深入理解PHP之数组(遍历顺序)

• 作者: Laruence(   )
• 本文地址: http://www.laruence.com/2009/08/23/1065.html
• 转载请注明出处

经常会有人问我, PHP的数组, 如果用foreach来访问, 遍历的顺序是固定的么? 以什么顺序遍历呢?
比如:

<ol style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; list-style-type: none;"><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><?php</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_variable" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(198, 197, 254);">$arr</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">[</span><span class="sh_string" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(168, 255, 96);">'laruence'</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">]</span> <span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">=</span> <span class="sh_string" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(168, 255, 96);">'huixinchen'</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">;</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_variable" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(198, 197, 254);">$arr</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">[</span><span class="sh_string" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(168, 255, 96);">'yahoo'</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">]</span>    <span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">=</span> <span class="sh_number" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(255, 115, 253);">2007</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">;</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_variable" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(198, 197, 254);">$arr</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">[</span><span class="sh_string" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(168, 255, 96);">'baidu'</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">]</span>    <span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">=</span> <span class="sh_number" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(255, 115, 253);">2008</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">;</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_keyword" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(150, 203, 254);">foreach</span> <span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">(</span><span class="sh_variable" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(198, 197, 254);">$arr</span> <span class="sh_keyword" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(150, 203, 254);">as</span> <span class="sh_variable" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(198, 197, 254);">$key</span> <span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">=></span> <span class="sh_variable" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(198, 197, 254);">$val</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">)</span> <span class="sh_cbracket" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">{</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_comment" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(124, 124, 124);">//结果是什么?</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_cbracket" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">}</span></li></ol>

又比如:

<ol style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; list-style-type: none;"><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><?php</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_variable" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(198, 197, 254);">$arr</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">[</span><span class="sh_number" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(255, 115, 253);">2</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">]</span> <span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">=</span> <span class="sh_string" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(168, 255, 96);">'huixinchen'</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">;</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_variable" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(198, 197, 254);">$arr</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">[</span><span class="sh_number" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(255, 115, 253);">1</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">]</span>  <span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">=</span> <span class="sh_number" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(255, 115, 253);">2007</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">;</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_variable" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(198, 197, 254);">$arr</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">[</span><span class="sh_number" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(255, 115, 253);">0</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">]</span>  <span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">=</span> <span class="sh_number" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(255, 115, 253);">2008</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">;</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_keyword" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(150, 203, 254);">foreach</span> <span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">(</span><span class="sh_variable" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(198, 197, 254);">$arr</span> <span class="sh_keyword" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(150, 203, 254);">as</span> <span class="sh_variable" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(198, 197, 254);">$key</span> <span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">=></span> <span class="sh_variable" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(198, 197, 254);">$val</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">)</span> <span class="sh_cbracket" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">{</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_comment" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(124, 124, 124);">//现在结果又是什么?</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_cbracket" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">}</span></li></ol>

要完全了解清楚这个问题, 我想首先应该要大家了解PHP数组的内部实现结构………

PHP的数组

在PHP中, 数组是用一种HASH结构(HashTable)来实现的, PHP使用了一些机制, 使得可以在O(1)的时间复杂度下实现数组的增删, 并同时支持线性遍历和随机访问.

之前的文章中也讨论过, PHP的HASH算法, 基于此, 我们做进一步的延伸.

认识HashTable之前, 首先让我们看看HashTable的结构定义, 我加了注释方便大家理解:

