Re: Iteratively unpack structure from binary file

I would say that the first step is to find the length in bytes of the raw data block represented by 'i i f f f' (remembering that the data sizes of these template specifiers are implementation dependent).

c:\@Work\Perl>perl -wMstrict -le
"my $template = 'i2 f3';
 ;;
 sub template_len {
   my ($template) = @_;
   ;;
   my $s = pack $template;
   return length $s;
   }
 ;;
 my $buf_size = template_len($template);
 print $buf_size;
 ;;
 print template_len('i i f f f');
 print template_len('i f3 i');
"
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Knowing the size of a single raw block allows reading n raw blocks of data at a time with, IIRC, read or sysread (or the appropriate buffered-read built-in) and then unpack-ing with a template like "($template)n" or just "($template)*".

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Re^2: Iteratively unpack structure from binary file by ikegami (Patriarch) on Oct 20, 2014 at 18:33 UTC
Well, `read` buffers, so, `my $template = 'iifff'; my $rec_size = template_len($template); while (1) { my $rv = read($fh, my $rec, $rec_size); die "$!\n" if !defined($rv); last if !$rv; die "Premature EOF\n" if $rv < $rec_size; my @fields = unpack($template, $rec); ... }` [download]	[reply] [d/l] [select]

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Re^2: Iteratively unpack structure from binary file
by ikegami (Patriarch) on Oct 20, 2014 at 18:33 UTC

read

my $template = 'iifff';
my $rec_size = template_len($template);
while (1) {
   my $rv = read($fh, my $rec, $rec_size);
   die "$!\n" if !defined($rv);
   last if !$rv;
   die "Premature EOF\n" if $rv < $rec_size;

   my @fields = unpack($template, $rec);
   ...
}
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