simple reference

kevind0718 has asked for the wisdom of the Perl Monks concerning the following question:

Hello Wise Monks:

I have confused myself with a simple pass by reference issue. Please consider the code below:

As you can see in the subroutine, $yr, $mth , $dt get set. But when I return the values are lost. Well they are lost to me.

What am I doing wrong?

Thanks for your kind assistance.

KD

sub maxFileDate {
  my  ( $filePrefix_In, @entries_In, $yr_ref, $mth_ref,  $dt_ref );
   
  ( $filePrefix_In, @entries_In, $yr_ref, $mth_ref, $dt_ref )  = @_ ;
  
  
   my   $entry;
   my   @fields;
   my   @fileName;
   
   print "fileName Prefix: " .  $filePrefix_In . "\n" ;
   ##print Dumper @entries_In  ; 
   
   
   my $maxdate = 20000101;
   foreach  $entry (@entries_In) {  
     ##print  "$entry  \n  ";
     chomp $entry;
     @fields = split /\s+/, $entry;
     if ( $fields[0] =~ m/^-/)  {
       # ** ** ** **  
       #this a file entry
       if ($fields[-1] =~ m/^$filePrefix_In/)  {
          @fileName  =  split /\.|_/ , $fields[-1];
          print Dumper @fileName   ; 
          print "file name: " .  $fields[-1] .   "   date part: " .  $
+fileName[4]. $fileName[5]. $fileName[6]. "\n";
          if (  ('20'.  $fileName[4]. $fileName[5]. $fileName[6]) >  $
+maxdate ) {
              $maxdate  =  ('20'.  $fileName[4]. $fileName[5]. $fileNa
+me[6]) ;
              $$yr_ref   = $fileName[4];
              $$mth_ref  = $fileName[5];
              $$dt_ref   = $fileName[6];
          }
       }   ##file name like 
     }   ##file entries
       
       
   }   ## for each entry       
   
   print "yr " . $yr_ref  . "\n" ;
   print "mth". $mth_ref . "\n" ;
   print "dt " . $dt_ref  . "\n" ;
   
   print "yr " . $$yr_ref  . "\n" ;
   print "mth". $$mth_ref . "\n" ;
   print "dt " . $$dt_ref  . "\n" ;
   


   ##$maxdate;

}  # maxFileDate
[download]

I call the above as follows:

    if ( !defined( $datein ) ) {

    maxFileDate('WSB826TB', @entries, \$yr, \$mth, \$dt );

  } # no date passed in
  else {
  
    $datea = $datein;
  }
    
  print "\nDownload WSB826TB for date: " . $yr. $mth. $dt . "\n";
[download]

It produces the following results:

