Analysis of usage of each and list in PHP

This article analyzes the usage of each and list in PHP with examples. Share it with everyone for your reference, the details are as follows:

1. How to use each

First look at the API

array each (array &$array)

The API describes it like this: each — returns the current item in the array Key/value pairs and move the array pointer forward one step

Let's first take a look at what the returned array looks like?

<&#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
*/
?>

2. How to use list

Let’s first look at what the API says

Like array(), this is not a real function, but a language structure. list() assigns values ​​to a set of variables in one step.

Let’s look at an example:

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

Yes, you can assign values ​​to a set of variables

Let’s look at another example:

<&#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
?>

According to the general idea, it should return: 10~20~40

Why? What about returning this notice~40~20?

Answer: This involves the operating mechanism of the list. This is how the list is assigned

First of all: ignore the array on the right and look at the variables in the List. From left to right it should be $a = arr[0] $b=arr [1] $c=arr[3]

Then: assignment starts from right to left, the order of assignment is $c=arr[3] $b=arr[1] $a=arr[0]

So$ c=20 $b = 40 Because there is no arr[0], $a gave a warning

3. Use each and list to implement array traversal

<?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
*/
?>

I hope this article will be helpful to everyone in PHP programming. .

The above has introduced the analysis of the usage of each and list in PHP, including relevant aspects. I hope it will be helpful to friends who are interested in PHP tutorials.