The PHP function isset() is often used to determine the presence of a variable. When the variable is not defined, false is returned. Using isset() is also an easy way to determine whether an array has a given key.
$assoc = array('key' => 'value'); echo isset($assoc['key']) ? 'true' : 'false'; // true echo isset($assoc['missing']) ? 'true' : 'false'; // false |
There is a catch: isset() called on a null variable will return false.
$var = null; echo isset($var) ? 'true' : 'false'; // false $array = array('key' => null); echo isset($array['key']) ? 'true' : 'false'; // false |
For checking the presence of a key in an array, use the PHP function array_key_exists() instead.
echo array_key_exists('key', $array) ? 'true' : 'false'; // true function has_empty($key, &$array) { return array_key_exists($key, $array) && !$array[$key]; } echo has_empty('key', $array) ? 'true' : 'false'; // true |
To determine the presence of a null variable, a custom function is required.
function isvar($var) { return isset($var) || @is_null($var); } $null = null; echo isvar($null) ? 'true' : 'false'; // true |
