=>20,-maxlength=>20,-id=>'PhoneFld', -readonl
+y=>'readonly', -class=>'DataIn'),
            br,
            "<label for='ClientTypeFld'>Client Type</label>",
            textfield(-name=>'ClientTypeFld',-value=>$ClientType,
                    -size=>20,-maxlength=>20,-id=>'ClientTypeFld', -re
+adonly=>'readonly', -class=>'DataIn'),
            br,
            "<label for='CallDateFld'>Call Date </label>",
              textfield(-name=>'CallDateFld',-value=>$CallDate,-size=>
+10,-maxlength=>10,-id=>'CallDateFld',
              -class=>'DataIn', -readonly=>'readonly'),
            br,
            "<label for='CallBackDateFld'>Call Back </label>",
              textfield(-name=>'CallBackDateFld',-value=>$CallBackDate
+,-size=>10,-maxlength=>10,
                          -id=>'CallBackDateFld',-class=>'DataIn', -re
+adonly=>'readonly'),
            br,
            "<label for='CallCompleteDateFld'>Call Complete </label>",
              textfield(-name=>'CallCompleteDateFld',-value=>$CallComp
+leteDate,-size=>10,-maxlength=>10,
                          -id=>'CallCompleteDateFld',-class=>'DataIn',
+ -readonly=>'readonly'),
            br,
            "<label for='SampleStatusDue'>Sample Status </label>",
            checkbox(-name=>'SampleStatusDue',-checked=>$SampleStatusD
+ue?1:0,
                        -value=>$SampleStatusDue,-label=>'Waiting/Clie
+nt', -readonly=>'readonly'),
            ' ',
            checkbox(-name=>'SampleStatusReceived',-checked=>$SampleSt
+atusReceived?1:0,
                        -value=>$SampleStatusReceived,-label=>'Receive
+d', -readonly=>'readonly'),
            ' ',
            checkbox(-name=>'SampleStatusSentToPSU',-checked=>$SampleS
+tatusSentToPSU?1:0,
                        -value=>$SampleStatusSentToPSU,-label=>'Sent T
+o PSU', -readonly=>'readonly'),
            br,
            "<label for='QuestionFld'>Question</label>",
                textarea(-name=>'QuestionFld',-value=>$Question,-rows=
+>10,-columns=>50,-class=>'DataIn', 
                        -readonly=>'readonly'),
            br,br,br,br,br,br,br,br,br,
            "<label for='AnswerFld'>Answer</label>",
                textarea(-name=>'AnswerFld',-value=>$Answer,-rows=>10,
+-columns=>50,-class=>'DataIn', 
                        -readonly=>'readonly'),
            br,br,br,br,br,br,br,br,br,
            "<label for='ContactMethodPhone'>Contact Methods</label>",
            checkbox(-name=>'ContactMethodPhone',-checked=>$ContactMet
+hodPhone?1:0,
                        -value=>'1',-label=>'Phone', -readonly=>'reado
+nly'),
            ' ',
            checkbox(-name=>'ContactMethodWalkIn',-checked=>$ContactMe
+thodWalkIn?1:0,
                        -value=>'1',-label=>'Walk In', -readonly=>'rea
+donly'),
            ' ',
            checkbox(-name=>'ContactMethodEmail',-checked=>$ContactMet
+hodEmail?1:0,
                        -value=>'1',-label=>'Email', -readonly=>'reado
+nly'),
            ' ',
            checkbox(-name=>'ContactMethodEvent',-checked=>$ContactMet
+hodEvent?1:0,
                        -value=>'1',-label=>'Event', -readonly=>'reado
+nly'),
            br,
            "<label for='IPVerbally'>Information Provided</label>",
            checkbox(-name=>'IPVerbally',-checked=>$InfoProvidedVerbal
+ly?1:0,
                        -value=>'1',-label=>'Verbally', -readonly=>'re
+adonly'),
            " ",
            checkbox(-name=>'IPFaxed',-checked=>$InfoProvidedFaxed?1:0
+,
                        -value=>'1',-label=>'Faxed', -readonly=>'reado
+nly'),
            " ",
            checkbox(-name=>'IPMailed',-checked=>$InfoProvidedMailed?1
+:0,
                        -value=>'1',-label=>'Mailed', -readonly=>'read
+only'),
            " ",
            checkbox(-name=>'IPHandout',-checked=>$InfoProvidedHandout
+?1:0,
                        -value=>'1',-label=>'Handout', -readonly=>'rea
+donly'),
            " ",
            checkbox(-name=>'IPWebsite',-checked=>$InfoProvidedWebsite
+?1:0,
                        -value=>'1',-label=>'Website', -readonly=>'rea
+donly'),
            br,
            '<label for="MGFld">Initial Call MG </label>',
            textfield(-name=>'MGFld',-value=>$MasterGardener,-size=>30
+,-maxlength=>50,-id=>'MGFld',
                          -class=>'DataIn', -readonly=>'readonly'),
            br,
            '<label for="CallBackMGFld">Call Back MG </label>',
            textfield(-name=>'CallBackMGFld',-value=>$MGCallBack,-size
+=>30,-maxlength=>50,-id=>'CallBackMGFld',
                          -class=>'DataIn', -readonly=>'readonly'),
            br,
            "<label for='FactSheetsFld'>Fact Sheets </label>",
            textfield(-name=>'FactSheetsFld',-value=>$FactSheets,-size
+=>2,-maxlength=>2,-id=>'FactSheetsFld',
                          -class=>'DataIn', -readonly=>'readonly'),
            br,
            "<label for='TopicFld'>Topic </label>",
            textfield(-name=>'TopicFld',-value=>$Topic,-size=>20,-maxl
+ength=>30,-id=>'TopicFld',
                          -class=>'DataIn', -readonly=>'readonly');

