PHP Data Types: int, float, string, bool, array, null

PHP has eight types you use every day: int, float, string, bool, array, object, null, plus callable for functions you pass around. A variable has no fixed type; its current value does. var_dump($x) shows both the type and the value, and gettype($x) returns the type as a string.

<?php
$values = [42, 3.14, "hello", true, [1, 2, 3], null, new stdClass()];

printf("%-8s %-10s %s\n", "gettype", "debug", "value");
foreach ($values as $value) {
    printf("%-8s %-10s %s\n", gettype($value), get_debug_type($value), json_encode($value));
}

The first column is gettype(), the second get_debug_type(). Replace a value with your own and run it again. They disagree on a few names: gettype says integer, double and boolean for historical reasons, while get_debug_type uses the names from type declarations (int, float, bool) and gives the class name for an object.

The PHP types at a glance

Inspect values with var_dump

var_dump is the tool for seeing what you really have. It prints the type, the value, and for strings the length in bytes:

<?php
var_dump(10);
var_dump(10.0);
var_dump("10");
var_dump(true);
var_dump(null);
var_dump(["id" => 7, "tags" => ["php", "web"]]);
var_dump("café");   // 5 bytes: é takes two bytes in UTF-8

echo would print 10 for the first three and hide the difference. The length in string(5) "café" counts bytes, which is why strlen and mb_strlen differ for non-ASCII text.

Integers and floats

An integer is a whole number. Literals can use underscores for readability, and hex, octal and binary notation. A float is any number with a decimal point or exponent, and like in every language it stores most decimals approximately:

<?php
$population = 8_100_000_000;   // underscores are ignored
var_dump($population);
var_dump(0xFF, 0b1010, 0o17);  // hex, binary, octal
var_dump(PHP_INT_MAX);
var_dump(PHP_INT_MAX + 1);     // too big: becomes a float

var_dump(7 / 2);               // / returns a float when needed
var_dump(8 / 2);               // and an int when the result is whole
var_dump(intdiv(7, 2));        // integer division

var_dump(0.1 + 0.2);
var_dump(0.1 + 0.2 == 0.3);
var_dump(abs((0.1 + 0.2) - 0.3) < PHP_FLOAT_EPSILON);

Never compare floats with ==; compare the difference against a small tolerance, or round both sides first. For money, store whole cents as integers.

Booleans and which values are false

A bool is true or false. Where PHP expects a condition (if, while, !), any value is converted to bool, and a short list of values counts as false: false, 0, 0.0, "", "0", [] and null. Everything else is true. The table shows each value with its type, its bool conversion and whether it is numeric:

The surprises are "0.0", " " and "null": all three are non-empty strings other than "0", so they are true, and if ($value) runs its body for them.

Arrays, objects and null

An array holds any mix of values under integer or string keys. An object is an instance of a class; stdClass is PHP's empty class for quick objects, and (object) turns an array into one. null means "no value":

<?php
$user = ["name" => "Ada", "roles" => ["admin", "editor"]];
echo gettype($user), ": ", $user["name"], "\n";

$point = new stdClass();
$point->x = 3;
$point->y = 4;
echo get_debug_type($point), ": ", $point->x, ",", $point->y, "\n";

$config = (object) ["debug" => true];
echo get_debug_type($config), ": debug is ", var_export($config->debug, true), "\n";

class Product
{
    public function __construct(public string $name, public float $price) {}
}
$p = new Product("Lamp", 25.0);
echo get_debug_type($p), ": {$p->name}\n";

$nothing = null;
var_dump($nothing, is_null($nothing));

Check a type with is_* functions

Each type has a test function that returns true or false. is_numeric is different from is_int: it accepts numeric strings too, which is what you want when checking form input.

<?php
$tests = [5, 5.0, "5", "5.5", " 5", "abc", true, null];

printf("%-7s %-6s %-8s %-9s %-10s\n", "value", "is_int", "is_float", "is_string", "is_numeric");
foreach ($tests as $t) {
    printf(
        "%-7s %-6s %-8s %-9s %-10s\n",
        var_export($t, true),
        is_int($t) ? "yes" : "",
        is_float($t) ? "yes" : "",
        is_string($t) ? "yes" : "",
        is_numeric($t) ? "yes" : ""
    );
}

Others: is_bool, is_array, is_object, is_null, is_callable, is_iterable, and $x instanceof ClassName for a specific class.

Type juggling and strict types

PHP converts types automatically when an operator needs a different one. A numeric string used in arithmetic becomes a number, and . turns numbers into strings. A string that is not numeric at all cannot be added, and PHP 8 throws a TypeError:

<?php
var_dump("10" + 5);        // int(15)
var_dump("1.5" * 2);       // float(3)
var_dump(10 . " items");   // string
var_dump("10" == "1e1");   // both numeric strings: compared as numbers
var_dump(100 == "1e2");

try {
    var_dump("abc" + 1);
} catch (TypeError $e) {
    echo "TypeError: ", $e->getMessage(), "\n";
}

Typed parameters convert too, unless the file starts with declare(strict_types=1);. Then a call with the wrong scalar type fails instead of being converted:

<?php
declare(strict_types=1);

function addVat(float $net): float
{
    return $net * 1.2;
}

echo addVat(100), "\n";          // int to float is still allowed

try {
    echo addVat("100"), "\n";    // a string is not converted in strict mode
} catch (TypeError $e) {
    echo "TypeError: ", $e->getMessage(), "\n";
}

To convert on purpose, cast: (int) "42", (float) "3.5", (string) 10, (bool) "0". The type casting page covers every cast and its edge cases.

Common mistake: comparing different types with ==

Because == converts before comparing, two values of different types can be "equal" in ways that cause bugs, such as "1e1" == "10" (both are the number 10) or null == false. Use ===, which also requires the same type, unless you want the conversion:

<?php
$pairs = [["1e1", "10"], [null, false], [0, ""], ["abc", 0], [1.0, 1]];

foreach ($pairs as [$a, $b]) {
    $show = var_export($a, true) . " vs " . var_export($b, true);
    printf("%-16s ==  %-6s ===  %s\n", $show, var_export($a == $b, true), var_export($a === $b, true));
}

PHP 8 fixed the worst case: "abc" == 0 used to be true and is now false, because a non-numeric string is compared as a string. The full tables are on the comparison operators page.