How to check if a variable is NULL in PHP?
NULL stands for a variable without value. To check if a variable is NULL you can either use is_null($var) or the comparison (===) with NULL. Both ways, however, generate a warning if the variable is not defined. Similar to isset($var) and empty($var), which can be used as functions. isset($var) returns true(boolean) if the passed variable is defined and contains a value unequal to NULL. empty($var) returns true(boolean), if the passed variable is not defined or contains an empty value. Here “empty” is defined in a very general way and also includes 0(integer), false(boolean), or the empty string.
Example : is_null($var), isset($var) and ($var === null)
<?php
$var = null;
echo('$var with the value NULL:' . "\n\n");
var_dump(is_null($var)); // true
var_dump($var === null); // true
var_dump(!isset($var)); // true
var_dump(empty($var)); // true
echo("\n\n");
echo('undefined variable $var2:' . "\n\n");
var_dump(is_null($var2)); // true
var_dump($var2 === null); // true
var_dump(!isset($var2)); // true
var_dump(empty($var2)); // true
?>
Output:
$var with the value NULL: bool(true) bool(true) bool(true) bool(true) undefined variable $var2: Notice: Undefined variable: var2 in [...][...] on line 15 bool(true) Notice: Undefined variable: var2 in [...][...] on line 16 bool(true) bool(true) bool(true)
Comparison of the results: is_null(), ===, isset() and empty()
The following table shows the differences between is_null(), ===, isset() and empty():
"" (String) |
"0" (String) |
|||||
|---|---|---|---|---|---|---|
| is_null($var) | true | false | false | false | false | false |
| ($var === null) | true | false | false | false | false | false |
| isset($var) | false | true | true | true | true | true |
| empty($var) | true | true | true | true | true | true |
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