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PHP : Language Reference : Types : Integers

Integers

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

See also: Arbitrary length integer / GMP, Floating point numbers, and Arbitrary precision / BCMath

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 2.1. Integer literals

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<?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:

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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 2.2. Octal weirdness

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<?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.

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<?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.

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<?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().

See also type-juggling.

From booleans

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

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.

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<?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.

Code Examples / Notes » language.types.integer

rickard_cedergren
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('');
     }
  }

jmw254
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";
}

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'

me
This note applies to machines that are using a 32 bit integer size.  I imagine the same results occur in 64 bit machines as well (with the number 2^63-1).
-2147483648 falls into the range of 32 bit signed integers (0b10000000000000000000000000000000), yet php treats it as a float.  However, -2147483647-1 is treated as an integer.
The following code demonstrates:
<?php
var_dump(-2147483648); //float(-2147483648)
var_dump(-2147483647 - 1); //int(-2147483648)
?>
Regards

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;
   }

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

d_n
Here are some tricks to convert from a "dotted" IP address to a LONG int, and backwards. This is very useful because accessing an IP addy in a database table is very much faster if it's stored as a BIGINT rather than in characters.
IP to BIGINT:
<?php
 $ipArr    = explode('.',$_SERVER['REMOTE_ADDR']);
 $ip       = $ipArr[0] * 0x1000000
           + $ipArr[1] * 0x10000
           + $ipArr[2] * 0x100
           + $ipArr[3]
           ;
?>
IP as BIGINT read from db back to dotted form:
Keep in mind, PHP integer operators are INTEGER -- not long. Also, since there is no integer divide in PHP, we save a couple of S-L-O-W floor (<division>)'s by doing bitshifts. We must use floor(/) for $ipArr[0] because though $ipVal is stored as a long value, $ipVal >> 24 will operate on a truncated, integer value of $ipVal! $ipVint is, however, a nice integer, so
we can enjoy the bitshifts.
<?php
       $ipVal = $row['client_IP'];
       $ipArr = array(0 =>
                   floor(  $ipVal               / 0x1000000) );
       $ipVint   = $ipVal-($ipArr[0]*0x1000000); // for clarity
       $ipArr[1] = ($ipVint & 0xFF0000)  >> 16;
       $ipArr[2] = ($ipVint & 0xFF00  )  >> 8;
       $ipArr[3] =  $ipVint & 0xFF;
       $ipDotted = implode('.', $ipArr);
?>

rustamabd@gmail-you-know-what
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

popefelix
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.

paul
"always round it downwards"
It seems to truncate, or round toward zero, rather than downward. If the float is negative, it is rounded up.

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