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Re: [PBML] returning arrays and hashes from a subroutine

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  • Charles K. Clarkson
    ... So this is what Japhy meant. Shame on you Japhy, I can t believe you d let Mark do it this way. :) ... my $sql = SELECT doc_name FROM $table WHERE
    Message 1 of 12 , May 2, 2002
      "markveerman" <mark@...> wrote:

      : I figured it out! Although, I don't really understand the, but
      : here's what it was:
      :
      : Below within the sub I originally had: my @fieldnames = $db-
      : >FieldNames(); return @fieldnames; When I removed the word "my",
      : @fieldnames was returned correctly. Also, I didn't realize you could
      : call the function like @array = function() - so that was helpful too.
      :
      : thanks for your help japhy!

      So this is what Japhy meant. Shame on you Japhy, I
      can't believe you'd let Mark do it this way. :)

      : use Win32::ODBC;
      : my $dsn = "mysql";
      : my $table = "table";
      : my $sql = "SELECT doc_name FROM " . $table . " WHERE status = 'Q'";

      my $sql = "SELECT doc_name FROM $table WHERE status = 'Q'";

      : odbc($dsn, $table, $sql);

      my @field_names = odbc($dsn, $sql) ||
      die "There's an uncaught error in odbc()";

      : foreach $fieldnames(@fieldnames){
      : print $fieldnames . "\n";
      : }

      print "$_\n" foreach @field_names;

      : sub odbc {
      : my ($dsn, $table, $sql) = @_;
      : use Win32::ODBC;

      sub odbc {
      my ($dsn, $sql) = @_;

      : my $db = new Win32::ODBC($dsn);
      :
      : if (!$db){
      : die "Error connecting: " . Win32::ODBC::Error() . "\n";
      : }

      my $db = new Win32::ODBC($dsn) ||
      die 'Error connecting: ', Win32::ODBC::Error();

      : if ($db->Sql($sql)) {
      : print "Error submitting SQL statement: " . $db->Error
      : () . "\n" . $sql;
      : }

      if ( $db->Sql($sql) ) {
      print "Error submitting SQL statement: $db->Error\n$sql";
      # Are you sure you don't want to die here?
      }

      : else{
      : @fieldnames = $db->FieldNames();
      : return @fieldnames;

      return $db->FieldNames();
      : }

      return;


      HTH,

      Charles K. Clarkson
      --
      Head Bottle Washer,
      Clarkson Energy Homes, Inc.

      CJ Web Work - Domains for Real Estate Investors.
      E Pluribus Unum -- One from many.
    • Charles K. Clarkson
      ... When I started with perl last year, almost everything I managed to get working was an example of poor coding. A subroutine should be able to be pulled out
      Message 2 of 12 , May 2, 2002
        "markveerman" <mark@...> wrote:

        : Thanks Charles - Are you telling me that even though it
        : works it's not good code? :-).

        When I started with perl last year, almost everything I
        managed to get working was an example of poor coding.
        A subroutine should be able to be pulled out of the
        program it was written in and placed in another and run
        with minimal adjustment.

        When writing a subroutine, think of it as if a manager
        just handed you an assignment. You have no idea how this
        sub will be used in the program. You know what it should
        accept, what it should return, and what it should do.

        You can cut some corners for short programs, but the
        larger and more complex your script gets the more you
        need to follow this or a more refined approach to
        building subroutines.

        : As if it's not totally obvious - I'm a novice.

        A novice what?

        : > So this is what Japhy meant. Shame on you Japhy, I
        : > can't believe you'd let Mark do it this way. :)
        :
        : In defense of Japhy, today was the first day I've ever
        : written a sub routine, so the issues with scoping and
        : local/global variables is entirely new.

        Is was meant as a joke. I knew Japhy didn't mean want
        you thought he did.


        HTH,

        Charles K. Clarkson
        --
        Head Bottle Washer,
        Clarkson Energy Homes, Inc.

        CJ Web Work - Domains for Real Estate Investors.
        E Pluribus Unum -- One from many.
      • Jeff 'japhy' Pinyan
        ... No! You re not returning anything then! You re just setting a global array. The concept of returning something from a function is that you ACTUALLY send
        Message 3 of 12 , May 2, 2002
          On May 2, markveerman said:

          >Below within the sub I originally had: my @fieldnames = $db-
          >>FieldNames(); return @fieldnames; When I removed the word "my",
          >@fieldnames was returned correctly. Also, I didn't realize you could
          >call the function like @array = function() - so that was helpful too.

          No! You're not returning anything then! You're just setting a global
          array. The concept of returning something from a function is that you
          ACTUALLY send content FROM the function BACK to the program. Also, your
          approach of removing 'my' makes your code possibly less safe, since you
          might end up ruining some OTHER @fieldnames array. Using my() helps keep
          your variables scoped properly.

          Compare:

          sub sum {
          $x = 0;
          for (@_) { $x += $_ }
          }

          sub set_sum {
          my $x = 0;
          for (@_) { $x += $_ }
          return $x;
          }

          sum(1,2,4,8);
          my $n = set_sum(1,3,5,7);

          The first function sets a global variable $x with the value 15; the second
          stores the value 16 in $n. With the first method, you have no control
          over WHERE the data goes -- the function does. With the second method,
          YOU have control where the data.

