isset() vs. array_key_exists(): What's the Difference in PHP Array Handling?

The Differences between isset() and array_key_exists()

When dealing with arrays in PHP, it's important to know the difference between two key functions: isset() and array_key_exists().

isset() vs. array_key_exists()

isset() checks if a key or variable exists in an array or variable scope.

array_key_exists() specifically checks if a key exists within an array.

Key Comparisons

Existing Key/Variable

For keys that exist and have a non-null value, both functions will return true:

$a = ['key' => 'value'];

isset($a['key']); // true
array_key_exists('key', $a); // true

Non-Existing Key/Variable

For keys that do not exist, only array_key_exists() will return false:

$a = [];

isset($a['key']); // false
array_key_exists('key', $a); // false

Null Value Key

Here's the crucial difference: isset() returns false for keys with null values, while array_key_exists() returns true:

$a = ['key' => null];

isset($a['key']); // false
array_key_exists('key', $a); // true

Non-Array Variables

Unlike array_key_exists(), isset() can check if a variable exists, regardless of its type:

$name = 'John Doe';

isset($name); // true
array_key_exists($name, []); // Fatal error

Conclusion

Both isset() and array_key_exists() have their uses, but it's important to understand their differences. isset() checks for the existence of a key or variable, including null values. array_key_exists() strictly checks for the existence of a key within an array and ignores null values.

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