PHP empty(): Check for Empty Strings, Arrays and 0

empty($var) returns true if the variable does not exist or its value is falsy: null, false, 0, 0.0, "", "0" or an empty array []. For any other value it returns false. Like isset(), it never warns about undefined variables or array keys.

<?php
$name = "";
$items = [];
$count = 0;
$city = "Paris";

var_dump(empty($name));
var_dump(empty($items));
var_dump(empty($count));
var_dump(empty($city));
var_dump(empty($notDefined));

if (empty($items)) {
    echo "Your cart is empty\n";
}

empty($x) is the same as !isset($x) || !$x. In other words: missing, or converts to false.

Which values are empty

Pick a value in the table to see empty() next to isset() and the (bool) cast. Every cell was computed by PHP 8.3.

The surprises are at both ends: "0" is empty, while " " (a space), "0.0", "null" and [0] are not.

"0" is empty: the classic bug

Because "0" is falsy, empty() treats a quantity of 0, a score of 0 or a PIN of "0" as "nothing entered". This bites in forms, where every value arrives as a string.

<?php
$submitted = ["quantity" => "0", "comment" => "", "pin" => "0"];

foreach ($submitted as $field => $value) {
    $byEmpty = empty($value) ? "missing" : "ok";
    $byString = trim($value) === "" ? "missing" : "ok";
    printf("%-9s %-4s empty(): %-8s trim() === '': %s\n",
        $field, var_export($value, true), $byEmpty, $byString);
}

For text input, the reliable check for "nothing entered" is trim($value) === "". Keep empty() for values where 0 really means nothing.

Check if a string is empty

To test for an empty string exactly, compare with "". To also treat whitespace as empty, trim first. Since PHP 5.5 empty() accepts expressions, so empty(trim($s)) works too (but has the same "0" problem).

<?php
$tests = ["", "   ", "0", "hello", null];

foreach ($tests as $s) {
    printf("%-8s === '': %-5s  trim === '': %-5s  empty(): %s\n",
        var_export($s, true),
        var_export($s === "", true),
        var_export(trim($s ?? "") === "", true),
        var_export(empty($s), true));
}

trim() does not accept null without a deprecation notice in PHP 8.1 and later, which is why the block writes trim($s ?? "").

Check if an array is empty

For arrays, empty($arr), $arr === [] and count($arr) === 0 all give the same answer. empty() has the advantage of working on a variable or key that may not exist.

<?php
$cart = [];
$tags = ["php"];
$order = ["lines" => []];

var_dump(empty($cart), $cart === [], count($cart) === 0);
var_dump(empty($tags));
var_dump(empty($order["lines"]));
var_dump(empty($order["discounts"]));   // key not there at all

// An array of empty values is not empty
var_dump(empty(["", null, 0]));

// To ignore blank entries, filter first
var_dump(empty(array_filter(["", null, 0])));

array_filter() without a callback removes every falsy value, so it is a quick way to ask "does this array hold anything real".

Validate a required form field

!empty() is a common way to require a field, as long as 0 is not a valid answer. Run this block, leave the fields blank and press Send, then fill them in and send again: the script runs once more with $_POST filled in.

<?php
$errors = [];
$sent = ($_SERVER["REQUEST_METHOD"] ?? "GET") === "POST";

if ($sent) {
    if (empty($_POST["email"])) {
        $errors[] = "Email is required.";
    }
    if (empty($_POST["terms"])) {
        $errors[] = "Please accept the terms.";
    }
    // Age 0 is invalid anyway, but "" must be caught: here empty() fits
    if (empty($_POST["age"]) || !ctype_digit($_POST["age"])) {
        $errors[] = "Age must be a whole number.";
    }
}
?>
<form method="post">
  <p><label>Email <input name="email" value="<?= htmlspecialchars($_POST["email"] ?? "") ?>"></label></p>
  <p><label>Age <input name="age" value="<?= htmlspecialchars($_POST["age"] ?? "") ?>"></label></p>
  <p><label><input type="checkbox" name="terms" value="1" <?= empty($_POST["terms"]) ? "" : "checked" ?>> I accept the terms</label></p>
  <button>Send</button>
</form>
<?php if ($sent && !$errors): ?>
  <p style="color:#0a7">Thanks, all fields are valid.</p>
<?php endif; ?>
<?php foreach ($errors as $e): ?>
  <p style="color:#c33"><?= $e ?></p>
<?php endforeach; ?>

empty($_POST["terms"]) covers both cases for the checkbox: not sent at all, or sent with an empty value. The forms page goes further with per-field error messages.

empty vs isset

Both are safe on undefined variables and keys. They answer different questions:

<?php
$values = ["null" => null, "zero" => 0, "zero string" => "0", "empty string" => "", "space" => " ", "text" => "php"];

printf("%-13s %-7s %-7s %s\n", "", "isset", "empty", "!empty");
foreach ($values as $label => $v) {
    printf("%-13s %-7s %-7s %s\n", $label,
        var_export(isset($v), true),
        var_export(empty($v), true),
        var_export(!empty($v), true));
}

• isset($x): does it exist and is it not null? Use it for optional keys, checkboxes and "was this sent at all".
• !empty($x): does it exist and is it truthy? Use it for "has something real", when 0 and "0" do not count.
• $x === "" or $x === []: is it exactly empty? Use it when 0 is a valid value.

The isset page covers the other half, including isset() with several variables at once and the difference from array_key_exists().