          > else{
          > @fieldnames = $db->FieldNames();
          > return @fieldnames;
          > }

          There's no point in returning @fieldnames. You're not returning it TO
          anything.

          --
          Jeff "japhy" Pinyan japhy@... http://www.pobox.com/~japhy/
          RPI Acacia brother #734 http://www.perlmonks.org/ http://www.cpan.org/
          ** Look for "Regular Expressions in Perl" published by Manning, in 2002 **
          <stu> what does y/// stand for? <tenderpuss> why, yansliterate of course.
          [ I'm looking for programming work. If you like my work, let me know. ]
        • markveerman
          ... global ... you ... your ... you ... helps keep ... Okay, I think I understand what you re saying, however, If I don t return @fieldnames, then I can t do
          Message 4 of 12 , May 2, 2002
            > No! You're not returning anything then! You're just setting a
            global
            > array. The concept of returning something from a function is that
            you
            > ACTUALLY send content FROM the function BACK to the program. Also,
            your
            > approach of removing 'my' makes your code possibly less safe, since
            you
            > might end up ruining some OTHER @fieldnames array. Using my()
            helps keep
            > your variables scoped properly.

            Okay, I think I understand what you're saying, however, If I don't
            return @fieldnames, then I can't do anything with them ... like print
            them out. I'm going to be using this function to query a db and
            return the results. I can't do anything with the results within the
            function, because I want it to remain generic enough so I can use it
            for all my db queries. So, in order for me to USE the info I get
            from the queries, I've got to return the data BACK to the program.

            > There's no point in returning @fieldnames. You're not returning it
            TO anything.

            I thought I was returning it to the program so I could then loop
            through it and print out the field names. Bear with me, I'm really
            trying to understand :-).
            /mark

            >
            > --
            > Jeff "japhy" Pinyan japhy@p...
            http://www.pobox.com/~japhy/
            > RPI Acacia brother #734 http://www.perlmonks.org/
            http://www.cpan.org/
            > ** Look for "Regular Expressions in Perl" published by Manning, in
            2002 **
            > <stu> what does y/// stand for? <tenderpuss> why, yansliterate of
            course.
            > [ I'm looking for programming work. If you like my work, let me
            know. ]
          • markveerman
            Thanks Charles - Are you telling me that even though it works it s not good code? :-). As if it s not totally obvious - I m a novice. /mark ... In defense of
            Message 5 of 12 , May 2, 2002
              Thanks Charles - Are you telling me that even though it works it's
              not good code? :-). As if it's not totally obvious - I'm a novice.
              /mark

              > So this is what Japhy meant. Shame on you Japhy, I
              > can't believe you'd let Mark do it this way. :)

              In defense of Japhy, today was the first day I've ever written a sub
              routine, so the issues with scoping and local/global variables is
              entirely new.

              Thanks to you both for the assistance.
              /mark
            • Jeff 'japhy' Pinyan
              ... Gaaah! No, Mark misunderstood my code, Charles. Mark, the return() function does not tell Perl that variables you used in your function can be used
              Message 6 of 12 , May 2, 2002
                On May 2, Charles K. Clarkson said:

                >"markveerman" <mark@...> wrote:
                >
                >: I figured it out! Although, I don't really understand the, but
                >: here's what it was:
                >:
                >: Below within the sub I originally had: my @fieldnames = $db-
                >: >FieldNames(); return @fieldnames; When I removed the word "my",
                >: @fieldnames was returned correctly. Also, I didn't realize you could
                >: call the function like @array = function() - so that was helpful too.
                >:
                >: thanks for your help japhy!
                >
                > So this is what Japhy meant. Shame on you Japhy, I
                >can't believe you'd let Mark do it this way. :)

                Gaaah! No, Mark misunderstood my code, Charles.

                Mark, the return() function does not tell Perl that variables you used in
                your function can be used OUTSIDE the function. It does nothing of the
                sort. All it does is tell Perl that it can put the VALUES of those
                variables in place you can get them from; specifically, from the return
                value of the function:

                sub cube {
                my $n = shift;
                return $n ** 3;
                }

                $big = cube(1234);

                The function cube() RETURNS ONE VALUE. If you don't use the return value
                somehow (like storing it in a variable, or printing it) then it
                disappears.

                Here are some examples to see if it becomes clear to you.

                sub foobar {
                my @bah = (1, 2, 3, 4);
                return @bah;
                }

                my @bah = (5, 6);
                foobar();
                print "@bah\n"; # 5 6

                ###########################

                sub foobar {
                my @bah = (1, 2, 3, 4);
                }

                my @bah = (5, 6);
                foobar();
                print "@bah\n"; # 5 6

                ###########################

                sub foobar {
                my @bah = (1, 2, 3, 4);
                return @bah;
                }

                my @bah = (5, 6);
                @bah = foobar();
                print "@bah\n"; # 1 2 3 4

                ###########################

                sub foobar {
                my @bah = (1, 2, 3, 4);
                }

                my @bah = (5, 6);
                @bah = foobar(); # foobar() returns the last thing evaluated, @bah
                print "@bah\n"; # 1 2 3 4 (but only because you're lucky!)

