Can php array be empty?

In PHP programming, array is a very commonly used data type. It can store multiple values ​​and access them as key-value pairs. I believe that many PHP developers are familiar with arrays, but in practice, many developers will encounter a problem, that is: can PHP arrays be empty?

First, let us take a look at how PHP arrays are defined:

$array = array(); //空数组
$array = array(1, 2, 3); //带有三个元素的数组
$array = []; //PHP7.4和更高版本支持的空数组

In the above code, we can see that defining an empty array is very simple, just use array() or [] That’s it. However, for a novice, it is easy to fall into the misunderstanding that an array must have at least one element.

In fact, PHP arrays can be very flexible, and their elements can be of any type, including null values. Therefore, PHP arrays can be empty or have empty elements.

Let’s look at an example:

$array1 = array(); //空数组
$array2 = array(null); //只有一个元素，值为null
$array3 = array("", null, 0); //三个元素中有两个值为空

The above code demonstrates three different situations, in which $array1 is a completely empty array, $array2 is an array with only one element, and the The value is null, and $array3 is an array of three elements, two of which have empty values.

So, why can PHP arrays be empty? We can understand this problem from the internal implementation of the array itself.

In PHP, an array is actually a special variable type. An array variable can contain multiple values, and each value can be accessed with a key. However, a PHP array is not a true array, it is actually an associative array (a map) where the keys can be integers or strings and the values ​​can be of any type. This means that the PHP array implementation allows any combination of keys/values, including empty elements and empty arrays.

In addition, PHP's parser also treats null as a valid value. Therefore, $array = array(null) is a complete array containing only one element, and the value of this element is null. Similarly, $array = array("", null, 0) is a complete three-element array, two of which have null values.

To summarize, PHP arrays can be empty or have empty elements, and this is allowed by PHP's internal implementation. Therefore, in development, we should correctly understand the characteristics of PHP arrays and follow best practices to use them.

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