vec and unpack

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

I have doubt about vec function .
+ what vec() does here ?
+ Without calling vec() function also this piece of code work fine what i have expected .
+ split (//, unpack("b*", $OutputBuffer)) what it does?

use IO::Select;
use IO::Socket;

$lsn = new IO::Socket::INET(proto => 'tcp', Listen => 1,  LocalAddr =>
+ '192.168.6.92:9090', Reuse => 1);
print "Error in socket :$!\n";
$sel = new IO::Select( $lsn );

$i = 0;

$IPHASH= {};

while(@ready = $sel->can_read) {
    foreach $fh (@ready) {
        if($fh == $lsn) {

            # Create a new socket
            $new = $lsn->accept;
                        $HostAdd = $new->peername();
                        ($Port , $Myadd) = sockaddr_in($HostAdd);
                        $IPAdd = inet_ntoa($Myadd);
                        $sel->add($new);
                        $IPHASH->{"$IPAdd"} = $new;

        }
        else {
            # Process socket
                        $InputBuffer;
                        $OutputBuffer;
                        $Delay = 0.1;
                         vec($InputBuffer, fileno($fh),1)=1;
                         ($Found,  $Temp)  = select($OutputBuffer=$Inp
+utBuffer, undef, undef, $Delay);

                        my (@Bits)  = split (//,unpack("b*",
 $OutputBuffer));
  $handle = fileno($fh);
                          recv ($fh, $Received_Message, 20, 0);
                          $HostAdd = $new->peername();
                          ($Port , $Myadd) = sockaddr_in($HostAdd);
                          $IPAdd = inet_ntoa($Myadd);
                          $fh =  $IPHASH->{$Received_Message};
                          #vec($InputBuffer, fileno($fh), 1)=1;
                          #($Found,  $Temp)  = select($OutputBuffer=$I
+nputBuffer, undef, undef, $Delay);

                          # my (@Bits)  = split (//, unpack("b*", $Out
+putBuffer));
                          # $handle = fileno($fh);
                          print "::: $Received_Message :::: \n";
                          $fh->autoflush(1);
            # Maybe we have finished with the socket
            $sel->remove($fh);
            $fh->close;
        }
                $i++;
    }
}
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Replies are listed 'Best First'.
Re: vec and unpack by ikegami (Patriarch) on Nov 24, 2008 at 08:23 UTC
what vec() does here ? Tells `select` to which file handles to pay attention. By the way, IO::Select provides a much better interface than `select`. Without calling vec() function also this piece of code work fine what i have expected . Because the `select` is redundant with the `select` in `can_read`. split (//, unpack("b", $OutputBuffer)) what it does?* Nothing, `@Bits` is never used.	[reply] [d/l] [select]
Re: vec and unpack by Corion (Patriarch) on Nov 24, 2008 at 08:19 UTC
For vec see perldoc -f vec and for this specific use of vec see the select documentation, which has just this line together with the explanation. For unpack see unpack and pack, and possibly perlpacktut.	[reply]
Re: vec and unpack by lakshmananindia (Chaplain) on Dec 04, 2008 at 10:43 UTC
*split (//, unpack("b", $OutputBuffer)) what it does** From the vec documentation To transform a bit vector into a string or list of 0's and 1's, use $bits = unpack("b", $vector); @bits = split(//, unpack("b", $vector)); We cannot print vector variables directly. In sockets program which uses select will use vec to set a bit. So if you want to print the bits we cannot print it directly. For that purpose we will use the unpack.	[reply]