                ###########################

                sub foobar {
                @bah = (1, 2, 3, 4); # THIS SETS THE OUTSIDE @bah (bad idea)
                return @bah;
                }

                my @bah = (5, 6);
                foobar();
                print "@bah\n"; # 1 2 3 4

                ###########################

                sub foobar {
                my @bah = (1, 2, 3, 4); # DITTO
                }

                my @bah = (5, 6);
                foobar();
                print "@bah\n"; # 5 6

                --
                Jeff "japhy" Pinyan japhy@... http://www.pobox.com/~japhy/
                RPI Acacia brother #734 http://www.perlmonks.org/ http://www.cpan.org/
                ** Look for "Regular Expressions in Perl" published by Manning, in 2002 **
                <stu> what does y/// stand for? <tenderpuss> why, yansliterate of course.
                [ I'm looking for programming work. If you like my work, let me know. ]
              • Franki
                well you just taught me something as well.. I hadn t really given it much thought, but now that I have, its kinda obvious and I am ashamed of myself for not
                Message 7 of 12 , May 3, 2002
                  well you just taught me something as well..

                  I hadn't really given it much thought, but now that I have, its kinda
                  obvious and I am ashamed of myself for not realising it..

                  I had been wondering why not all of my "return" code works...

                  Thankyou..


                  regards

                  Frank

                  -----Original Message-----
                  From: Jeff 'japhy' Pinyan [mailto:japhy@...]
                  Sent: Friday, 3 May 2002 10:16 AM
                  To: perl-beginner@yahoogroups.com
                  Subject: Re: [PBML] returning arrays and hashes from a subroutine


                  On May 2, Charles K. Clarkson said:

                  >"markveerman" <mark@...> wrote:
                  >
                  >: I figured it out! Although, I don't really understand the, but
                  >: here's what it was:
                  >:
                  >: Below within the sub I originally had: my @fieldnames = $db-
                  >: >FieldNames(); return @fieldnames; When I removed the word "my",
                  >: @fieldnames was returned correctly. Also, I didn't realize you could
                  >: call the function like @array = function() - so that was helpful too.
                  >:
                  >: thanks for your help japhy!
                  >
                  > So this is what Japhy meant. Shame on you Japhy, I
                  >can't believe you'd let Mark do it this way. :)

                  Gaaah! No, Mark misunderstood my code, Charles.

                  Mark, the return() function does not tell Perl that variables you used in
                  your function can be used OUTSIDE the function. It does nothing of the
                  sort. All it does is tell Perl that it can put the VALUES of those
                  variables in place you can get them from; specifically, from the return
                  value of the function:

                  sub cube {
                  my $n = shift;
                  return $n ** 3;
                  }

                  $big = cube(1234);

                  The function cube() RETURNS ONE VALUE. If you don't use the return value
                  somehow (like storing it in a variable, or printing it) then it
                  disappears.

                  Here are some examples to see if it becomes clear to you.

                  sub foobar {
                  my @bah = (1, 2, 3, 4);
                  return @bah;
                  }

                  my @bah = (5, 6);
                  foobar();
                  print "@bah\n"; # 5 6

                  ###########################

                  sub foobar {
                  my @bah = (1, 2, 3, 4);
                  }

                  my @bah = (5, 6);
                  foobar();
                  print "@bah\n"; # 5 6

                  ###########################

                  sub foobar {
                  my @bah = (1, 2, 3, 4);
                  return @bah;
                  }

                  my @bah = (5, 6);
                  @bah = foobar();
                  print "@bah\n"; # 1 2 3 4

                  ###########################

                  sub foobar {
                  my @bah = (1, 2, 3, 4);
                  }

                  my @bah = (5, 6);
                  @bah = foobar(); # foobar() returns the last thing evaluated, @bah
                  print "@bah\n"; # 1 2 3 4 (but only because you're lucky!)

                  ###########################

                  sub foobar {
                  @bah = (1, 2, 3, 4); # THIS SETS THE OUTSIDE @bah (bad idea)
                  return @bah;
                  }

                  my @bah = (5, 6);
                  foobar();
                  print "@bah\n"; # 1 2 3 4

                  ###########################

                  sub foobar {
                  my @bah = (1, 2, 3, 4); # DITTO
                  }

                  my @bah = (5, 6);
                  foobar();
                  print "@bah\n"; # 5 6

                  --
                  Jeff "japhy" Pinyan japhy@... http://www.pobox.com/~japhy/
                  RPI Acacia brother #734 http://www.perlmonks.org/ http://www.cpan.org/
                  ** Look for "Regular Expressions in Perl" published by Manning, in 2002 **
                  <stu> what does y/// stand for? <tenderpuss> why, yansliterate of course.
                  [ I'm looking for programming work. If you like my work, let me know. ]



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