Note: isset() is a language construct.
Returns TRUE if var exists; FALSE otherwise.
If a variable has been unset with unset(), it will no longer be isset(). isset() will return FALSE if testing a variable that has been set to NULL. Also note that a NULL byte ("\0") is not equivalent to the PHP NULL constant.
<?php
$a = "test";
$b = "anothertest";
echo isset ($a); // TRUE
echo isset ($a, $b); //TRUE
unset ($a);
echo isset ($a); // FALSE
echo isset ($a, $b); //FALSE
$foo = NULL;
print isset ($foo); // FALSE
?> |
This also work for elements in arrays:
<?php
$a = array ('test' => 1, 'hello' => null);
echo isset ($a['test']); // TRUE
echo isset ($a['foo']); // FALSE
echo isset ($a['hello']); // FALSE
echo array_key_exists('hello', $a); // TRUE
?> |
See also empty(), unset(), and array_key_exists().