PHP check if False or Null

Checking variable ( a few examples )

if(is_null($x) === true) // null
if($x === null) // null
if($x === false)
if(isset($x) === false) // variable undefined or null
if(empty($x) === true) // check if variable is empty (length of 0)

Isset() checks if a variable has a value including ( False , 0 , or Empty string) , But not NULL. Returns TRUE if var exists; FALSE otherwise.

On the other hand the empty() function checks if the variable has an empty value empty string , 0, NULL ,or False. Returns FALSE if var has a non-empty and non-zero value.

ISSET checks the variable to see if it has been set, in other words, it checks to see if the variable is any value except NULL or not assigned a value. ISSET returns TRUE if the variable exists and has a value other than NULL. That means variables assigned a " ", 0, "0", or FALSE are set, and therefore are TRUE for ISSET.

EMPTY checks to see if a variable is empty. Empty is interpreted as: " " (an empty string), 0 (0 as an integer), 0.0 (0 as a float), "0" (0 as a string), NULL, FALSE, array() (an empty array), and "$var;" (a variable declared, but without a value in a class.

isset — Determine if a variable is set and is not NULL

$a = "test";
$b = "anothertest";

var_dump(isset($a));      // TRUE
var_dump(isset($a, $b)); // TRUE

unset ($a);

var_dump(isset($a));     // FALSE

empty — Determine whether a variable is empty

<?php
$var = 0;

// Evaluates to true because $var is empty
if (empty($var)) {
  echo '$var is either 0, empty, or not set at all';
}

// Evaluates as true because $var is set
if (isset($var)) {
  echo '$var is set even though it is empty';
}
?>

It is important to use the correct function / notation, not just whatever appears to work correctly. There are a few things to consider that are not mentioned in the existing answers.

• Use isset to check if a variable has either not been set or has been set to null.
• Use empty to check if a variable == false. null is cast to false and as with isset, no notice is thrown if the variable has not been set.

if (!$variable) or if ($variable == false) is the same as empty, except that a notice will be thrown if the variable has not been set.

if ($variable !== null) is the same as isset, except that a notice will be thrown if the variable has not been set.

NB

if (!$variable) and if ($variable !== null) perform better than their respective functions but not when notices are being generated, therefore, $variable needs to have been set. Don't suppress notices as a micro-optimisation, as this will make your code harder to debug and even suppressed notices cause a performance penalty.

Coalescing operators

If you are checking a variable so that you can assign a value to it, then you should use ??, ?: instead of if statements.

??

?? assigns a value when not equal to null. $variable = $a ?? $b is the same as:

if (isset($a))
    $variable = $a;
else
    $variable = $b;

?:

?: assigns a value when not == to false. $variable = $a ?: $b is the same as:

if ($a)
    $variable = $a;
else
    $variable = $b;

but remember that a notice will be generated when $a has not been set. If $a might not have been set, you can use $variable = !empty($a) ? $a : $b; instead.

• check false: if ($v === false)
• check null: if (is_null($v))

empty() is an evil.It is slow,and when $v queals false,0,'0',array(),'',it will return true.if you need this kind of checking,you can use if ($v).