<ol style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; list-style-type: none;"><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_keyword" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(150, 203, 254);">typedef</span> <span class="sh_keyword" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(150, 203, 254);">struct</span><span class="sh_normal" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"> </span><span class="sh_classname" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">_hashtable</span> <span class="sh_cbracket" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">{</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_usertype" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">uint</span><span class="sh_normal" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"> </span>nTableSize<span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">;</span>        <span class="sh_comment" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(124, 124, 124);">/* 散列表大小, Hash值的区间 */</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_usertype" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">uint</span><span class="sh_normal" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"> </span>nTableMask<span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">;</span>        <span class="sh_comment" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(124, 124, 124);">/* 等于nTableSize -1, 用于快速定位 */</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_usertype" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">uint</span><span class="sh_normal" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"> </span>nNumOfElements<span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">;</span>    <span class="sh_comment" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(124, 124, 124);">/* HashTable中实际元素的个数 */</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_usertype" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">ulong</span><span class="sh_normal" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"> </span>nNextFreeElement<span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">;</span> <span class="sh_comment" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(124, 124, 124);">/* 下个空闲可用位置的数字索引 */</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_usertype" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">Bucket</span><span class="sh_normal" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"> </span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">*</span>pInternalPointer<span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">;</span>   <span class="sh_comment" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(124, 124, 124);">/* 内部位置指针, 会被reset, current这些遍历函数使用 */</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_usertype" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">Bucket</span><span class="sh_normal" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"> </span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">*</span>pListHead<span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">;</span>      <span class="sh_comment" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(124, 124, 124);">/* 头元素, 用于线性遍历 */</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_usertype" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">Bucket</span><span class="sh_normal" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"> </span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">*</span>pListTail<span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">;</span>      <span class="sh_comment" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(124, 124, 124);">/* 尾元素, 用于线性遍历 */</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_usertype" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">Bucket</span><span class="sh_normal" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"> </span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">**</span>arBuckets<span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">;</span>     <span class="sh_comment" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(124, 124, 124);">/* 实际的存储容器 */</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_usertype" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">dtor_func_t</span><span class="sh_normal" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"> </span>pDestructor<span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">;</span><span class="sh_comment" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(124, 124, 124);">/* 元素的析构函数(指针) */</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_usertype" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">zend_bool</span><span class="sh_normal" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"> </span>persistent<span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">;</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_type" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(255, 255, 182);">unsigned</span> <span class="sh_type" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(255, 255, 182);">char</span> nApplyCount<span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">;</span> <span class="sh_comment" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(124, 124, 124);">/* 循环遍历保护 */</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_usertype" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">zend_bool</span><span class="sh_normal" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"> </span>bApplyProtection<span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">;</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_preproc" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(255, 210, 167);">#if</span> ZEND_DEBUG</li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_type" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(255, 255, 182);">int</span> inconsistent<span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">;</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_preproc" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(255, 210, 167);">#endif</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_cbracket" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">}</span> HashTable<span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">;</span></li></ol>

关于nApplyCount的意义, 我们可以通过一个例子来了解:

<ol style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; list-style-type: none;"><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><?php</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">    <span class="sh_variable" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(198, 197, 254);">$arr</span> <span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">=</span> <span class="sh_keyword" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(150, 203, 254);">array</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">(</span><span class="sh_number" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(255, 115, 253);">1</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">,</span><span class="sh_number" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(255, 115, 253);">2</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">,</span><span class="sh_number" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(255, 115, 253);">3</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">,</span><span class="sh_number" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(255, 115, 253);">4</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">,</span><span class="sh_number" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(255, 115, 253);">5</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">,);</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">    <span class="sh_variable" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(198, 197, 254);">$arr</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">[]</span> <span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">=</span> <span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">&</span><span class="sh_variable" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(198, 197, 254);">$arr</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">;</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"> </li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">    <span class="sh_function" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(255, 210, 167);">var_export</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">(</span><span class="sh_variable" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(198, 197, 254);">$arr</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">);</span> <span class="sh_comment" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(124, 124, 124);">//Fatal error: Nesting level too deep - recursive dependency?</span></li></ol>

这个字段就是为了防治循环引用导致的无限循环而设立的.

