PHP check if False or Null

Question

I also get confused how to check if a variable is false/null when returned from a function.

When to use empty() and when to use isset() to check the condition ?

Answer 1

For returns from functions, you use neither isset nor empty, since those only work on variables and are simply there to test for possibly non-existing variables without triggering errors.

For function returns checking for the existence of variables is pointless, so just do:

if (!my_function()) {
    // function returned a falsey value
}

To read about this in more detail, see The Definitive Guide To PHP's isset And empty.

Answer 2

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)

Answer 3

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.

Answer 4

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.

Answer 5

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';
}
?>

Answer 6

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.

Answer 7

• 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).