How to Check if a Key Exists in an Associative Array in PHP?

Given an Associative array, the task is to check whether a key exists in the associative array or not. There are two methods to check if a key exists in an associative array, these are – using array_key_exists(), and isset() functions. Let’s explore each method with detailed explanations and code examples.

Approach 1: Using array_key_exists() Function

The array_key_exists() function checks if a specified key exists in an array. It returns true if the key exists and false otherwise.

PHP

<?php

$student_marks = array(
    "Maths" => 95, 
    "Physics" => 90,   
    "Chemistry" => 96, 
    "English" => 93,   
    "Computer" => 98
);

// Check if the key exists in the array
if (array_key_exists('Physics', $student_marks)) {
    echo "Key exists in the array";
} else {
    echo "Key does not exist in the array";
}

?>

Output

Key exists in the array

Approach 2: Using isset() Function

The isset() function checks if a variable is set and is not null. When used with an array, it checks if a specified key exists in the array and is not null.

PHP

<?php

$student_marks = array(
    "Maths" => 95, 
    "Physics" => 90,   
    "Chemistry" => 96, 
    "English" => 93,   
    "Computer" => 98
);

// Check if the key exists in the array
if (isset($student_marks['Physics'])) {
    echo "Key exists in the array";
} else {
    echo "Key does not exist in the array";
}

?>

Output

Key exists in the array