PHP 5.4.31 Released

整数

integer は、ℤ = {..., -2, -1, 0, 1, 2, ...} という集合です。

以下も参照ください。

構文

整数 (integer) は、10 進数(基数 10)、16 進数 (基数 16)、8 進数 (基数 8) あるいは 2 進数 (基数 2) 表記で指定可能です。オプションで、符号(-または+)を前に付けることが可能です。

2 進数の整数リテラルは、PHP 5.4.0 から利用可能となりました。

8 進数表記を使用する場合、数の前に 0 (ゼロ) を付ける必要があります。また、16 進数表記を使用するには、数の前に 0x を付ける必要があります。 2 進数表記を使用する場合、数の前に 0b を付ける必要があります。

例1 整数リテラル

<?php
$a 
1234// 10進整数
$a = -123// 負の数
$a 0123// 8進数 (10進数の83と等価)
$a 0x1A// 16進数 (10進数の26と等価)
$a 0b11111111// 2進数 (10進数の255と等価)
?>

使用可能な整数リテラルの形式は以下のように定義されています。

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

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

octal       : 0[0-7]+

binary      : 0b[01]+

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

整数のサイズはプラットフォームに依存しますが、 約 20 億 (32 ビット符号付) が一般的な値です。 64 ビットプラットフォームでの通常の最大値は、およそ 9*10^18 (900京) になります。 しかし Windows は例外で、Windows は常に 32 ビットとなります。 PHP は符号無し整数をサポートしていません。 整数のサイズは定数 PHP_INT_SIZE で、 そして整数の最大値は定数 PHP_INT_MAX でそれぞれ決まります。 これらの定数は、PHP 4.4.0 以降および PHP 5.0.5 以降で使えます。

警告

8 進数の整数値として不正な数字(例: 8 または 9)が渡された場合、 数値の残りの部分は無視されます。

例2 おかしな 8 進数

<?php
var_dump
(01090); // 010(8 進数)= 8(10 進数)
?>

整数のオーバーフロー

integer型の範囲外の数を指定した場合、かわりに floatとして解釈されます。また、結果が integer型の範囲外の数となるような計算を行うと floatが代わりに返されます。

例3 32 ビットシステムにおける整数のオーバーフロー

<?php
$large_number 
2147483647;
var_dump($large_number);                     // int(2147483647)

$large_number 2147483648;
var_dump($large_number);                     // float(2147483648)

$million 1000000;
$large_number =  50000 $million;
var_dump($large_number);                     // float(50000000000)
?>

例4 64 ビットシステムにおける整数のオーバーフロー

<?php
$large_number 
9223372036854775807;
var_dump($large_number);                     // int(9223372036854775807)

$large_number 9223372036854775808;
var_dump($large_number);                     // float(9.2233720368548E+18)

$million 1000000;
$large_number =  50000000000000 $million;
var_dump($large_number);                     // float(5.0E+19)
?>

PHP には整数の割り算はありません。1/2 float 型の 0.5 になります。 下方向の整数値に値を丸めるためにキャストを使用することができ、 また、round() 関数を使用することもできます。

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

整数への変換

integer に値を明示的に変換するには、キャスト (int) または (integer) のどちらかを使用してください。しかし、多くの場合、演算子、関数、制御構造が integer 引数を必要とする場合、値は自動的に変換されるため、 キャストを使用する必要はありません。 関数 intval() を用いて値を整数に変換することも可能です。

resourceinteger に変換すると、その結果は一意なリソース番号となります。 これは、その resource に対して PHP が実行時に割り当てた番号です。

型の相互変換 を参照ください。

booleans から

FALSE は、0 (ゼロ) となり、 TRUE は、1 となります。

浮動小数点数から

float から整数に変換する場合、その数はゼロのほうに丸められます。

float が整数の範囲 (通常は、32 ビットプラットフォームでは +/- 2.15e+9 = 2^31、Windows 以外の 64 ビットプラットフォームでは +/- 9.22e+18 = 2^63 ) を越える場合、結果は undefined となります。これは、 その float が正しい整数の結果を得るために十分な精度を得られなかったからです。 この場合、警告も通知も発生しません!

