in reply to Re: Re: Unpack for VMS binary files
in thread Unpack for VMS binary files

Whilst parsing the VMS binary file, I have unpacked it with the template: 
my $template="V2 v12";

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Where V/v are a long/short in "VAX" (little-endian) order. As I've already unpacked the data, there isn't a need to redo the unpack commands in the subroutine - just pass the low_long and high_long as is into the sub. There is one problem: the data in the binary file starts at 00:00:00 and ends at 23:40:40 for 1-1-2003. Printing out the output from the sub produces 11:00:00 through to 23:40:40 and _then_ 00:00:00 through to 10:59:40 for 2-1-2003! Regards, Stacy.

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Re: Re: Re: Re: Unpack for VMS binary files
by pfaut (Priest) on Feb 23, 2003 at 22:56 UTC

    Elian's code wants to do the unpacking. Try something like this. 

    @vals = unpack("x8 v12",$buf);
$timelow = substr($buf,0,4);
$timehigh = substr($buf,4,4);

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    @vals will contain all the short values. This unpack will skip the first eight bytes (the time field) so the time is no longer returned. Instead, the time is pulled out of the buffer in packed form with substr. You can then pass $timelow and $timehigh to Elian's conversion function.

    ---
print map { my ($m)=1<<hex($_)&11?' ':'';
$m.=substr('AHJPacehklnorstu',hex($_),1) }
split //,'2fde0abe76c36c914586c';

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      Yep, your solution works except the time string (in my case) is 32 bytes. Therefore: 
      $timelow = substr($record,0,16);
$timehigh = substr($record,16,32);
&quad_to_epoch("$timelow $timehigh");

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      However,when I print the $Unix_based_time value with print scalar localtime($Unix_based_time), the output starts at 1st Jan 2003 11:00:00 to 23:59:40 and then 2nd Jan 00:00:00 to 10:59:40! The file should start at 00:00:00 Jan 1st and end at 23:59:40 on the same day... Regards, Stacy.
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        The time string can't be 32 bytes. VMS times are quadwords, 64 bit quantites. (Well, 63 bits, since negative times are deltas, but that's a separate issue) The data record format posted in the original node shows it as an 8 byte quantity and if it's in VMS format already, just snag the first eight bytes from the string an throw it in.

        Regardless, as I said before, the code you've posted is wrong. (Which is a separate issue) You can't just go throwing a space between the two variables, nor can you just throw them together and hope for the best when a sub is going to decode the data, especially if it's binary data.. Won't work. The subroutine as written takes a single 64 bit quantity encoded as a VMS quadword time, so if that isn't what you have, you'll have problems. The code you wrote there definitely won't do it.

        Given the original format, just read in the record and pass it to the subroutine, and it should work fine. If you don't want to do that, then: 

           $unix_time = quad_to_epoch(substr($record, 0, 8));

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        will.
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