Analysis of usage of each and list in PHP_php skills

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.Usage of each

Look at the API first

array each ( array &$array )

This is described in the API: each — returns the current key/value pair in the array and moves 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
*/
&#63;>

2.list usage

Let’s see what the API says first

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

Let’s look at an example:

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

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
&#63;>

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

Why is this notice~40~20 returned?

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: start assigning values ​​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 gives a warning

3. Use each and list to implement array traversal

<&#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;>

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