A brief analysis of how the keys in the php array are arranged

PHP is a widely used open source server-side scripting language that is widely used in the field of web development. Among them, array is one of the most basic data types in PHP and is widely used to store, operate and process a set of related data. In PHP, arrays can use different types of keys to access their elements, including integers, strings, Boolean values, etc. So, in PHP, how are the keys in the array arranged? This article will introduce it to you in detail.

1. The key in the PHP array can be any legal PHP data type

In PHP, the key of the array can be an integer, a string, a floating point number, or a Boolean value etc. for any legal PHP data type. This means that elements in an array can be identified by any data type. For example:

//以字符串作为key的数组
$fruits = array("apple" => "苹果", "banana" => "香蕉", "cherry" => "樱桃");

//以整数作为key的数组
$numbers = array(1 => "one", 2 => "two", 3 => "three");

//以布尔值作为key的数组
$values = array(true => "真", false => "假");

2. Array keys in PHP are arranged according to the order of addition

When creating a PHP array, the order in which elements are added determines their position in the array . In other words, array keys in PHP are actually arranged according to the order of addition. For example:

//以整数作为key的数组
$numbers = array();
$numbers[1] = "one";
$numbers[3] = "three";
$numbers[2] = "two";
print_r($numbers); //输出：Array ( [1] => one [3] => three [2] => two )

You can see that in the above code, the order of adding elements is 1, 3, 2, but the order in the output array is 1, 3, 2. This is because array keys in PHP are actually sorted according to the order of addition, not according to the element value size or the data type of the key.

3. When using a non-numeric key, PHP will automatically convert the key's data type

In PHP, when using a non-numeric key, PHP will automatically convert the key's data type Convert to string. This means that if you use an integer as a key, the integer will be converted to the corresponding string. For example:

//以整数作为key的数组
$numbers = array();
$numbers[1] = "one";
$numbers[3] = "three";
$numbers["2"] = "two";
print_r($numbers); //输出：Array ( [1] => one [3] => three [2] => two )

You can see that in the above code, although key "2" is actually a string, it is treated as an integer 2 and added to the array. At this point, since the integer 2 has already appeared in the array, it is overwritten. Therefore, the final output array only contains elements 1, 3, and 2, but not "2".

4. In PHP7, array keys can maintain the insertion order

In PHP7 and above, the new array syntax can use the [] operator to declare an array. Unlike the old syntax, the new syntax maintains insertion order when declaring an array. For example:

//使用 [] 操作符保持插入顺序的数组
$numbers = [1 => "one", 3 => "three", 2 => "two"];
print_r($numbers); //输出：Array ( [1] => one [3] => three [2] => two )

You can see that in PHP7 and above, arrays declared using the new [] operator can also maintain the insertion order without using additional functions to sort them.

Summary

In PHP, the keys in the array are actually arranged according to the order of addition. Any legal PHP data type can be used as an array key, and non-numeric keys will be converted to strings. In PHP7 and above, you can use the new [] operator to declare an array, which maintains the order of insertion. Therefore, when using PHP arrays, developers need to pay attention to using appropriate key types and ensure that the order of keys is explicitly specified or use a new declaration method to avoid potential errors.

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