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Binary Files...

yapp
User

Aug 29, 2001, 3:43 AM

Post #1 of 5 (2076 views)

Binary Files...	Can't Post

Hi There.

I've got a prop with making binary-type-files in perl. Normally I use text files to save my data, but this time Iwant to try using a binary structure (using pack and unpack?) Who knows howto make that?
I hope it's possible to make something like first byte=number, then variable length string, etc.

mhx
Enthusiast / Moderator

Aug 29, 2001, 4:36 AM

Post #2 of 5 (2072 views)

Re: Binary Files... [In reply to]	Can't Post

First, you need to be sure your file handle is set to binary mode. See perldoc -f binmode for details on this.
Second, the functions you're searching for are pack and unpack. You will find detailed information on these functions with perldoc -f pack and perldoc -f unpack.
Hope this helps.

-- Marcus

Code

s$$ab21b8d15c3d97bd6317286d$;$"=547269736;split'i',join$,,map{chr(($*+= 
($">>=1)&1?-hex:hex)+0140)}/./g;$"=chr$";s;.;\u$&;for@_[0,2];print"@_,"

yapp
User

Aug 30, 2001, 5:30 AM

Post #3 of 5 (2064 views)

Re: Binary Files... [In reply to]	Can't Post

That you for your advice, but unfortunatuly I already knew that. I read thu the perldoc. I need binmode() on some systems, but I don't get pack() and unpack()!

What kind of template/formula should I use when I want to save a number, variable length string, numbers and so on? Especially the variable length is the proplem.

Anyway, who userstands such things?

mhx
Enthusiast / Moderator

Aug 30, 2001, 9:52 AM

Post #4 of 5 (2062 views)

Re: Binary Files... [In reply to]	Can't Post

Say you've got two strings $s1 and $s2, then you can use for example:

Code

#!/bin/perl -w 
use strict; 
  
my $s1 = 'foo bar'; 
my $s2 = 'Hello World'; 
  
my $bin = pack 'na*na*', length $s1, $s1, 
                         length $s2, $s2; 
  
# now do something with $bin 
  
my($u1,$u2) = unpack 'n/an/a', $bin; 
  
print "[$u1]\n[$u2]\n";

This will work for strings of up to 65535 characters. 'n' is always a big endian unsigned 2-byte integer.
Hope this helps.

-- Marcus

Code

s$$ab21b8d15c3d97bd6317286d$;$"=547269736;split'i',join$,,map{chr(($*+= 
($">>=1)&1?-hex:hex)+0140)}/./g;$"=chr$";s;.;\u$&;for@_[0,2];print"@_,"

yapp
User

Sep 4, 2001, 2:23 AM

Post #5 of 5 (2051 views)

Re: Binary Files... [In reply to]	Can't Post

That leaves me still with one question. I hope someone can answer it. How do I store 100 strings efficiently in a file?

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