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 ?

Solution 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.

Solution 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)

Solution 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.

Solution 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.

Solution 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';
}
?>

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Comments

[Gromski]

empty is not evil, you simply do not understand its use case. May I direct you to The Definitive Guide To PHP's isset And empty?

[Gromski]

A variable cannot not have an assigned value. The value is at least null.

[Harsha M V]

i am actually trying to catch a return array or false and trying to determine further what to do

[Gromski]

OK? So $return = myfunction(); if (!$return) { // 't was false! }

[Gromski]

@tkoom Would you be happier if the syntax was more operator-like?

[ducin]

@deceze, if empty is not a function, it'd be nice if it didn't pretend one. And it does and it confuses programmers, just as a lot of things does (see me.veekun.com/blog/2012/04/09/php-a-fractal-of-bad-design)

[grasevski]

Note that this also catches empty strings and empty arrays and 0 and '0', which might not be what you want

[ToolmakerSteve]

Your comment on empty not quite correct: empty also returns true for values that are equivalent to 0.

[mickmackusa]

ToolmakerSteve is correct, the explanation of what empty() does is misleading for researchers.