php高级基础--php在foreach循环后留下数组的引用问题

2019-07-31 21:20:24 12 PHP应用 6763 12 百度已收录

示例:

<?php
    $arr = array(1,2,3,4);
    foreach($arr as $key => &$value){
    }
    foreach($arr as $key => $value){
    }
?>

结果：

[1,2,3,3]

解释:

1. foreach不是块级域，数组引用结束，$key , $value  并没有释放内存
2. 当第一次引用循环结束的时候，$value指向数组最后一个元素4
3. 当第二次开始循环 (此时$value 已经是指向最后一个元素，是引用)
循环4次  数组的变化分别是:
1   ->    [1,2,3,4]
2   ->    [1,2,3,4]
3   ->    [1,2,3,3]

第三次value指向最后一个元素3 但是value是全局引用在上次循环指向了最后一个元素所以value=3的时候也会把最后一个元素的值改为3

4   ->    [1,2,3,3]

注意事项：

1. foreach 实现原理有个内部指针的概念
2. &的foreach循环结束   指针会指向最后一个元素

如何避免：
在用&foreach循环后 unset ($value)

2019-08-01: 今天看到很多人在关注这个问题，关于鸟哥解释的php源码分析的foreach，大家感兴趣的可以去看看：http://www.laruence.com/2008/11/20/630.html

转载：深入理解PHP内存管理之谁动了我的内存

array_multisort — 对多个数组或多维数组进行排序

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kevinfei 2019-08-01 10:33:10

循环4次数组的变化分别是: 1-> [1,2,3,1] 2-> [1,2,3,2] 3-> [1,2,3,3] 第三次value指向最后一个元素3 但是value是全局引用在上次循环指向了最后一个元素所以value=3的时候也会把最后一个元素的值改为3 4-> [1,2,3,3]

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