in reply to uninitialized value in concatenation

mnlight wrote:

Can anyone explain why I am recieving this error.
Use of uninitialized value in concatenation (.) or string at Signup.pl line 46...

The short answer is "yes, I can explain why." You have an unitialized value in a concatenation or string. The longer answer is, "no, I don't know why you have an unitialized value." I don't know what your line numbers are, so I can't tell where the value is. Further, while I could try to figure out the offsets from your error messages and correlate those to print statements in your code, I'm not going to do that.

If you have a halfway decent editor (no, I'm not talking about Notepad), you should be able to see your line numbers. Since you're not using HERE docs (which can obscure the problem), you should be able to point almost perfectly to the line where you have an unitialized value. For example:

$ perl -e '
use strict;
use warnings;
my $x;
print $x;'
Use of uninitialized value in print at -e line 5.

[download]

I can see at a glance that the lone print statement is line 5 and, if I had a problem, I could tell the monks "Look, there's where I get the error".

So, try reporting where the error is and we'll try to narrow it down for you (though I suspect that it lies in your SQL returning nothing).

Update: I tried refactoring and cleaning up your code a little bit:

$user = $dbh->quote( $user );
my ( $field, $sub_parent ) = $parent eq 'Father'
    ? ( 'Father', "'Mother'" )
    : ( 'Mother', "'Father'" );

$sth = $dbh->prepare ("select $field from Roster where User = $user");
$sth->execute ();
my $name = $sth->fetchrow_array;

if ($name eq ""){
    $sth = $dbh->prepare ("select $sub_parent from Roster where User =
+ $user");
    $sth->execute ();
    $name = $sth->fetchrow_array;
} #end chk for not parent if statement.

print $query->h1({-align=>'center'},"THANK YOU FOR SIGNING UP $name");

$sth = $dbh->prepare ("select distinct Volunteer from Volunteer where 
+Volunteer = ? and Date = ?");
foreach my $date ( @volunteer_date ) 
{
    $sth->execute ( $name, $date );
    my $chk = $sth->fetchrow_array;

    if ($chk eq $name)
    {
        print $query->h1({-align=>'center'}, "You are already signed u
+p for this date: $date");
    } #end if statement
    else
    {
        $sth = $dbh->prepare ("select max(Number) from Volunteer where
+ Date = ? and Volunteer = 'TBD'");
        $sth->execute ($date );

[download]

After doing this, I saw that you are not using strict and you have some serious scoping issues. These scoping issues make this difficult. As I see from your code below, the problem lies in $user not being initialized.

$sth = $dbh->prepare ("select Mother from Roster where User = \'$user\
+'");

[download]

Thus, your problem occurred before the snipped that you presented us with. Also, note in my cleanup above that I used the $dbh->quote method. This will save you much grief, rather than trying to escape the data with single quotes (if the data contains single quotes, your escaping it will fail, for example). I suggest you read the DBI documentation very carefully.

Cheers,
Ovid

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Replies are listed 'Best First'.
Re: (Ovid) Re: uninitialized value in concatenation
by mnlight (Scribe) on Jan 14, 2002 at 22:54 UTC
    I'm sorry about not being more specific.
    here is the code with the line numbers. 
    #Selecting parents name to identify as volunteer.
     35    if ($parent eq "Father")
     36    {
     37         $sub_parent = "Mother";
     38         $sth = $dbh->prepare ("select Father from Roster where
+ User = \'$user\'");
     39         $sth->execute ();
     40 
     41 $name = $sth->fetchrow_array;
     42    } #end if Father
     43    else
     44    {
     45         $sub_parent = "Father";
     46         $sth = $dbh->prepare ("select Mother from Roster where
+ User = \'$user\'");
     47         $sth->execute ();
     48 
     49 $name = $sth->fetchrow_array;
     50    } #end else Mother
     51 
     52 if ($name eq ""){
     53         $sth = $dbh->prepare ("select $sub_parent from Roster 
+where User = \'$user\'");
     54         $sth->execute ();
     55 
     56 $name = $sth->fetchrow_array;
     57 
     58 } #end chk for not parent if statement.
     59 
     60 print $query->h1({-align=>'center'},"THANK YOU FOR SIGNING UP 
+$name");
     61

    [download]
    I am certain it has something to do with returning an empty string from my sql as well but I don't know what that something is
[reply]
[d/l]

      When calling $sth->fetchrow_array in a scalar context, you're going to get back an array ref, possibly containing some other array refs (your result rows). So your test, if ($name eq "") {, should probably look more like, if ($name->[0][0] eq "") {, except that this completely disregards the case where no rows are returned.

      You might also factor out all of the common code and elminate unnecessary complexity:

      my $name = undef;

# store subparent for each parent
my %parent_hash = ( 'Father' => 'Mother',
                    'Mother' => 'Father' );

if (exists $parent_hash{$parent}) {
  my $sub_parent = $parent_hash{$parent};

  for my $col ( $parent, $sub_parent ) {
    my $sql = "select $col from Roster where User=?";

    my $rv = $dbh->selectcol_arrayref( $sql, undef, $user );
    if ( @$rv ) {  # any rows returned?
      $name = $rv->[0];  # take first one
      last;
    }
  }
}
# here, $name will be defined if one of above succeeded

# etc. ...

      [download]

      Also, why are you using prepared statements (e.g., prepare() and execute()) without placeholders ('?'). You can just call selectrow_arrayref($sql) (or in your case, selectcol_arrayref($sql) since the results will be a single column) to the same effect.

      Update: added placeholders, as per cfreak. What was I thinking?

      dmm

      If you GIVE a man a fish you feed him for a day
      But,       TEACH him to fish and you feed him for a lifetime
[reply]
[d/l]
[select]
        This code is not working because the sql is returning a '' value and the if statement is seeing it as being true. what can I change so it evaluates the '' as no value returned. 
        # store subparent for each parent
my %parent_hash = ( 'Father' => 'Mother',
                    'Mother' => 'Father' );

if (exists $parent_hash{$parent}) {
  my $sub_parent = $parent_hash{$parent};

  for my $col ( $parent, $sub_parent ) {
    my $sql = "select $col from Roster where User=?";
    my $rv = $dbh->selectcol_arrayref( $sql, undef, $user);
    if ( @$rv) {  # any rows returned?
      $name = $rv->[0];  # take first one
      last;
    }
  }
}

        [download]
[reply]
[d/l]
        When calling $sth->fetchrow_array in a scalar context, you're going to get back an array ref, possibly containing some other array refs (your result rows).

        It is not correct. $sth->fetchrow_array in a scalar context returns the value of the first field.

        --
        Ilya Martynov (http://martynov.org/)

[reply]
        In this 
        my $name = undef;

# store subparent for each parent
my %parent_hash = ( 'Father' => 'Mother',
                    'Mother' => 'Father' );

if (exists $parent_hash{$parent}) {
  my $sub_parent = $parent_hash{$parent};

  for my $col ( $parent, $sub_parent ) {
    my $sql = "select $col from Roster where User=?";

    my $rv = $dbh->selectcol_arrayref( $sql, undef, $user );
    if ( @$rv ) {  # any rows returned?
      $name = $rv->[0];  # take first one
      last;
    }
  }
}
# here, $name will be defined if one of above succeeded

        [download]
        what is the undef do inside the 
        my $rv = $dbh->selectcol_arrayref( $sql, undef, $user );

        [download]
[reply]
[d/l]
[select]
        Please explain how I can eliminate some of the complexity.
[reply]

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