What is subscript in php array

In PHP arrays, the subscript is the identifier of the array element. Each element in the array is distinguished by a special identifier called a key (also called a subscript); the subscript defaults to an integer type and starts from 0. In PHP, if you do not manually set the string key name (subscript) when creating an array, an index array will be created by default. Its subscript (key name) consists of an integer value, and the default index value increases sequentially starting from 0. ;Each number corresponds to the position of an array element in the array and does not need to be specified.

The operating environment of this tutorial: windows7 system, PHP8.1 version, DELL G3 computer

Under the php array Label (key name)

Array array is an ordered set of variables, where each value is called an element. Each element is distinguished by a special identifier called a key (also called a subscript).

The subscript can be a number (integer) or a string, but the default is an integer type and starts from 0.

You can use the following two methods to declare an array in PHP:

• You can declare an array by directly assigning values ​​to the array elements;

• Use the array() function to declare an array.

But no matter which method, if you do not manually set the string key name (subscript) when creating the array, the index array will be created by default

<?php
header(&#39;content-type:text/html;charset=utf-8&#39;);   
$array[] = &#39;苹果&#39;;
$array[] = &#39;香蕉&#39;;
$array[] = &#39;梨&#39;;
$array[] = &#39;桃子&#39;;
var_dump($array);
?>

<?php
header(&#39;content-type:text/html;charset=utf-8&#39;);   
$array = array(&#39;红色&#39;,&#39;黄色&#39;,&#39;蓝色&#39;,&#39;白色&#39;);

var_dump($array);
?>

The subscript (key name) of the index array consists of integer values ​​and starts from 0 by default. Each number corresponds to the position of an array element in the array. It is not required Specifically, PHP will automatically assign an integer value to the key name of the index array, and then automatically increment from this value.

Only when the string key name is manually specified, the associative array will be set:

<?php
header(&#39;content-type:text/html;charset=utf-8&#39;);   
$array = array("id"=>25,"name"=>"李华","age"=>18);

var_dump($array);
?>

How to get the array subscript in PHP

array_key() function can obtain some or all key names (subscripts) in the array. The syntax format of this function is as follows:

array_keys($array,$search_value,$strict)

The parameter description is as follows:

• $array: required parameter, which is the array to be operated;
• $search_value: Optional parameter. If the parameter is empty, the function will return all the key names in the array. If this parameter is specified, the function will only return the key name with the value $search_value;
• $strict: Optional parameter to determine whether to use strict mode when searching. $strict defaults to false, which is non-strict mode. Only types are compared during search, not types. If $strict is set to true, that is Strict mode, compares both value and type when searching, equivalent to ===.

array_key() function will return the obtained array key name in the form of an array.

Example 1: All key names

<?php
$arr=array("Peter"=>65,"Harry"=>80,"John"=>78,"Clark"=>90);
var_dump($arr);
var_dump(array_keys($arr));
?>

Example 2: Key names of specified values

<?php
$arr=array("Peter"=>65,"Harry"=>80,"John"=>78,"Clark"=>90);
var_dump($arr);
var_dump(array_keys($arr,80));
var_dump(array_keys($arr,"80"));
var_dump(array_keys($arr,"80",true));
?>

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