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Re^2: Reading huge file content

by kyle (Abbot)
on Dec 06, 2007 at 16:38 UTC ( #655452=note: print w/replies, xml ) Need Help??

in reply to Re: Reading huge file content
in thread Reading huge file content

(perl subs use call-by-value, which makes a copy)

I don't think this is true.

report_mem( 'program start' ); my $big = 'x' x 100_000_000; report_mem( 'after making big string' ); take_big_arg( $big ); sub take_big_arg { printf "got %d characters\n", length $_[0]; report_mem( 'passed to function' ); } sub report_mem { my ( $msg ) = @_; printf "%d %s\n", my_mem(), $msg; } sub my_mem { my ($proc_info) = grep { $_->[2] == $$ } map { [ split ] } `ps l | tail -n +2` +; return $proc_info->[6]; } __END__ 13124 program start 208444 after making big string got 100000000 characters 208444 passed to function

The truth is Perl gives the sub aliases to the variables you pass. Common practice is to copy them after that (my ($copy) = @_), but that's something else.

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Re^3: Reading huge file content
by moritz (Cardinal) on Dec 06, 2007 at 16:55 UTC
    You are right, I stand corrected. And I'm a bit ashamed that I don't know such things after more than a year perl programming and half a year in the monestary..

    In the general case I wouldn't count on the fact that a subroutine doesn't copy one of its arguments, though.

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