Detailed explanation of php array function

This article mainly shares with you the detailed explanation of PHP array functions, mainly in the form of code and text. I hope it can help you.

Array

• The array belongs to composite type data

• The array is actually a Ordered mapping

Classification

索引数组     数组的下标（key）是数字

关联数组     数组的下标（key）是字符串

Whether it is an index array or an associative array, the value is found through the key.

Create

array() form

Create index array

array(value1,value2,value3...)

Example 1

// 通过array()创建下标连续的索引数组
$arr1 = array('A',2,false); 

输出结果：
    Array ( [0] => A [1] => 2 [2] => )
    false转换成空字符串

Example 2

//创建手动指定下标的数组
$arr2 = array(2=>'a',3=>true);

输出结果：
    Array ( [2] => a [3] => 1 )

Create associative array

array(key1=>value1, key2=>value2, key3=>value3...)

Example

// 定义关联数组
$userInfo = array(
    'username'=>'Tim',
    'age'=>23,
    'email'=>'404491216@qq.com'
);

print_r($userInfo);

输出结果：
    Array ( [username] => Tim 
            [age] => 23 
            [email] => 404491216@qq.com 
          )

[ ] form ( New in 5.4)

$arr = [value1,value2,value3...]

Example

// []创建数组
$arr = ['A','B',true,2];
print_r($arr);

输出结果：
    Array ( [0] => A [1] => B [2] => 1 [3] => 2 )

rang()

is used to create an index array with consecutive subscripts.

range(min, max(, 步进制))

Step system: how much each value differs from, the default is 1.

Example

// range()例子  值为1-10
$arr = range(1,10,2);
print_r($arr);

输出结果：
    Array
        (
            [0] => 1
            [1] => 3
            [2] => 5
            [3] => 7
            [4] => 9
        )

compact()

compact('变量名')

is used to create an associative array.

First define it in an external variable, and then pass in the variable to generate an array.

Note that variable names need to be enclosed in quotes.

Example

// compact()例子
$username = 'Tim';
$age = 23;
$email = 'xxx@xx.com';

// 注意，这里变量名需要用引号
$userInfo = compact('username','age','email');

输出结果：
    Array ( [username] => Tim [age] => 23 [email] => xxx@xx.com )

define()

define(key,value)

Example

define('TEST1',array('a','b','c'));
print_r(TEST1);

输出结果：
    Array ( [0] => a [1] => b [2] => c )

Loop

for loop

The for loop can only traverse index arrays with consecutive subscripts

Supplement:

count() gets the number of parameters in the array

If it is null, count() will return 0.

Example

// 使用rang()快速创建数组
$arr = range('a','d');

for($i=0; $i<$len; $i++){
    echo $arr[$i],&#39;<br/>&#39;;
}

输出结果：
    a,b,c,d

for each loop

只要value
foreach (数组名称 as $value)    

key和value 都要
foreach (数组名称 as $key => $value)

Note:

• Traverses the empty array, the loop body will not be executed;

• When traversing for each, a copy of the array is operated (php7 new feature)

• Traversing by reference has better iteration characteristics. Modification of the array will affect the loop (php7)

Example

// php7新特性——foreach操作的是数组的副本
$arr = [0,1,2];
$ref =&$arr;

foreach($arr as $v){
    echo $v,&#39;<br/>&#39;;

    // 老版本会删除1，但php7操作的是副本，所以没影响
    unset($arr[1]);
}

foreach输出结果：
    0 1 2

// 都是0、2   因为1被删除了
var_dump($arr,$ref);  

var_dump输出结果：
array (size=2)
  0 => int 0
  2 => int 2
)

Related recommendations:

Summary of common array functions in php

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