in reply to Re^2: How to read number of block in binary files?
in thread How to read number of block in binary files?

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.

Replies are listed 'Best First'.
Re^4: How to read number of block in binary files?
by bh_perl (Monk) on Mar 10, 2009 at 02:31 UTC

    Hi.. Thank for your info.. that very helpful.. But could you guide me how could i read the binary files until end of file ?..

    This is my latest code:- 

    if ($fname) {
        open (OUTPUT, ">$fname.tmp") or die "Can't open $fname.tmp $!\
+n";
        open (DATA, "<$fname") or die "Can't open $fname $!\n";
        binmode DATA;

        read(DATA, $data, BLOCKHDR);
        $blockhdr = unpack "H*", $data;

        read(DATA, $data, BLOCKDATA);
        $blockdt  = unpack "H*", $data;

        my $t_cdr = hextoint(reverse_str(substr($blockdt,4)));
        my $blocklen = $t_cdr * 286;

        read(DATA, $data, $blocklen);
        my $record = unpack "H*", $data;

        close(DATA);
        close(OUTPUT);
} else {

    [download]
[reply]
[d/l]

      This is UNTESTED but you may want code something like this:

      Update to while loop conditional. 

      use constant HEADER_LEN => 32;
use constant RECORD_LEN => 286;
use constant DUMMY      => "\0" x RECORD_LEN;

if ( $fname ) {

    open my $OUTPUT, '>:raw', "$fname.tmp" or die "Cannot open '$fname
+.tmp' $!";
    open my $INPUT,  '<:raw', $fname       or die "Cannot open '$fname
+' $!";

RECORD:
    {
        my ( $offset, $bytes_read, $header ) = ( 0, 0, '' );
#        while ( $bytes_read < HEADER_LEN ) {
        while ( $offset < HEADER_LEN ) {
            defined( $bytes_read = read $INPUT, $header, HEADER_LEN - 
+$offset, $offset )
                or die "Cannot read from '$fname' $!";
            $bytes_read or last RECORD;  # EOF
            $offset += $bytes_read;
            }

        # format may be either 'x30 n' or 'x30 S' depending on endiane
+ss?
        my $total_record = unpack 'x30 n', $header;

        my $records_len = $total_record * RECORD_LEN;

        ( $offset, $bytes_read, my $data ) = ( 0, 0, '' );
#        while ( $bytes_read < $records_len ) {
        while ( $offset < $records_len ) {
            defined( $bytes_read = read $INPUT, $data, $records_len - 
+$offset, $offset )
                or die "Cannot read from '$fname' $!";
            $bytes_read or last RECORD;  # EOF
            $offset += $bytes_read;
            }

        $header = pack 'a30 n', $header, 3;

        print $OUTPUT $header, $data, $total_record == 2 ? DUMMY : '';
        redo;
        }

    }

      [download]
[reply]
[d/l]

In Section Seekers of Perl Wisdom