First of all, thanks again. I really appreciate the help from all you guys. I also appreciate how much more there is to know about this wonderful language.

A few question re. BrowserUk's code:

1. When I run your code with passing -O=6, for example, it also prints the structure to the screen. This does not happen when omitting the -O=... . Why is that?

2. What is the meaning of pp here? I read in CPAN that it is used to create standalone executables, but I don't understand the connection (and moreover, why do we pass the structure to it...).

3. Can you explain the heart of the packing:

we we print each array to the output file. what does the / between the V and A stand for? I can read it means for a count of the packed items, but where does it value come from? and why do we need the second pack?

And one last question for now - when the ds becomes too large to store it all in memory, is tying with MLDBM the preferred paradigm? What are the alternatives?

Thank you!

1. 1. When I run your code with passing -O=6, for example, it also prints the structure to the screen.

   It should only dump the structure to the screen if -O=2 or less? See the lines that end in if $O <= 2;. There is something wrong with your copy of the code if this is not the case?

   I added that so that I could quickly check that what got unpacked was the same as what was packed. For small examples only.

2. What is the meaning of pp here?

   If you look a the third line of code you'll see: use Data::Dump qw[ pp ];; pp in this case stands for "pretty print" and is Data::Dump's equivalent of Data::Dumper's Dumper() function.

3. Can you explain the heart of the packing:  printf O "%s", pack 'V/A*', pack 'V*', @{ $AoA[ $_ ] };;

   Okay. First off update your copy of the code from the original node where I've switched it from printf to print.

   The guts of the thing is two calls to pack.

   • pack 'V*', @{ $AoA[ $_ ] };

     It goes through the array: @AoA (with $_ set to 0 .. $#AoA) one element at a time getting the reference to the sub-array.

     The @{ ... } bit expands the array reference to the contents of that sub-array.

     The pack format "V*" say pack all the values in the list (produced above), as unsigned integers into a binary string and return that string.

   • pack 'V/A*', ...

     The second pack template "V/A*", says return the input binary string ("A*") prefixed ('/') with a 32-bit unsigned integer ('V').

     And the print writes that out to the file.

   As your sub-arrays are variable sized, we need the prefix count so that we know how much of the file to read back into each sub-array when retrieving it.

   Note: You might prefer to use 'N' rather than 'V' if that is more natural on your platform.

---

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Thanks again. One last question for now (I guess I added it to the previous post while you were replying) : when the ds becomes too large to store it all in memory, is tying with MLDBM the preferred paradigm? What are the alternatives?