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.

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.

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.