php 查看数组占用的内存大小

<?php

function convert($size)
{
$unit=array('b','kb','mb','gb','tb','pb');
return @round($size/pow(1024,($i=floor(log($size,1024)))),2).' '.$unit[$i];
}

$start = memory_get_usage();
//$a = array_fill(0, 10000, 1);
$a = [];
$b = [];
for ($i=0; $i<10000;$i++){
$a[] = 'chenghuan';
}
$mid = memory_get_usage(true); //10k elements array;
echo 'argv:', convert($mid) , '<br>';
for ($j=0; $j<10000;$j++){
$a[] = 'chenghuan';
}
$end = memory_get_usage(true); //10k elements array;
echo 'argv:',  convert($end)  , '<br>';