`isset()` vs. `array_key_exists()`: When Should I Use Each Function in PHP?

Difference Between isset() and array_key_exists()

In PHP, when working with arrays, you may encounter the need to check if a specific key exists within the array. Two common functions used for this purpose are isset() and array_key_exists().

isset()

isset() checks if a variable exists in the current scope and has a value other than NULL. When applied to an array, it determines if the specified key exists and its associated value is not NULL.

array_key_exists()

array_key_exists(), on the other hand, exclusively focuses on key existence within an array. It checks if the provided key is present in the array, regardless of its associated value.

Key Differences

The key differences between isset() and array_key_exists() are:

• Value Consideration: isset() considers the value associated with the key, while array_key_exists() only considers the key's presence.
• Existence vs. NULL: isset() returns true for existing keys with non-NULL values, while array_key_exists() returns true for existing keys regardless of their associated values.
• Non-Existing Arrays: isset() does not throw an error when the array does not exist, whereas array_key_exists() does.

Example Usage

Consider the following array:

$a = array('key1' => 'value1', 'key2' => null);

• isset($a['key1']): Returns true because the key exists and its value is not NULL.
• isset($a['key2']): Returns false because the key exists but its value is NULL.
• array_key_exists('key1', $a): Returns true because the key exists in the array.
• array_key_exists('key2', $a): Returns true because the key exists in the array, even though its value is NULL.

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