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.

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)



// this doesn't go for hexadecimal specified integers:

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.

User Contributed Notes
Integers

rickard_cedergren at yahoo dot com
27-Jan-2005 04:15


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('');

      }

   }

dave at burtonsys dot com
04-Jun-2004 09:42


Matt, you need to also preserve the minus sign.

Negative integers are integers, too.

-Dave

23-Dec-2003 01:18


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;

    }

Matt AKA junkie
29-Jul-2003 06:46


Let's say we're in the situation, let's say a from a form, and the what you want from them is an integer. To be nice though, we're going to fix their error of adding anything other than an integer instead of telling them to do it.



function make_int($str) {

# Let's make sure this isn't being done for no reason

if (gettype($str)!="integer") {

# First we'll make it into a "float" (physically speaking) if not already one

$i = preg_replace("/[^0-9.]/", "", $str);

# Then we make it an integer physically

$i = preg_replace("/\.[0-9]*$/", "", $i);

# Finally, we define the integer as an integer

$i = (int) $i;

return $i;

} else {

return $str;

}}



Just to reiterate, this will take the "string" (not the type) inputted, and make it an integer.

swiftouch at yahoo dot com
27-Jun-2003 08:08


If you were to accidentally  precede a number with: +- or -+ ...as in:



$yada = +-1234;



will default to a negative number

or:



$yada = -+1234;



The (-) negative will always take precedence.



This is, of course, if you precede a number with -+ or +- by accident.

adam at forsalebyowner dot com
12-Feb-2003 06:19


Whoah.  The lack of support for > 32 bit integers is really a pain for some things.  Anyway, for bitwise operations requiring a > 32 bit number:



($big42bitInteger & $someSmallInteger)



You can move to mysql or some other db if you're using one anyway:



select id,($big42bitInteger & $someSmallInteger) as isBitwiseAND FROM someTable;



if ($row->isBitwiseAND > 0) {



do stuff;

}

laercio at gcsnet dot com dot br
02-Nov-2002 08:02


Hi,



To easily solve this problem of math operations compile your PHP with --enable-bcmath and use its set of intruction:

 bcadd, bccomp, bcdiv, bcmod, bcmul, bcpow, bcscale, bcsqrt, bcsub. 

No more flotpoint problems. 

The intruction can be found on this manual.



Laercio Fortes

kennyc at horizondigital dot com
14-Jun-2002 09:57


ONELINE LEADING ZERO ADDER: I kept getting frustrated by php's weak number formatting functions and using the recursive leading zero adders that I've seen in other people code, so here's my quick and easy oneliner for adding leading zero's to any number:



Two digit space:

substr($num+100,1);

0=00

5=05

23=23

3.14=03.14



Four digit space:

substr($num+10000,1);

0=0000

5=0005

23=0023

256=0256

4096=4096

98.6=0098.6



You may want to check first to be sure that your number dosen't already exceed it's character size!

tim at freeman dot little-possums dot net dot invalid
15-Jan-2002 03:20


> there is no risk of rounding errors when doing (int)(n1/n2).



This is not quite true.  Although both n1 and n2 can be represented exactly in a float, their quotient often cannot be.  It is not even guaranteed that for floating-point arithmetic, 6.0/3.0==2.0 exactly.  The floating-point answer may be 1.999...etc, which would round down to 1.

carl at NOSPAM dot thep dot lu dot se
22-Aug-2001 08:51


One note about integer division:


PHP of course has the << and >> operators, so as long as you need to do integer division by a power of 2 you can just shift to the right.


However, as the floating point numbers are 64-bit rather than 32-bit all possible values for a 32-bit int can be represented exactly by a float, so there is no risk of rounding errors when doing (int)(n1/n2).


The overhead of converting to float and back can probably be ignored for an interpreted language like PHP, unless the engine is insanely optimized. (Testing confirms that $a/$b takes only marginally longer than $a>>$b and $a*$b for integers $a and $b.)