PHP--Usage of each and list list for each safe each list as value i js traverse list collection eac-PHP Tutorial-php.cn

PHP--Usage of each and list list for each safe each list as value i js traverse list collection eac

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Release： 2016-07-29 08:53:18

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1.Usage of each
Let’s 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?

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

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2.list usage
Let’s first see what the API says
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:

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

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Yes, you can assign values to a set of variables
Let’s look at another example:

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

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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 ] ranafter: from right to LeftOpenStart EndowmentValue ,Endowed worth ShunPreface is c=arr[3] b= arr[1 ]a=arr[0]
So c=20b = 40 Because there is no arr[0], $a gave a warning
3. Use each and list to implement array traversal

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

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The above introduces the usage of PHP--each and list, including the content of each and list. I hope it will be helpful to friends who are interested in PHP tutorials.