    print start_form(-method=>"POST",
                -name=>"NextForm",
                -id=>"NextForm",
                -action=>"http://www.hortline.rbhyland.org/SearchConta
+cts.cgi");
    print br,submit(-name=>'Next',-value=>'Next');
    print br,submit(-name=>'Prev',-value=>'Prev');
    print end_form;

}

sub getIDs {
    $SrchStr = param('SearchFld');
    $dbh = DBI->connect("DBI:mysql:database=hortline;host=mysql.hortli
+ne.rbhyland.org","rbhyland","dh_R95w")
                        or &dienice("Database logon failed: $DBI::errs
+tr\n");
    $selectstr = "SELECT * ".
                    "FROM Contacts ".
                    "WHERE County = ?; ";
    $sth = $dbh->prepare("$selectstr");
    $sth->execute($County);
    
    while ( @row = $sth->fetchrow_array() ) {
        my $row = "@row";
        if (index(uc($row),uc($SrchStr)) >=0) {
            push(@ContactIDList, $row[0]);
        }
    }
    warn "Data fetching terminated early by error: $DBI::errstr\n"
      if $DBI::err;
    
    print "@ContactIDList",br;
}

sub dienice {
    my ($msg) = @_;
    print "<b>$msg</b>";
    exit;
}

sub dbdie {
    my ($errmsg) = "$DBI::errstr<br />";
    &dienice($errmsg);
}

[download]

Replies are listed 'Best First'.
Re: Global Variables Not Acting Global
by anonymized user 468275 (Curate) on Apr 21, 2011 at 11:55 UTC
    I could be wrong, but I get the strong impression that you are expecting the value of the variable to persist between http requests. CGI::Session contains methods for storing and retrieving data in such cases.

    One world, one people

[reply]
      You're right, I was, foolishly, expecting that, but I don't know why. I knew that this was a stateless environment. Thanks for the tip about CGI::Session. I will check it out.
[reply]
Re: Global Variables Not Acting Global
by Eliya (Vicar) on Apr 21, 2011 at 11:51 UTC

    Are you running the CGI program persistently (such as under mod_perl), or are you running it as a "normal" CGI program?  In the latter case, the process terminates after every HTTP request, and with it all variables' values are gone...

[reply]
Re: Global Variables Not Acting Global
by bart (Canon) on Apr 21, 2011 at 11:10 UTC
    The value of $CurIDPtr only changes if param('Next') or param('Back') is set. Maybe neither is happening?

    And perhaps what you really want is to pass a parameter for that variable through the form, otherwise it'll always be 0, 1, or -1.

[reply]
[d/l]
      Next and Prev are being set. I can add another parameter, but shouldn't a global variable be global? Does the if block override a global variable's value?
[reply]
        No, in Perl a variable is global, anywhere, unless there's a my declaration in a surrounding block. I don't think variable scope is your problem.
[reply]
        If both are set, of course the value is 0 again -- one of them takes care of increment, one of decrementing. Both add up to 0 in the end.
        Perl 6 - second systems done right
[reply]
Re: Global Variables Not Acting Global
by moritz (Cardinal) on Apr 21, 2011 at 11:39 UTC
[reply]
Re: Global Variables Not Acting Global
by LanX (Saint) on Apr 21, 2011 at 12:08 UTC
    What's your problem?

    Please demonstrate it in a condensed piece of code and plz make clear if your talking about one invocation of your CGI or persistent sessions.

    In the latter case (i.e. mod-perl, FCGI, ...), there are issues regarding package and lexical variables.

    Cheers Rolf

[reply]
      I was expecting a global variable, $CurIDPtr, to maintain its value like a session variable. anonymized user 468275 put his finger on the problem.
[reply]
        here a simple example of a persistent variable $count while using CGI::Fast

        use strict;
use warnings;
use CGI::Fast;
 
our $count = 0;
 
while ( my $q = new CGI::Fast ) {
    $count++;
    print $q->header( "text/plain" ),
          "You are request number $count. Have a good day!\n";
}

        [download]

        (taken from O'Reilly's CGI book and modernized )

        Cheers Rolf

[reply]
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