This is one example where references actually decrease memory usage.
The main reason is the recursive nature of the function. Try
<?php
echo memory_get_usage() . PHP_EOL;
$array = range(0,1000000);
$array[10] = range(0,10);
$array[20] = range(0,10);
$array[30] = range(0,10);
$array[40] = range(0,10);
$array[50] = range(0,10);
$array[60] = range(0,10);
$array[70] = range(0,10);
$array[80] = range(0,10);
$array[90] = range(0,10);
$array[100] = range(0,10);
echo memory_get_usage() . PHP_EOL;
carray($array);
function carray ($array)
{
foreach ($array as $value)
{
if (is_array($value)) carray($value);
}
echo memory_get_usage() . PHP_EOL;
echo count($array) . PHP_EOL;
}
echo memory_get_usage() . PHP_EOL;
And then compare with:
<?php
echo memory_get_usage() . PHP_EOL;
$array = range(0,1000000);
$array[10] = range(0,10);
$array[20] = range(0,10);
$array[30] = range(0,10);
$array[40] = range(0,10);
$array[50] = range(0,10);
$array[60] = range(0,10);
$array[70] = range(0,10);
$array[80] = range(0,10);
$array[90] = range(0,10);
$array[100] = range(0,10);
echo memory_get_usage() . PHP_EOL;
carray($array);
function carray (&$array)
{
$i = 0;
foreach ($array as $value)
{
if (is_array($value)) carray($value);
}
echo memory_get_usage() . PHP_EOL;
echo count($array) . PHP_EOL;
}
echo memory_get_usage() . PHP_EOL;
The memory usage spikes in the first example when you hit the second
array level - you don't see the same spike in the second example.
Regards
Peter
On 16 March 2010 15:46, Robert Cummings <robert@xxxxxxxxxxxxx> wrote:
>
>
> Richard Quadling wrote:
>>
>> On 15 March 2010 23:45, Daevid Vincent <daevid@xxxxxxxxxx> wrote:
>>>
>>> Anyone have a function that will return an integer of the number of
>>> dimensions an array has?
>>
>> /**
>> * Get the maximum depth of an array
>> *
>> * @param array &$Data A reference to the data array
>> * @return int The maximum number of levels in the array.
>> */
>> function arrayGetDepth(array &$Data) {
>> static $CurrentDepth = 1;
>> static $MaxDepth = 1;
>>
>> array_walk($Data, function($Value, $Key) use(&$CurrentDepth,
>> &$MaxDepth) {
>> if (is_array($Value)) {
>> $MaxDepth = max($MaxDepth, ++$CurrentDepth);
>> arrayGetDepth($Value);
>> --$CurrentDepth;
>> }
>> });
>>
>> return $MaxDepth;
>> }
>>
>> Extending Jim and Roberts comments to this. No globals. By using a
>> reference to the array, large arrays are not copied (memory footprint
>> is smaller).
>
> Using a reference actually increases overhead. References in PHP were mostly
> useful in PHP4 when assigning objects would cause the object to be copied.
> But even then, for arrays, a Copy on Write (COW) strategy was used (and is
> still used) such that you don't copy any values. Try it for yourself:
>
> <?php
>
> $copies = array();
> $string = str_repeat( '*', 1000000 );
>
> echo memory_get_usage()."\n";
> for( $i = 0; $i < 1000; $i++ )
> {
> $copies[] = $string;
> }
> echo memory_get_usage()."\n";
>
> ?>
>
> Cheers,
> Rob.
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> http://www.interjinn.com
> Application and Templating Framework for PHP
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