PHP empty(), isset() and "0": Handling Empty Form Values

“Empty” has several meanings in PHP. Choose the check that matches the question you are asking.

Question	Use
Was the key sent at all?	`isset($_POST["x"])` or `array_key_exists()`
Is the text blank?	`trim($value) === ""`
Is the value falsy (`0`, `""`, `"0"`, `null`, `[]`)?	`empty($value)`
Is the array empty?	`$array === []` or `count($array) === 0`

The “0” trap

index.php

PHP

<?php
$quantity = "0";

var_dump(empty($quantity));
var_dump(trim($quantity) === "");

Output

OUTPUT

1
2

bool(true)
bool(false)

A visitor who types 0 for a quantity or an age gave a valid answer. empty() says it is empty. The comparison with "" gets it right.

Optional fields

An optional field may be missing or blank. Turn blank into null, so the rest of your code has one rule.

index.php

PHP

<?php
$_POST = ["name" => "Isha", "phone" => "   "];

$phone = trim($_POST["phone"] ?? "");
$phone = $phone === "" ? null : $phone;

var_dump($phone);

Output

OUTPUT

NULL

A default for a missing value

index.php

PHP

<?php
$_POST = [];

$sort = $_POST["sort"] ?? "newest";

echo $sort;

Output

OUTPUT

newest

Blank vs missing vs zero

index.php

PHP

<?php
$tests = [
    "missing" => null,
    "blank" => "",
    "spaces" => "   ",
    "zero" => "0",
    "text" => "hello",
];

foreach ($tests as $label => $value) {
    $blank = $value === null || trim($value) === "";
    echo str_pad($label, 8) . ($blank ? "blank" : "has a value") . "\n";
}

Output

OUTPUT

missing blank
blank   blank
spaces  blank
zero    has a value
text    has a value

Checkboxes

An unchecked checkbox is missing from the request. Treat “missing” as false.

index.php

PHP

<?php
$_POST = [];

$agree = isset($_POST["agree"]);

var_dump($agree);

Output

OUTPUT

bool(false)

Numbers

For numeric input, validate with filter_var() and compare with === false, so that 0 stays valid.

index.php

PHP

<?php
$value = filter_var("0", FILTER_VALIDATE_INT);

var_dump($value !== false);

Output

OUTPUT

bool(true)

lightbulb

One helper

Put your “is this blank?” rule in one small function and reuse it. Then every field in the project treats "0", spaces and missing keys the same way.