This is because if the block contain 2 record the length is 604 while 3 record is 890 bytes. So that why i set $offset -= 286. is it correct ?

read( DATA, $data, BLOCKLEN, $offset );

is the same as saying:

read( DATA, my $temp, BLOCKLEN );
substr( $data, $offset ) = $temp;

and then the next statement:

my $blockhdr = unpack "H*", substr($data, 0, BLOCKHDR);

always extracts data from offset 0, at the beginning of $data

You need to read BLOCKHDR + BLOCKDATA data first, extract the $total_record value from that and then read $total_record * 286 data to get the actual records.

In reply to Re^3: How to read number of block in binary files? by jwkrahn
in thread How to read number of block in binary files? by bh_perl

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.