Syntax

Ints can be specified in decimal (base 10), hexadecimal (base 16), octal (base 8) or binary (base 2) notation. The negation operator can be used to denote a negative int.

To use octal notation, precede the number with a 0 (zero). As of PHP 8.1.0, octal notation can also be preceded with 0o or 0O. To use hexadecimal notation precede the number with 0x. To use binary notation precede the number with 0b.

As of PHP 7.4.0, integer literals may contain underscores (_) between digits, for better readability of literals. These underscores are removed by PHP's scanner.

Example #1 Integer literals

<?php
$a = 1234; // decimal number
$a = 0123; // octal number (equivalent to 83 decimal)
$a = 0o123; // octal number (as of PHP 8.1.0)
$a = 0x1A; // hexadecimal number (equivalent to 26 decimal)
$a = 0b11111111; // binary number (equivalent to 255 decimal)
$a = 1_234_567; // decimal number (as of PHP 7.4.0)
?>

Formally, the structure for int literals is as of PHP 8.1.0 (previously, the 0o or 0O octal prefixes were not allowed, and prior to PHP 7.4.0 the underscores were not allowed):

decimal     : [1-9][0-9]*(_[0-9]+)*
            | 0

hexadecimal : 0[xX][0-9a-fA-F]+(_[0-9a-fA-F]+)*

octal       : 0[oO]?[0-7]+(_[0-7]+)*

binary      : 0[bB][01]+(_[01]+)*

integer     : decimal
            | hexadecimal
            | octal
            | binary

The size of an int is platform-dependent, although a maximum value of about two billion is the usual value (that's 32 bits signed). 64-bit platforms usually have a maximum value of about 9E18. PHP does not support unsigned ints. int size can be determined using the constant PHP_INT_SIZE, maximum value using the constant PHP_INT_MAX, and minimum value using the constant PHP_INT_MIN.

Integer overflow

If PHP encounters a number beyond the bounds of the int type, it will be interpreted as a float instead. Also, an operation which results in a number beyond the bounds of the int type will return a float instead.

Example #2 Integer overflow

<?php
$large_number = 50000000000000000000;
var_dump($large_number);         // float(5.0E+19)

var_dump(PHP_INT_MAX + 1);       // 32-bit system: float(2147483648)
                                 // 64-bit system: float(9.2233720368548E+18)
?>

Integer division

There is no int division operator in PHP, to achieve this use the intdiv() function. 1/2 yields the float 0.5. The value can be cast to an int to round it towards zero, or the round() function provides finer control over rounding.

Example #3 Divisions

<?php
var_dump(25/7);         // float(3.5714285714286)
var_dump((int) (25/7)); // int(3)
var_dump(round(25/7));  // float(4)
?>

Converting to integer

To explicitly convert a value to int, use the (int) cast. However, in most cases the cast is not needed, since a value will be automatically converted if an operator, function or control structure requires an int argument. A value can also be converted to int with the intval() function.

If a resource is converted to an int, then the result will be the unique resource number assigned to the resource by PHP at runtime.

From booleans

false will yield 0 (zero), and true will yield 1 (one).

From floating point numbers

When converting from float to int, the number will be rounded towards zero. As of PHP 8.1.0, a deprecation notice is emitted when implicitly converting a non-integral float to int which loses precision.

Example #4 Casting from Float

<?php

function foo($value): int {
  return $value;
}

var_dump(foo(8.1)); // "Deprecated: Implicit conversion from float 8.1 to int loses precision" as of PHP 8.1.0
var_dump(foo(8.1)); // 8 prior to PHP 8.1.0
var_dump(foo(8.0)); // 8 in both cases

var_dump((int) 8.1); // 8 in both cases
var_dump(intval(8.1)); // 8 in both cases
?>

If the float is beyond the boundaries of int (usually +/- 2.15e+9 = 2^31 on 32-bit platforms and +/- 9.22e+18 = 2^63 on 64-bit platforms), the result is undefined, since the float doesn't have enough precision to give an exact int result. No warning, not even a notice will be issued when this happens!

Note:
NaN, Inf and -Inf will always be zero when cast to int.

Warning

Never cast an unknown fraction to int, as this can sometimes lead to unexpected results.

<?php
echo (int) ( (0.1+0.7) * 10 ); // echoes 7!
?>

See also the warning about float precision.

From strings

If the string is numeric or leading numeric then it will resolve to the corresponding integer value, otherwise it is converted to zero (0).

From NULL

null is always converted to zero (0).

From other types

Caution

The behaviour of converting to int is undefined for other types. Do not rely on any observed behaviour, as it can change without notice.

Integers

See Also