How does PHP determine whether a certain key or index exists in an array?

In PHP, you can use the built-in function array_key_exists() to determine whether a key or index exists in the array. The following article will introduce you to the PHP array_key_exists() function. I hope it will be helpful to you.

array_key_exists()

array_key_exists() function checks whether a specified key exists in an array name, returns true if the key name exists, false if the key name does not exist.

Tip: Please remember that if you omit the key name when specifying the array, integer key names will be generated starting from 0 and increasing by 1.

Syntax:

array_key_exists(key,array)

Parameters:

• key: required, given key name or index, which can be any value that can be used as an array index.

• array: required, specifies the array.

Example 1: Check whether the key name "Toyota" exists in the array:

<?php
header("content-type:text/html;charset=utf-8");
$a = array("Volvo" => "XC90", "BMW" => "X5");
if (key_exists("Toyota", $a)) {
	echo "Key存在！";
} else {
	echo "Key不存在！";
}
?>

Output:

Key不存在！

Example 2: Check whether the integer key name "0" exists in the array:

<?php
header("content-type:text/html;charset=utf-8");
$a = array("Volvo", "BMW");
if (array_key_exists(0, $a)) {
	echo "Key存在！";
} else {
	echo "Key不存在！";
}
?>

Output:

Key存在！

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