• 引用计数refcount和is_ref,也就是php不会随意的malloc内存空间,而是用类似c的指针的方式,增加引用计数,引用计数为0就free掉变量,每个变量在底层实现都是一个在zval的结构体
• php5.3之前无法解决循环引用计数的问题,会导致内存泄漏.php5.3以后,采用深度优先遍历解决了这个问题,具体实现细节我也不清楚

<?php

/**

 * 用class模拟struct,实现链表节点定义

 */

class Node

{

    /**

     * 数据

     */

    public $data;

    /**

     * 下一个节点

     */

    public $next;

    public function __construct ($data, $next = null)

    {

        $this->data = $data;

        $this->next = $next;

    }

}

class LinkList

{

    public $head;

    public function __construct ()

    {

        $this->head = null;

    }

    /**

     * 尾插法实现链表插入操作

     *

     * @param int $value

     */

    public function insertNode ($value)

    {

        $cur = $this->head;

        $pre = null;

        while ($cur != null) {

            $pre = $cur;

            $cur = $cur->next;

        }

        $new = new Node($value);

        $new->next = null;

        if ($pre == null) {

            $this->head = $new;

        } else {

            $pre->next = $new;

        }

    }

    /**

     * 单链表中删除指定节点

     *

     * @param int $value

     */

    public function deleteNode ($value)

    {

        $cur = $this->head;

        $pre = null;

        while ($cur != null) {

            if ($cur->data == $value) {

                if ($pre == null) {

                    $this->head->next = $cur->next;

                } else {

                    $pre->next = $cur->next;

                }

                break;

            }

            $pre = $cur;

            $cur = $cur->next;

        }

    }

    /**

     * 打印单链表

     */

    public function printList ()

    {

        $cur = $this->head;

        while ($cur->next != null) {

            printf("%d ", $cur->data);

            $cur = $cur->next;

        }

        printf("%d\n", $cur->data);

    }

}

// 测试

$list = new LinkList();

$list->insertNode(1);

$list->insertNode(2);

$list->insertNode(3);

$list->insertNode(4);

$list->insertNode(5);

$list->insertNode(6);

$list->printList();

$list->deleteNode(4);

$list->printList();

PHP实现字符串反转

<?php

function strReverse(&$str)

{

    for ($i = 0, $j = strlen($str); $i <= $j; $i ++, $j --) {

        $tmp = $str[$i];

        $str[$i] = $str[$j];

        $str[$j] = $tmp;

    }

}

$str = "wangzhengyi";

strReverse($str);

echo $str;

PHP变量的内部实现