查看上面的结构, 可以看出, 对于HashTable, 关键元素就是arBuckets了, 这个是实际存储的容器, 让我们来看看它的结构定义:

<ol style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; list-style-type: none;"><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_keyword" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(150, 203, 254);">typedef</span> <span class="sh_keyword" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(150, 203, 254);">struct</span><span class="sh_normal" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"> </span><span class="sh_classname" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">bucket</span> <span class="sh_cbracket" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">{</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_usertype" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">ulong</span><span class="sh_normal" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"> </span>h<span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">;</span>                        <span class="sh_comment" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(124, 124, 124);">/* 数字索引/hash值 */</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_usertype" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">uint</span><span class="sh_normal" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"> </span>nKeyLength<span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">;</span>                <span class="sh_comment" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(124, 124, 124);">/* 字符索引的长度 */</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_type" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(255, 255, 182);">void</span> <span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">*</span>pData<span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">;</span>                    <span class="sh_comment" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(124, 124, 124);">/* 数据 */</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_type" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(255, 255, 182);">void</span> <span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">*</span>pDataPtr<span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">;</span>                 <span class="sh_comment" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(124, 124, 124);">/* 数据指针 */</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_keyword" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(150, 203, 254);">struct</span><span class="sh_normal" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"> </span><span class="sh_classname" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">bucket</span> <span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">*</span>pListNext<span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">;</span>               <span class="sh_comment" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(124, 124, 124);">/* 下一个元素, 用于线性遍历 */</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_keyword" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(150, 203, 254);">struct</span><span class="sh_normal" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"> </span><span class="sh_classname" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">bucket</span> <span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">*</span>pListLast<span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">;</span>       <span class="sh_comment" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(124, 124, 124);">/* 上一个元素, 用于线性遍历 */</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_keyword" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(150, 203, 254);">struct</span><span class="sh_normal" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"> </span><span class="sh_classname" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">bucket</span> <span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">*</span>pNext<span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">;</span>                   <span class="sh_comment" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(124, 124, 124);">/* 处于同一个拉链中的下一个元素 */</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_keyword" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(150, 203, 254);">struct</span><span class="sh_normal" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"> </span><span class="sh_classname" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">bucket</span> <span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">*</span>pLast<span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">;</span>                   <span class="sh_comment" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(124, 124, 124);">/* 处于同一拉链中的上一个元素 */</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_type" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(255, 255, 182);">char</span> arKey<span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">[</span><span class="sh_number" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(255, 115, 253);">1</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">];</span> <span class="sh_comment" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(124, 124, 124);">/* 节省内存,方便初始化的技巧 */</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_cbracket" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">}</span> Bucket<span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">;</span></li></ol>

我们注意到, 最后一个元素, 这个是flexible array技巧, 可以节省内存,和方便初始化的一种做法, 有兴趣的朋友可以google flexible array.

h是元素的Hash值,对于数字索引的元素,h为直接索引值(通过nKeyLength=0来表示是数字索引).而对于字符串索引来说, 索引值保存在arKey中, 索引的长度保存在nKeyLength中.

在Bucket中，实际的数据是保存在pData指针指向的内存块中，通常这个内存块是系统另外分配的。但有一种情况例外，就是当Bucket保存 的数据是一个指针时，HashTable将不会另外请求系统分配空间来保存这个指针，而是直接将该指针保存到pDataPtr中，然后再将pData指向本结构成员的地址。这样可以提高效率，减少内存碎片。由此我们可以看到PHP HashTable设计的精妙之处。如果Bucket中的数据不是一个指针，pDataPtr为NULL(本段来自Altair的”Zend HashTable详解”)

结合上面的HashTable结构, 我们来说明下HashTable的总结构图:

HashTable结构示意图

HashTable的pListhHead指向线性列表形式下的第一个元素, 上图中是元素1, pListTail指向的是最后一个元素0, 而对于每一个元素pListNext就是红色线条画出的线性结构的下一个元素, 而pListLast是上一个元素.

pInternalPointer指向当前的内部指针的位置, 在对数组进行顺序遍历的时候, 这个指针指明了当前的元素.

当在线性(顺序)遍历的时候, 就会从pListHead开始, 顺着Bucket中的pListNext/pListLast, 根据移动pInternalPointer, 来实现对所有元素的线性遍历.

比如, 对于foreach, 如果我们查看它生成的opcode序列, 我们可以发现, 在foreach之前, 会首先有个FE_RESET来重置数组的内部指针, 也就是pInternalPointer(关于foreach可以参看深入理解PHP原理之foreach), 然后通过每次FE_FETCH来递增pInternalPointer,从而实现顺序遍历.

