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本文实例分析了PHP中each与list用法。分享给大家供大家参考,具体如下:

1.each的用法

先看API

array each ( array &$array )

api里是这么描述的:each — 返回数组中当前的键/值对并将数组指针向前移动一步

我们先来看看返回的数组是怎么样的?

<&#63;php 
$arr = array('你','若','安','好','便','是','晴','天');
print_r(each($arr));
print_r(each($arr));
echo '<hr />';
/*
返回
Array
(
  [1] => 你
  [value] => 你
  [0] => 0
  [key] => 0
)
Array
(
  [1] => 若
  [value] => 若
  [0] => 1
  [key] => 1
)
*/
//执行相同的一段代码,从‘你'到‘若',说明each是会每执行一次,游标向数组尾部移动一步
//0和Key存放的是键
//1和value存放的是值
//因此each满足遍历数组的,得到当前的键和值,以及每执行一次,向尾部移动一步游标
//因此循环数组也可以用each这么写
reset($arr);
for(;$tmp=each($arr);){
  echo $tmp[0],'~',$tmp[1],'<br />';
}
/*
返回
0~你
1~若
2~安
3~好
4~便
5~是
6~晴
7~天
*/
&#63;>

2.list的用法

先看api是怎么说的

像 array() 一样,这不是真正的函数,而是语言结构。list()用一步操作给一组变量进行赋值。  

来看一个例子:

<&#63;php 
list($a,$b)=array(10,20);
echo $a,'~',$b,'<br />';
//返回10~20
&#63;>

没错可以给一组变量赋值

再来看另外一个例子:

<&#63;php 
list($a,$b,,$c)=array(2=>10,3=>20,4=>30,1=>40);
echo $a,'~',$b,'~',$c,'<br />';
//返回notice~40~20
//执行到$a的时候返回给我一个notice:说数组没有0键
&#63;>

按照一般的想法应该会返回:10~20~40

为什么会返回这个notice~40~20呢?

答:这涉及到list的运行机制,list是这么赋值的

首先:不要管右边的数组,看List里面的变量,从左到右应该是  $a = arr[0]   $b=arr[1]  $c=arr[3]

然后:从右到左开始赋值,赋值的顺序是 $c=arr[3]  $b=arr[1]  $a=arr[0]

所以$c=20  $b = 40  因为没有arr[0],所以$a给了一个警告

3.用each和list实现数组的遍历

<&#63;php 
$arr = array('你','若','安','好','便','是','晴','天');
for(;list($k,$v)=each($arr);){
  echo $k,'~',$v,'<br />';
}
/*
return:
0~你
1~若
2~安
3~好
4~便
5~是
6~晴
7~天
*/
&#63;>

希望本文所述对大家PHP程序设计有所帮助。

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