isset() vs. array_key_exists(): When Should I Use Which in PHP?

Differences Between isset() and array_key_exists()

In programming, it's often essential to check if a specific key is present in an array. In PHP, this can be achieved using either the isset() or array_key_exists() functions. Let's explore the key differences between these two functions.

Key-Existence Verification

Both isset() and array_key_exists() verify if a key exists in an array. However, they differ in their criteria.

• array_key_exists(): Only checks for the presence of the key, regardless of its value or type.
• isset(): Checks not only for key presence but also ensures that the corresponding value is not null.

For example:

$a = ['key1' => 'foo', 'key2' => null];

array_key_exists('key1', $a); // true
array_key_exists('key2', $a); // true

isset($a['key1']); // true
isset($a['key2']); // false

Array Existence Verification

Another key distinction is that isset() does not generate an error if the array itself doesn't exist. In contrast, array_key_exists() does.

For instance:

isset($b); // No error
array_key_exists('key', $b); // Error: Undefined variable

Performance

isset() is generally faster than array_key_exists() because it doesn't perform any array-range checking.

Usage Scenarios

• Use array_key_exists() when you need to verify the existence of a key, regardless of its value.
• Use isset() when you want to check for the presence of a key and ensure that its value is not null.

Ultimately, choosing which function to use depends on the specific requirements of your application.

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