isset

(PHP 4, PHP 5, PHP 7)

issetDetermine if a variable is declared and is different than NULL


Description

isset ( mixed $var , mixed ...$vars ) : bool

Determine if a variable is considered set, this means if a variable is declared and is different than NULL.

If a variable has been unset with the unset() function, it is no longer considered to be set.

isset() will return FALSE when checking a variable that has been assigned to NULL. Also note that a null character ("\0") is not equivalent to the PHP NULL constant.

If multiple parameters are supplied then isset() will return TRUE only if all of the parameters are considered set. Evaluation goes from left to right and stops as soon as an unset variable is encountered.


Parameters

var
The variable to be checked.
vars
Further variables.


Return Values

Returns TRUE if var exists and has any value other than NULL. FALSE otherwise.


Examples

Example #1 isset() Examples

<?php$var = ;// This will evaluate to TRUE so the text will be printed.if (isset($var)) {    echo "This var is set so I will print.";}// In the next examples we'll use var_dump to output// the return value of isset().$a = "test";$b = "anothertest";var_dump(isset($a));      // TRUEvar_dump(isset($a, $b)); // TRUEunset ($a);var_dump(isset($a));     // FALSEvar_dump(isset($a, $b)); // FALSE$foo = NULL;var_dump(isset($foo));   // FALSE?>

This also work for elements in arrays:

<?php$a = array ('test' => 1, 'hello' => NULL, 'pie' => array('a' => 'apple'));var_dump(isset($a['test']));            // TRUEvar_dump(isset($a['foo']));             // FALSEvar_dump(isset($a['hello']));           // FALSE// The key 'hello' equals NULL so is considered unset// If you want to check for NULL key values then try: var_dump(array_key_exists('hello', $a)); // TRUE// Checking deeper array valuesvar_dump(isset($a['pie']['a']));        // TRUEvar_dump(isset($a['pie']['b']));        // FALSEvar_dump(isset($a['cake']['a']['b']));  // FALSE?>

Example #2 isset() on String Offsets

PHP 5.4 changes how isset() behaves when passed string offsets.


<?php$expected_array_got_string = 'somestring';var_dump(isset($expected_array_got_string['some_key']));var_dump(isset($expected_array_got_string[0]));var_dump(isset($expected_array_got_string['0']));var_dump(isset($expected_array_got_string[0.5]));var_dump(isset($expected_array_got_string['0.5']));var_dump(isset($expected_array_got_string['0 Mostel']));?>

Output of the above example in PHP 5.3:


bool(true)
bool(true)
bool(true)
bool(true)
bool(true)
bool(true)

Output of the above example in PHP 5.4:


bool(false)
bool(true)
bool(true)
bool(true)
bool(false)
bool(false)

Notes

Warning isset() only works with variables as passing anything else will result in a parse error. For checking if constants are set use the defined() function.


Note:

Because this is a

language construct and not a function, it cannot be called using variable functions.

Note:

When using isset() on inaccessible object properties, the __isset() overloading method will be called, if declared.

See Also