Hi monks, I'm new to the board and I've been struggling with this problem for some time now. Hope someone can give me some suggestions... I am trying to read a binary file with the following format: The 4-byte integer and (4 byte float) are in the native format of the machine. 
*** First record
(4 byte integer) - byte size of record (4*N) (f77 header)
(4 byte float) .. value 1
(4 byte float) .. value 2
...
(4 byte float) .. value N N = number of grid points in the field
(4 byte integer) .. byte size of record (4*N) (f77 trailer)

**** Second record
(4 byte integer) - byte size of record (4*N) (f77 header)
(4 byte float) .. value 1
(4 byte float) .. value 2
...
(4 byte float) .. value N N = number of grid points in the field
(4 byte integer) .. byte size of record (4*N) (f77 trailer)

[download]
The data is meteorological data (temperature in degrees K) on a 614 x 428 grid. I tried coding up a reader for this, but am getting nonsensical results. Here is the code: 
my $out_file = "/dicast2-papp/DICAST/smg_data/" . $gfn . ".bin"; #path
+ to binary file
my $template = "if262792i"; #binary layout (integer 262792 floats   in
+teger) as described in the format documentation above (not sure if th
+is is correct)
my $record_length = 4; #not sure what record_length is supposed to rep
+resent (number of values in 1st record, or should it be length of var
+iable [4 bytes]) 
my (@fields,$record);
open (FH, $out_files ) || die  "couldn't open $out_files\n";
until (eof(FH))
{
    my $val_of_read = read (FH, $record, $record_length) ==   $record_
+length
            or die "short read\n";
   @fields = unpack ($template, $record);
   print "field = $fields[0]\n";
}

[download]
The results I get when I print out the first field are non-sensical (negative numbers, etc). I think the issue is that I'm not properly setting up my template and record length. Also, how do I find out what is "the native format of the machine"?

In reply to reading binary files with Perl by jpk1292000

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.