in reply to Reading binary file is not accurate ?

BLOCKLEN (1531) = BLOCKHDR(14) + MAXRECORD(9) * CDRLEN(160) + BLOCKTRL(77), but ... 

    # Read Block
    while (read (DATA, $data, BLOCKLEN)) {
        # Read Block Header
        read (DATA, $data, BLOCKHDR);

[download]

You read the whole block into $data and then attempt to read the individual parts, promptly overwriting (and therefore discarding) $data.

You should either:

  1. read the whole block and then extract the header/CDAs/trailer from what you read($data); or
  2. Read the header/CDAs/trailers individually.

Not do both!

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.
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Re^2: Reading binary file is not accurate ?
by bh_perl (Monk) on May 03, 2010 at 03:18 UTC
    Hi..
    Could you give some example..
[reply]

      The first method I described--read the entire block, and then extract the header, records and trailer from it--would look something like this: 

      while( read DATA, $data, BLOCKLEN ) {
    ## Extract the header from the front of the block
    my $header = substr $data, 0, BLOCKHDR, ''; 
    
    ## do stuff with $header
    
    for my $cdr ( 1 .. MAXRECORD ) {
        ## Extract each record in turn from $data
        my $record = substr $data, 0, CDRLEN, '';
        
        ## do stuff with $record
    }
    my $trailer = $data; ## Anything left in $data should be your trai
+ler.
    
    ## do something with it.
}

      [download]

      The second method I described might be done something like this: 

      until( eof DATA ) {
    read DATA, my $header, BLOCKHDR or die;
    ## Do stuff with $header;
    
    for my $cdr ( 1 .. MAXRECORD ) {
        read DATA, my $record, CDRLEN or die;
        ## Do stuff with $record
    }
    
    read DATA, my $trailer, BLOCKTRL or die;
    ## Do stuff with $trailer
}

      [download]
      Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
      "Science is about questioning the status quo. Questioning authority".
      In the absence of evidence, opinion is indistinguishable from prejudice.
[reply]
[d/l]
[select]
        Hi..

        Thank you very much for your help and now my program working properly.
[reply]

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