PHP isset() Function
Quick summary: The PHP isset() construct checks whether a variable is set and not null.
PHP isset() Syntax
isset(mixed ...$values): boolPHP
PHP isset() Basic examples
$a = null;
var_dump(isset($a));PHP
Output:
bool(false)Returns false when the value is null.
$b = 0;
var_dump(isset($b));PHP
Output:
bool(true)Zero values are considered set.
PHP isset() Real-world usage
if (isset($_GET['page'])) {
echo 'Page set';
}PHP
Output:
Page setChecks if request parameters exist.
PHP isset() Edge cases
var_dump(isset(['a'=>null]['a']));PHP
Output:
bool(false)Returns false for null array values.
PHP isset() Common mistakes
Using isset to detect null keys
isset cannot detect null values.
Incorrect
isset(['a'=>null]['a']);Correct
array_key_exists('a', ['a'=>null]);Use array_key_exists for null values.
PHP isset() Frequently Asked Questions
What does isset() do?
Checks if a variable is set and not null.
Use case?
Avoid undefined variable errors.
Return type?
bool.
Common mistake?
Confusing with empty().
Handles null?
Returns false.
Supports multiple variables?
Yes.
Performance?
Very fast.
Safe?
Yes.
Works with arrays?
Yes.
Alternative?
array_key_exists().
Used in forms?
Yes.
Best practice?
Use for existence checks.