Last updated: Fri, 01 Jun 2007

Integers

An integer is a number of the set Z = {..., -2, -1, 0, 1, 2, ...}.

Syntax

Integers can be specified in decimal (10-based), hexadecimal (16-based) or octal (8-based) notation, optionally preceded by a sign (- or +).

If you use the octal notation, you must precede the number with a 0 (zero), to use hexadecimal notation precede the number with 0x.

Example 11.1. Integer literals


<?php

$a = 1234; // decimal number

$a = -123; // a negative number

$a = 0123; // octal number (equivalent to 83 decimal)

$a = 0x1A; // hexadecimal number (equivalent to 26 decimal)

?>

Formally the possible structure for integer literals is:


decimal     : [1-9][0-9]*
            | 0

hexadecimal : 0[xX][0-9a-fA-F]+

octal       : 0[0-7]+

integer     : [+-]?decimal
            | [+-]?hexadecimal
            | [+-]?octal

The size of an integer is platform-dependent, although a maximum value of about two billion is the usual value (that's 32 bits signed). PHP does not support unsigned integers. Integer size can be determined from PHP_INT_SIZE, maximum value from PHP_INT_MAX since PHP 4.4.0 and PHP 5.0.5.

Warning

If an invalid digit is passed to octal integer (i.e. 8 or 9), the rest of the number is ignored.

Example 11.2. Octal weirdness


<?php

var_dump(01090); // 010 octal = 8 decimal

?>

Integer overflow

If you specify a number beyond the bounds of the integer type, it will be interpreted as a float instead. Also, if you perform an operation that results in a number beyond the bounds of the integer type, a float will be returned instead.


<?php

$large_number =  2147483647;

var_dump($large_number);

// output: int(2147483647)



$large_number =  2147483648;

var_dump($large_number);

// output: float(2147483648)



// it's true also for hexadecimal specified integers between 2^31 and 2^32-1:

var_dump( 0xffffffff );

// output: float(4294967295)



// this doesn't go for hexadecimal specified integers above 2^32-1:

var_dump( 0x100000000 );

// output: int(2147483647)



$million = 1000000;

$large_number =  50000 * $million;

var_dump($large_number);

// output: float(50000000000)

?>

Warning

Unfortunately, there was a bug in PHP so that this does not always work correctly when there are negative numbers involved. For example: when you do -50000 * $million, the result will be -429496728. However, when both operands are positive there is no problem.

This is solved in PHP 4.1.0.

There is no integer division operator in PHP. 1/2 yields the float 0.5. You can cast the value to an integer to always round it downwards, or you can use the round() function.


<?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 integer, use either the (int) or the (integer) cast. However, in most cases you do not need to use the cast, since a value will be automatically converted if an operator, function or control structure requires an integer argument. You can also convert a value to integer with the function intval().

From booleans

FALSE will yield 0 (zero), and TRUE will yield 1 (one).

From floating point numbers

When converting from float to integer, the number will be rounded towards zero.

If the float is beyond the boundaries of integer (usually +/- 2.15e+9 = 2^31), the result is undefined, since the float hasn't got enough precision to give an exact integer result. No warning, not even a notice will be issued in this case!

Warning

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


<?php

echo (int) ( (0.1+0.7) * 10 ); // echoes 7!

?>

See for more information the warning about float-precision.

From strings

See String conversion to numbers

From other types

Caution

Behaviour of converting to integer is undefined for other types. Currently, the behaviour is the same as if the value was first converted to boolean. However, do not rely on this behaviour, as it can change without notice.

add a note User Contributed Notes
Integers

Jacek
10-Mar-2007 12:51


On 64 bits machines max integer value is 0x7fffffffffffffff (9 223 372 036 854 775 807).

09-Mar-2007 03:26


To force the correct usage of 32-bit unsigned integer in some functions, just add '+0'  just before processing them.



for example 

echo(dechex("2724838310"));

will print '7FFFFFFF'

but it should print 'A269BBA6'



When adding '+0' php will handle the 32bit unsigned integer

correctly

echo(dechex("2724838310"+0));

will print 'A269BBA6'

popefelix at gmail dot com
21-Dec-2006 02:50


Be careful when using integer conversion to test something to see if it evaluates to a positive integer or not.  You might get unexpected behaviour.



To wit:

<?php

error_reporting(E_ALL);

require_once 'Date.php';



$date = new Date();

print "\$date is an instance of " . get_class($date) . "\n";

$date += 0;

print "\$date is now $date\n";

var_dump($date);



$foo = new foo();

print "\$foo is an instance of " . get_class($foo) . "\n";

$foo += 0;

print "\$foo is now $foo\n";

var_dump($foo);



class foo {

    var $bar = 0;

    var $baz = "la lal la";

    var $bak;



    function foo() {

        $bak = 3.14159;

    }

}

?>



After the integer conversion, you might expect both $foo and $date to evaluate to 0.  However, this is not the case:



$date is an instance of Date



Notice: Object of class Date could not be converted to int in /home/kpeters/work/sketches/ObjectSketch.php on line 7

$date is now 1

int(1)

$foo is an instance of foo



Notice: Object of class foo could not be converted to int in /home/kpeters/work/sketches/ObjectSketch.php on line 13

$foo is now 1

int(1)



This is because the objects are first converted to boolean before being converted to int.

rustamabd@gmail-you-know-what
12-Dec-2006 09:42


Be careful with using the modulo operation on big numbers, it will cast a float argument to an int and may return wrong results. For example:

<?php

    $i = 6887129852;

    echo "i=$i\n";

    echo "i%36=".($i%36)."\n";

    echo "alternative i%36=".($i-floor($i/36)*36)."\n";

?>

Will output:

i=6.88713E+009

i%36=-24

alternative i%36=20

jmw254 at cornell dot edu
25-Aug-2006 05:14


Try this one instead: 



function iplongtostring($ip)

{

    $ip=floatval($ip); // otherwise it is capped at 127.255.255.255



    $a=($ip>>24)&255;

    $b=($ip>>16)&255;

    $c=($ip>>8)&255;

    $d=$ip&255;



    return "$a.$b.$c.$d";

}

rickard_cedergren at yahoo dot com
27-Jan-2005 09:15


When doing large subtractions on 32 bit unsigned integers the result sometimes end up negative. My example script converts a IPv4 address represented as a 32 bit unsigned integer to a dotted quad (similar to ip2long()), and adds a "fix" to the operation. 



   /**************************

    * int_oct($ip) 

    * Convert INTeger rep of IP to octal (dotted quad)

    */

   function int_oct($ip) {



      /* Set variable to float */

      settype($ip, float);



      /* FIX for silly PHP integer syndrome */

      $fix = 0;

      if($ip > 2147483647) $fix = 16777216;



      if(is_numeric($ip)) {

         return(sprintf("%u.%u.%u.%u",

                $ip / 16777216,

                (($ip % 16777216) + $fix) / 65536,

                (($ip % 65536) + $fix / 256) / 256,

                ($ip % 256) + $fix / 256 / 256

                )

     );

      }

      else {

         return('');

      }

   }

23-Dec-2003 06:18


Sometimes you need to parse an unsigned

32 bit integer. Here's a function I 've used:

                                                                                

    function parse_unsigned_int($string) {

        $x = (float)$string;

        if ($x > (float)2147483647)

            $x -= (float)"4294967296";

        return (int)$x;

    }

add a note

Floating point numbers

Booleans

Last updated: Fri, 01 Jun 2007