So precreate the string. Doing so doesn't cost a lot (assuming your sample represents your real code) so probably doesn't impact performance much for small numbers of iterations but, as you have discovered, provides a big win for large numbers of iterations.

If you really don't want to do that, you can get most of the benefit by using a piecemeal preallocate and copy technique:

use strict;
use warnings;

#number of items to pack
my $iter = 1000000;
my $string;
my $startAlloc = 0;
my $preAllocSize = $startAlloc;

Time ();
$$string = '';

#now lets create the data block...
for my $count (1 .. $iter) {
    if ($preAllocSize && length ($$string) >= $preAllocSize) {
        $preAllocSize = length ($$string) * 2;
        my $newStr = 1 x $preAllocSize;
        $newStr = $$string;
        $string = \$newStr;
    }

    $$string .= 'x' x 20;
}
Time ();
print "Finished with start alloc: $startAlloc\n";
print "Final string length: ", length ($$string);

sub Time {
    my ($user, $system, $cuser, $csystem) = times;
    print "$user,$system\n";
}

[download]

for two different runs prints:

0.015,0
18.345,29.78
Finished with start alloc: 0
Final string length: 20000000

0.015,0
0.374,0.046
Finished with start alloc: 1
Final string length: 20000000

[download]
True laziness is hard work

In reply to Re: Memory allocation/performance issue for large strings (of binary data) under Windows. by GrandFather
in thread Memory allocation/performance issue for large strings (of binary data) under Windows. by Anonymous Monk

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