类似的, 当我们使用, each/next系列函数来遍历的时候, 也是通过移动数组的内部指针而实现了顺序遍历, 这里有一个问题, 比如:

<ol style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; list-style-type: none;"><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><?php</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_variable" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(198, 197, 254);">$arr</span> <span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">=</span> <span class="sh_keyword" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(150, 203, 254);">array</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">(</span><span class="sh_number" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(255, 115, 253);">1</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">,</span><span class="sh_number" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(255, 115, 253);">2</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">,</span><span class="sh_number" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(255, 115, 253);">3</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">,</span><span class="sh_number" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(255, 115, 253);">4</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">,</span><span class="sh_number" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(255, 115, 253);">5</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">);</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_keyword" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(150, 203, 254);">foreach</span> <span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">(</span><span class="sh_variable" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(198, 197, 254);">$arr</span> <span class="sh_keyword" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(150, 203, 254);">as</span> <span class="sh_variable" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(198, 197, 254);">$v</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">)</span> <span class="sh_cbracket" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">{</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_comment" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(124, 124, 124);">//可以获取</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_cbracket" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">}</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"> </li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_keyword" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(150, 203, 254);">while</span> <span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">(</span><span class="sh_keyword" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(150, 203, 254);">list</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">(</span><span class="sh_variable" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(198, 197, 254);">$key</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">,</span> <span class="sh_variable" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(198, 197, 254);">$v</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">)</span> <span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">=</span> <span class="sh_keyword" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(150, 203, 254);">each</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">(</span><span class="sh_variable" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(198, 197, 254);">$arr</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">))</span> <span class="sh_cbracket" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">{</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_comment" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(124, 124, 124);">//获取不到</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_cbracket" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">}</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">?></span></li></ol>

了解到我刚才介绍的知识, 那么这个问题也就很明朗了, 因为foreach会自动reset, 而while这块不会reset, 所以在foreach结束以后, pInternalPointer指向数组最末端, while语句块当然访问不到了, 解决的办法就是在each之前, 先reset数组的内部指针.

而在随机访问的时候, 就会通过hash值确定在hash数组中的头指针位置, 然后通过pNext/pLast来找到特点元素.

增加元素的时候, 元素会插在相同Hash元素链的头部和线性列表的尾部. 也就是说, 元素在线性遍历的时候是根据插入的先后顺序来遍历的, 这个特殊的设计使得在PHP中,当使用数字索引时, 元素的先后顺序是由添加的顺序决定的,而不是索引顺序.

也就是说, PHP中遍历数组的顺序, 是和元素的添加先后相关的, 那么, 现在我们就很清楚的知道, 文章开头的问题的输出是:

<ol style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; list-style-type: none;"><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">huixinchen</li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_number" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(255, 115, 253);">2007</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_number" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(255, 115, 253);">2008</span></li></ol>

所以, 如果你想在数字索引的数组中按照索引大小遍历, 那么你就应该使用for, 而不是foreach

<ol style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; list-style-type: none;"><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_keyword" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(150, 203, 254);">for</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">(</span><span class="sh_variable" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(198, 197, 254);">$i</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">=</span><span class="sh_number" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(255, 115, 253);">0</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">,</span><span class="sh_variable" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(198, 197, 254);">$l</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">=</span><span class="sh_function" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(255, 210, 167);">count</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">(</span><span class="sh_variable" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(198, 197, 254);">$arr</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">);</span> <span class="sh_variable" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(198, 197, 254);">$i</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><</span><span class="sh_variable" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(198, 197, 254);">$l</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">;</span> <span class="sh_variable" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(198, 197, 254);">$i</span><span class="sh_symbol" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">++)</span> <span class="sh_cbracket" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">{</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"> <span class="sh_comment" style="margin: 0px; padding: 0px; border: 0px; font-family: inherit; vertical-align: baseline; color: rgb(124, 124, 124);">//这个时候,不能认为是顺序遍历(线性遍历)</span></li><li style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;"><span class="sh_cbracket" style="margin: 0px; padding: 0px; border: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline;">}</span></li></ol>