in reply to Returning and passing data to and from subroutines

It would have been helpful to point out that lines 212 and 213 are:

 my @data       = shift;
 my $loop_count = 0;
 while (@data) {
  $data[$loop_count] =~ m{s/^\s*//}xms;#line 212
  $data[$loop_count] =~ m{s/\s*$//}xms;#line 213
  $loop_count++;
 }

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So first of all, shift gets _one scalar_ off the arguments. You can't pass arrays around like that in Perl, you pass lists. If you call a sub with an array as the argument, it comes in as a list. If you pass in *two* arrays, they get flattened into a single list of scalar arguments. Secondly, in Perl you can iterate over the elements of an array like so: 

foreach $element (@array) {
  do_stuff_to($element);
}

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so you don't need a loop counter at all. If you *do* need a loop counter (i.e. to synchronize two array walks), you would be better off doing something like 
for $index (0..$#array) { # $#array is the last index of @array
 do_stuff_to($array[$index]);
 do_stuff_to($other_array[$index]);
};

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Also your matches appear to be looking for some strange things. The s/// inside the m//, if it even works at all, is operating on $_, not on $data[$loop_count], I believe, which is unlikely to be what you want. m// should contain a regex, not code. s/// is code.

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Re^2: Returning and passing data to and from subroutines
by vendion (Scribe) on Jul 17, 2010 at 03:30 UTC

    So if I change the shift to @_ that would make it work for arrays but what if I need to pass something like a scalier or a hash? Is there a way to check/handle this other than making more than one sub that preforms the same task just taking different arguments? Sorry I was confused on the use of shift and I was under the impression that shift did exactly that.

[reply]

      If you call a sub with a single scalar, it's the same as calling it with a 1-element list. @_ will contain the one scalar, and you can get it with shift. If you want to call a sub with multiple arrays or hashes and not have them flattened, you need to use references, and you probably want to look at something like perlreftut. If you call a sub with a single array and you want to get all the elements out at once, you can use: 

      my @args=@_; # or my %args=@_ if you know it's going to be a hash

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      or 
      my ($arg1, $arg2, $arg3) = @_; # faster than (shift,shift,shift)

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      the second form there assumes you know how many arguments you're going to get, or don't care if some of them come back undef.
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[d/l]
[select]

        Thanks, the reason I ask is because some how I have done something wrong. When at the programs menu if I were to input lets say "10" it some how returns as a 1 then it fails the test causing my display_menu_error sub to be executed with this error "ERROR: illegal option: 1 selected" some where along the line the 10 I give the program is changed: 

        db_connect();    #Connect to the database if needed
while ( display_menu(), ( my $option = <> ) ) {
 print '$option before processing input: ' . $option # returns 10
 $option = process_input($option);
 print '$option after processing input: ' . $option # returns 1
 if ( ( $option !~ m{/^\d+$/}xms ) or ( $option <= 0 ) or ( $option > 
+10 ) ) {
  display_menu_error("ERROR: illegal option: $option selected\n");
  next;
 }
 print_form()     if $option == 1;
 print_edit()     if $option == 2;
 db_remove()      if $option == 3;
 db_fetch()       if $option == 4;
 print_all()      if $option == 5;
 print_report()   if $option == 6;
 db_check()       if $option == 7;
 leave_comment()  if $option == 8;
 leave_donation() if $option == 9;

 if ( $option == 10 ) {
  $dbh->disconnect;
  print "Quitter...\n";
  exit 0;
 }
}
...
sub process_input {

# takes in information and loops through testing the input for valid a
+lphanumeric characters.
 my @data = @_;
 for (@data) {
  chomp;
  s/^\s*//; # Have tried commenting out no change
  s/\s*$//; # Still somehow returns incorrect values
 }
 return @data;
}

        [download]
        I just can't see why it would be doing that to me like that
[reply]
[d/l]

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