Jeroen Lodewijks wrote:
>
> Hi all,
Hello,
> I have a 2 questions about the internal representation of a hash or array.
> Consider this piece of code:
>
> 1)
>
> sub PassHash
> {
> my (%hash) = @_;
>
> $hash{$some_key} = 'test';
> ...
> }
>
> PassHash(%hash);
>
> What happens internally?
perldoc perlsub
> Will the whole contents of the hash be copied in memory?
Yes, the statement "my (%hash) = @_;" copies the list passed to
PassHash() into the hash %hash.
> Or is only a reference passed?
If you use the contents of @_ directly then you are dealing with
references to the original variables.
> Will the $some_key element show up after PassHash?
Yes.
> Does the same apply to arrays?
Yes.
> 2)
>
> sub CreatHash
> {
> my %hash;
>
> ... do something with hash;
>
> return %hash;
> }
>
> sub OtherProc
> {
> my %new_hash = CreateHash();
>
> ....
> }
>
> What happens internally?
perldoc perlsub
> Will the whole contents of the hash be copied in memory to %new_hash?
The whole contents of %hash will be flattened to a list in memory and
the list will be copied to %new_hash.
> Or is only a reference passed?
No.
> When is %hash garbage collected and when is %new_hash?
When they go out of scope at the end of the subs they are in.
> Does the same apply to arrays?
Yes.
> Thank you for you answers in advance. I need this information to
> optimise memory requirements for my program.
perldoc -q "How can I make my Perl program run faster"
perldoc -q "How can I make my Perl program take less memory"
And if you are really brave search for 'memory' in perldebguts.pod
perldoc perldebguts
John
--
use Perl;
program
fulfillment
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