php - 对于 PHP，如果创建新数组或向现有数组添加相同索引，内存使用情况是否存在显着差异？

Question

如果我要创建一个包含数百个索引的数组，与向现有数组添加第二个维度相比，额外数组需要多少开销？

即$pages['page']['url'] 和 $titles['page']['title'] 对比 $pages['page']['url']['title'] 对比 $pages['page' ]['title']，最后一个示例假设 $pages 的每个索引都包含一个关联数组。

目标是能够查找每个“页面”的两个属性。每个“页面”都有一个“url”和一个“标题”，这对于数组上的内存使用效率会更高吗？哪个用于访问/存储数据？

两个关联数组:

// Store the information in arrays
$titles['page1'] = 'Page 1 Title';
$titles['page2'] = 'Page 2 Title';

$urls['page1'] = 'http://www.page1.com';
$urls['page2'] = 'http://www.page2.com';

// Display an example
echo $titles['page1'] . ' is at ' . $urls['page1']; 

或一组数组:

$pages['page1'] = array( 'title' => 'Page 1 Title', 'url' => 'http://www.page1.com' );
$pages['page2'] = array( 'title' => 'Page 2 Title', 'url' => 'http://www.page2.com' );

// Display an example
echo $pages['page1']['title'] . ' is at ' . $pages['page1']['url'];

Answer 1

二维数组的内存使用量稍大，但这可能是代码错误(？)导致的。

<!--
    http://php.net/manual/en/function.memory-get-usage.php

    array1: 116408 (1D 1001 keys)     (1x 100.000 keys:  11.724.512)
    array2: 116552 (2D, 1002 keys)    (2x  50.000 keys:  11.724.768)

    total:    +144                                             +256
-->

<?php

function genRandomString() {
    $length = 10;
    $characters = '0123456789abcdefghijklmnopqrstuvwxyz';
    $string = '';    

    for ($p = 0; $p < $length; $p++) {
        $string .= $characters[mt_rand(0, strlen($characters))];
    }

    return $string;
}

$i = 0;

// ----- Larger 1D array -----
$mem_start = memory_get_usage();
echo "initial1: " . $mem_start . "<br />";
$arr = array();

for ($i = 1; $i <= 1000; $i++) {
    $arr[ genRandomString() ] = "Hello world!";
}

echo "array1: " . (memory_get_usage() - $mem_start) . "<br />";
unset($arr);

// ----- 2D array -----
$mem_start = memory_get_usage();
$arr2 = array();

echo "initial2: " . $mem_start . "<br />"; 


for ($i = 1; $i <= 500; $i++) {
    $arr2["key______1"][ genRandomString() ] = "Hello world!";
    $arr2["key______2"][ genRandomString() ] = "Hello world!";
}

echo "array2: " . (memory_get_usage() - $mem_start) . "<br />";

unset($arr2);

unset($i);
unset($mem_start)    
echo "final: " . memory_get_usage() . "<br />"; 

?>