PHP Type Casting: String to Int, intval() and (int)

To convert a value to another type, put the type in parentheses before it: (int) "42" gives the integer 42. The function form intval("42") does the same. Casting never fails: text that is not a number becomes 0, and a string that starts with digits keeps only those digits.

<?php
$input = "42";

var_dump((int) $input);
var_dump(intval($input));
var_dump((int) "12abc");   // leading digits only
var_dump((int) "abc");     // not a number at all
var_dump((float) "3.14");
var_dump((string) 99);
var_dump((bool) "0");

The casts PHP has are (int), (float), (string), (bool), (array) and (object). Each also has a function: intval(), floatval(), strval(), boolval().

String to int: what (int) and intval() return

PHP reads digits from the start of the string, after skipping leading whitespace, and stops at the first character that does not fit a number. Exponent notation counts as a number, a 0x prefix does not.

<?php
$samples = ["42", "  42", "-17", "12.7", "1e3", "12abc", "abc", "", "0x1A", "012"];

foreach ($samples as $s) {
    printf("%-8s => %d\n", var_export($s, true), (int) $s);
}

Note "12.7" becomes 12: casting to int cuts off the fraction, it does not round. Neither (int) nor intval() prints a warning here, whatever the input.

intval() with a base

intval($value, $base) reads the string in another number system. With base 0, PHP looks at the prefix: 0x for hex, 0b for binary, a leading 0 for octal.

<?php
var_dump(intval("ff", 16));
var_dump(intval("101", 2));
var_dump(intval("777", 8));
var_dump(intval("0x1A", 0));
var_dump(intval("0b101", 0));
var_dump(intval("012", 0));    // octal because of the leading 0
var_dump(intval("012"));       // base 10 by default

// Converting the other way
echo dechex(255), " ", decbin(5), " ", base_convert("ff", 16, 2), "\n";

Float to int: truncation, not rounding

(int) drops everything after the decimal point, toward zero. Round first if you want the nearest whole number, and watch the parentheses:

<?php
var_dump((int) 12.99);
var_dump((int) -12.99);
var_dump((int) round(12.5));

// Precedence: the cast applies to (0.1 + 0.7) before * 10
var_dump((int) (0.1 + 0.7) * 10);
var_dump((int) ((0.1 + 0.7) * 10));
var_dump((int) round((0.1 + 0.7) * 10));

The last pair is the classic float trap: (0.1 + 0.7) * 10 is stored as 7.999999..., so truncating gives 7. Rounding first gives 8. The [math page](/docs/php/math) covers round, floor and ceil.

Casting to bool, string and array

To bool, only a handful of values become false: 0, 0.0, "", "0", null and []. Everything else is true, including "0.0", " " and "false".

To string, true becomes "1", while false and null both become "". Floats drop a trailing .0, and very large or small floats use exponent notation.

<?php
foreach (["0", "0.0", " ", "false", [], [0], 0.0, -1, null] as $v) {
    printf("%-10s => %s\n", json_encode($v), var_export((bool) $v, true));
}

echo "---\n";
var_dump((string) true, (string) false, (string) null);
var_dump((string) 3.0, (string) 0.1, (string) 1e25);

echo "---\n";
var_dump((array) "a");     // a scalar becomes a one-element array
var_dump((array) null);    // null becomes an empty array

Casting an array to a string does not join it. This prints Tags: Array:

<?php
$tags = ["php", "web"];
echo "Tags: " . $tags;

and PHP adds a warning:

Warning: Array to string conversion in /home/index.php on line 3

Use implode(", ", $array) or json_encode($array) to turn an array into text.

Every cast at a glance

Pick a value to see what intval, (bool), strval, is_numeric and gettype return for it. Every cell was computed by PHP 8.3.

Point at or tap a cell to read it as PHP.

$x	intval	bool	strval	is_numeric	gettype
"10"	10	true	'10'	true	'string'
"1abc"	1	true	'1abc'	false	'string'
"abc"	0	true	'abc'	false	'string'
""	0	false	''	false	'string'
" "	0	true	' '	false	'string'
"0"	0	false	'0'	true	'string'
"0.0"	0	true	'0.0'	true	'string'
"1e1"	10	true	'1e1'	true	'string'
"010"	10	true	'010'	true	'string'
1.5	1	true	'1.5'	true	'double'
true	1	true	'1'	false	'boolean'
false	0	false	''	false	'boolean'
null	0	false	''	false	'NULL'
[]	0	false	"Array" + warning	false	'array'
[1, 2]	1	true	"Array" + warning	false	'array'

Every cell computed by PHP 8.3.19.

Numeric strings and automatic conversion

A numeric string is a string that looks like a number: "12", "-3.5", "1e3", with optional whitespace around it. PHP converts these automatically in arithmetic, and is_numeric() tells you whether a string qualifies.

<?php
foreach (["12", "12.5", "1e3", " 12", "12 ", "12abc", "0x1A", ""] as $s) {
    printf("%-8s is_numeric: %s\n", var_export($s, true), var_export(is_numeric($s), true));
}

echo "---\n";
var_dump("5" * "4");     // both numeric: int
var_dump("5" + 1.5);     // float
var_dump(10 . "");       // int to string with concatenation

"12abc" + 1 still gives 13, but PHP 8 prints Warning: A non-numeric value encountered, and "abc" + 1 throws a TypeError. Cast or validate before doing arithmetic on user input.

settype() and gettype()

settype() changes the type of a variable in place and gettype() reports it. get_debug_type() returns the shorter names you see in error messages (int, float, string).

<?php
$value = "42";
echo gettype($value), "\n";

settype($value, "integer");
var_dump($value);
echo gettype($value), " / ", get_debug_type($value), "\n";

$price = "19.90";
settype($price, "float");
var_dump($price);

Most code uses a cast ($value = (int) $value;) instead, because it is shorter and reads the same.

Validate input instead of casting it

(int) never says no, so (int) "abc" silently becomes 0 and (int) "5 apples" becomes 5. For form input, use filter_var with FILTER_VALIDATE_INT: it returns the integer or false.

<?php
foreach (["42", " 42 ", "42abc", "4.2", "042", "-7", "abc"] as $input) {
    $n = filter_var($input, FILTER_VALIDATE_INT);
    printf("%-8s => %s\n", var_export($input, true), $n === false ? "rejected" : $n);
}

Compare the result with === false, because 0 is a valid integer and == false would reject it. The filter_var page shows ranges and other validators.