C:\HFAccess\devPostgresql>perl -w xxx_ftpgetTest.pl xxx_ftp.prop
    Properties File: xxx_ftp.prop.
Properties
         FTPServer = ftp.xxx.ml.com
         RemoteDirectory = /outgoing
         User Id = mysecretid
         LocalServer =
         LocalDirectory = C:\HFAccess\xxxx
         GPG_HomeDirectory = Q:\Downloads\gnupg\keys
Remote Directory: /outgoing
fileName Prefix: WSB826TB
$VAR1 = 'WSB826TB';
$VAR2 = 'CST238PO';
$VAR3 = 'CSV';
$VAR4 = 'asc';
$VAR5 = '09';
$VAR6 = '04';
$VAR7 = '21';
$VAR8 = '01';
$VAR9 = '10';
file name: WSB826TB.CST238PO.CSV.asc.09.04.21_01.10   date part: 09042
+1
$VAR1 = 'WSB826TB';
$VAR2 = 'CST238PO';
$VAR3 = 'CSV';
$VAR4 = 'asc';
$VAR5 = '09';
$VAR6 = '04';
$VAR7 = '22';
$VAR8 = '00';
$VAR9 = '54';
file name: WSB826TB.CST238PO.CSV.asc.09.04.22_00.54   date part: 09042
+2
$VAR1 = 'WSB826TB';
$VAR2 = 'CST238PO';
$VAR3 = 'CSV';
$VAR4 = 'asc';
$VAR5 = '09';
$VAR6 = '04';
$VAR7 = '23';
$VAR8 = '02';
$VAR9 = '43';
file name: WSB826TB.CST238PO.CSV.asc.09.04.23_02.43   date part: 09042
+3
$VAR1 = 'WSB826TB';
$VAR2 = 'CST238PO';
$VAR3 = 'CSV';
$VAR4 = 'asc';
$VAR5 = '09';
$VAR6 = '04';
$VAR7 = '24';
$VAR8 = '01';
$VAR9 = '33';
file name: WSB826TB.CST238PO.CSV.asc.09.04.24_01.33   date part: 09042
+4
$VAR1 = 'WSB826TB';
$VAR2 = 'CST238PO';
$VAR3 = 'CSV';
$VAR4 = 'asc';
$VAR5 = '09';
$VAR6 = '04';
$VAR7 = '25';
$VAR8 = '00';
$VAR9 = '26';
file name: WSB826TB.CST238PO.CSV.asc.09.04.25_00.26   date part: 09042
+5
yr SCALAR(0x1ae256c)
mthSCALAR(0x1ae2578)
dt SCALAR(0x1ae2584)
yr 09
mth04
dt 25
Use of uninitialized value in concatenation (.) or string at xxx_ftpge
+tTest.pl line 153.
Use of uninitialized value in concatenation (.) or string at xxx_ftpge
+tTest.pl line 153.
Use of uninitialized value in concatenation (.) or string at xxx_ftpge
+tTest.pl line 153.

Download WSB826TB for date:

C:\HFAccess\devPostgresql>
[download]

Comment on simple reference Select or Download Code

Replies are listed 'Best First'.
Re: simple reference by moritz (Cardinal) on Apr 27, 2009 at 21:42 UTC
`( $filePrefix_In, @entries_In, $yr_ref, $mth_ref, $dt_ref ) = @_ ;` `$yr_ref` and the following variables will never get any values here, because all rest values from `@_` are slurped into `@entries_In`. Either re-order your arguments, or use an array reference, or pass a hash of all values (including an array reference) around. Please start all your perl scripts with `use strict; use warnings;` [download] I think it would have caught that error. Also `print Dumper @fileName ;` is much more informative if you write `print Dumper \@fileName;` instead.	[reply] [d/l] [select]
Re: simple reference by lostjimmy (Chaplain) on Apr 27, 2009 at 21:41 UTC
I think your problem has to do with the following line: `($filePrefix_In, @entries_In, $yr_ref, $mth_ref, $dt_ref ) = @_`. What's going to happen is `@entries_In` is going to slurp up the remaining arguments, which means that `$yr_ref`, `$mth_ref`, and `$dt_ref` are going to be undef. You can solve this by reordering your arguments (i.e. `($filePrefix_In, $yr_ref, $mth_ref, $dt_ref, @entries_In)`) or by passing the entries array by reference instead.	[reply] [d/l] [select]
Re: simple reference by shmem (Chancellor) on Apr 27, 2009 at 21:46 UTC
`( $filePrefix_In, @entries_In, $yr_ref, $mth_ref, $dt_ref ) = @_ ;` [download] If you pass around an array, pass it as a reference, or pass it as the last item, since it will get flattened into a list. Your assignment to `@entries_In` gobbles up the references passed after the array, so at the top of your subroutine `$yr_ref, $mth_ref, $dt_ref` are all uninitialized. See perlsub. Re-ordering your subroutine arguments makes a difference: `( $filePrefix_In, $yr_ref, $mth_ref, $dt_ref, @entries_In ) = @_ ;` [download] Now `@entries_In` gets the rest of `@_` - as before, but there aren't any more items after the original (now flattened) array.	[reply] [d/l] [select]