Three small functions help you check what a variable holds and remove it. You will use them constantly, especially with form data.
isset(): does it exist and is it not null?
index.php
PHP
<?php
$name = "Rhea";
$nothing = null;
var_dump(isset($name));
var_dump(isset($nothing));
var_dump(isset($missing));
Output
OUTPUT
bool(true)
bool(false)
bool(false)isset() is true only when the variable exists and is not null. It never gives a warning, even for a variable that does not exist, so it is the safe way to test.
You can pass several variables. The answer is true only if all of them are set.
index.php
PHP
<?php
$a = 1;
$b = 2;
var_dump(isset($a, $b));
var_dump(isset($a, $c));
Output
OUTPUT
bool(true)
bool(false)empty(): is it “empty”?
empty() is true for a variable that is missing or holds a value that PHP treats as empty:
""(an empty string)0and0.0"0"(the string zero)nullandfalse[](an empty array)
index.php
PHP
<?php
var_dump(empty(""));
var_dump(empty("0"));
var_dump(empty(0));
var_dump(empty("hello"));
var_dump(empty([]));
Output
OUTPUT
bool(true)
bool(true)
bool(true)
bool(false)
bool(true)
dangerous
The "0" trap
A person might legitimately type
0 in a form (a quantity or an age). empty("0") is true, so you would reject a valid value. For form fields, compare with "" instead. Handling Empty Values goes deeper.unset(): remove a variable
index.php
PHP
<?php
$token = "abc123";
unset($token);
var_dump(isset($token));
Output
OUTPUT
bool(false)unset() also removes an item from an array.
index.php
PHP
<?php
$user = ["name" => "Rhea", "password" => "secret"];
unset($user["password"]);
print_r($user);
Output
OUTPUT
Array
(
[name] => Rhea
)
lightbulb
Quick rule
Use
isset() to ask “is there a value?” and empty() to ask “is there a useful value?”. When 0 or “0” is a valid input, use isset() and a strict comparison instead of empty().