How to Build a PHP Function to Check Array Keys Without Using Built-In Functions

The array_key_exists function in PHP checks if a specific key exists in an array. Below is a custom implementation of this functionality without using PHP’s built-in array functions.

Code Example:

<?php
function custom_array_key_exists($key, $array) {
    // Loop through the array keys
    foreach ($array as $currentKey => $value) {
        // Check if the current key matches the specified key
        if ($currentKey === $key) {
            return true; // Key exists
        }
    }
    return false; // Key does not exist
}

// Example usage
$array = ['a' => 1, 'b' => 2, 'c' => 3];
$keyToCheck = 'b';

if (custom_array_key_exists($keyToCheck, $array)) {
    echo "The key '$keyToCheck' exists in the array.";
} else {
    echo "The key '$keyToCheck' does not exist in the array.";
}

Explanation:

1. Input Parameters:
   • $key: The key to check for in the array.
   • $array: The array to search in.
2. Loop Through the Array:
   • Use a foreach loop to iterate over the array.
   • Compare each key ($currentKey) with the specified key ($key) using a strict comparison (===).
3. Return Value:
   • If a match is found, return true.
   • If the loop completes without finding a match, return false.

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