PHP empty() Function

PHP empty() checks whether a variable is empty. It returns true when the variable does not exist, or when it has a “false-like” value such as 0, empty string or NULL.

It is mostly used in form validation, for example to find out if the user left a field blank.

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Syntax

empty(mixed $var): bool

Parameters

Parameter	Description
var	Required. The variable or expression you want to check

Return value: true if the value is empty, otherwise false. empty() does not give any warning when the variable does not exist.

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Which values are empty?

All the values in this table are considered empty by PHP.

Value	empty() result
“” (empty string)	true
0 (integer)	true
0.0 (float)	true
“0” (string with zero)	true
NULL	true
false	true
[] (empty array)	true
Undefined variable	true
“0.0” (string)	false
” ” (a single space)	false
“Hello”	false
[0] (array with one item)	false

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Examples

Example #1: Check simple values

<?php
$a = "";
$b = 0;
$c = "Hello";

var_dump(empty($a));
var_dump(empty($b));
var_dump(empty($c));
?>

Output:

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Example #2: Undefined variable

The variable below is never created. empty() still works and gives true without any warning.

<?php
var_dump(empty($notDefined));
?>

Output:

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Example #3: String “0” and arrays

<?php
var_dump(empty("0"));
var_dump(empty([]));
var_dump(empty([0]));
?>

Output:

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Example #4: Form validation

A common use of empty() is to check if a required field is blank.

<?php
$username = "";

if (empty($username)) {
    echo "Please enter your username.";
} else {
    echo "Welcome, " . $username;
}
?>

Output:

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isset() vs empty()

Value	isset()	empty()
Undefined variable	false	true
NULL	false	true
“” (empty string)	true	true
0	true	true
“Hello”	true	false

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Common mistake: 0 is a valid value

Suppose a shop allows quantity 0. If you check it with empty(), PHP says it is empty and you show a wrong error message.

<?php
$quantity = 0;

// Wrong: 0 is a valid quantity but empty() returns true
if (empty($quantity)) {
    echo "Please enter quantity.";
}
?>

Output:

A better way is to check with isset() and compare with an empty string.

<?php
$quantity = 0;

if (!isset($quantity) || $quantity === "") {
    echo "Please enter quantity.";
} else {
    echo "Quantity is " . $quantity;
}
?>

Output:

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Summary

• empty() returns true for “”, 0, “0”, NULL, false, [] and undefined variables.
• It never gives a warning for undefined variable.
• empty($x) is same as !isset($x) || $x == false.
• Do not use empty() when 0 or “0” is a valid value.

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