CODEWITHSUNDEEP
phpscriptingvariables
Robin Rodricks
Robin Rodricks

Reputation: 113956

How to reset a variable to NULL in PHP?

I can use isset($var) to check if the variable is not defined or null. (eg. checking if a session variable has been set before)

But after setting a variable, how do I reset it to the default such that isset($var) returns false?

Upvotes: 29

Views: 68434

Answers (5)

Gregory Neely
Gregory Neely

Reputation: 111

As of php 7.2 directly setting a variable is depreciated. You should not use it in this fashion you should look into using unset instead. https://www.php.net/manual/en/language.types.null.php

unset($v); will result in the same false when checking to see if the variable is null or unset. 

isset($v) === false 
is_null($v) === false

Upvotes: 0

mauris
mauris

Reputation: 43619

Further explanation:

While a variable can be null or not null, a variable can also be said to be set or not set.

to set a variable to null, you simply

$var = null;

This will make $var null, equivalent to false, 0 and so on. You will still be able to get the variable from $GLOBALS['var'] since it is still defined / set. However, to remove a variable from the global and/or local namespace, you use the

unset($var);

This will make $var not set at all. You won't be able to find in $GLOBALS.

Upvotes: 23

nickf
nickf

Reputation: 546035

As nacmartin said, unset will "undefine" a variable. You could also set the variable to null, however this is how the two approaches differ:

$x = 3; $y = 4;
isset($x);  // true;
isset($y);  // true;

$x = null;
unset($y);
isset($x);  // false
isset($y);  // false

echo $x;  // null
echo $y;  // PHP Notice (y not defined)

Upvotes: 26

leepowers
leepowers

Reputation: 38308

Also, you can set the variable to null:

<?php

$v= 'string';
var_dump(isset($v));
$v= null;
var_dump(isset($v));

?>

Upvotes: 2

nacmartin
nacmartin

Reputation: 2182

Use unset($var);

Upvotes: 49

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