警告

未知の端数を integer にキャストしないでください。 この場合、予期しない結果となることがあります。

<?php
echo (int) ( (0.1+0.7) * 10 ); // 7が出力されます!
?>

より詳細な情報については、 float の精度に関する注意を参照ください。

文字列から

文字列変換 を参照ください。

他の型から

警告

整数への変換の動作は、他の型については定義されません。 現在の動作は、その値がまず 論理値に変換された 場合と同じです。しかし、この動作は予告なく変更されることがありえるので、 これを前提にしてはいけません。

add a note add a note

User Contributed Notes 22 notes

up
23
Paul
6 years ago
"always round it downwards"

It seems to truncate, or round toward zero, rather than downward. If the float is negative, it is rounded up.
up
11
rustamabd@gmail-you-know-what
7 years ago
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
up
1
Alex
5 months ago
"The behaviour of converting to integer is undefined for other types. Do not rely on any observed behaviour, as it can change without notice."

actually i use type casting to output Boolean like this:

<?php
echo (int)(function_exists('imagecreatetruecolor'));
?>

so i see 0 or 1 in output
up
6
d_n at NOSPAM dot Loryx dot com
6 years ago
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);
?>
up
6
Anonymous
10 years ago
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;
    }
up
4
Anonymous
7 years ago
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'
up
3
Hamza Burak Ylmaz
5 years ago
<?php
//This is a simple function to return number of digits of an integer.

//function declaration
function count_digit($number)
{
   
$digit = 0;
    do
    {
       
$number /= 10;      //$number = $number / 10;
       
$number = intval($number);
       
$digit++;   
    }while(
$number!=0);
    return
$digit;
}

//function call
$num = 12312;
$number_of_digits = count_digit($num); //this is call :)
echo $number_of_digits;
//prints 5
?>
up
1
darkshire
6 years ago
d_n at NOSPAM dot Loryx dot com
13-Aug-2007 05:33
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]
            ;
?>

This can be written in a bit more efficient way:
<?php
  $ipArr   
= explode('.',$_SERVER['REMOTE_ADDR']);
 
$ip       = $ipArr[0]<<24
           
+ $ipArr[1]<<16
           
+ $ipArr[2] <<8
           
+ $ipArr[3]
            ;
?>

shift is more cheaper.
up
1
popefelix at gmail dot com
7 years ago
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.
up
0
pere dot cil at wanadoo dot fr
3 years ago
Please also note that the maximum stored in the integer depends on the platform / compilation; on windows xp 32 bits, the following value:

0x5468792130ABCDEF

echoes to:

6.0822444802213E+18 (cast to float)

On a fully 64 bits system, it echoes to:

6082244480221302255
up
-2
php at richardneill dot org
1 year ago
A leading zero in a numeric literal means "this is octal". But don't be confused: a leading zero in a string does not. Thus:
$x = 0123;          // 83
$y = "0123" + 0     // 123
up
-2
wbcarts at juno dot com
5 years ago
PHP offers a slew of built-in functions and automatic type-casting routines which can get pretty complicated. But most of the time, you still have to take matters into your own hands and allow PHP to do its thing. In that case, and something that has NOT been mentioned, is how to construct your code. To keep things simple, I divide all my scripts in half. The top half gives my scripts the "capability" they need, and the lower half is the actual code to be "run" or "executed".

<?php
/*
* build the program's capability - define variables and functions...
*/
$item_label = '';        // type string
$item_price = 0.0;       // type float
$item_qty = 1;           // type integer
$item_total = 0.0;       // type float - to set use calculate()

function calculate(){
  global
$item_price, $item_qty, $item_total;
 
$item_price = number_format($item_price, 2);
 
$item_total = number_format(($item_price * $item_qty), 2);
}

function
itemToString() {
  global
$item_label, $item_price, $item_qty, $item_total;
  return
"$item_label [price=\$$item_price, qty=$item_qty, total=\$$item_total]";
}

/*
* run the program - set data, call methods...
*/
$item_label = "Coffee";
$item_price = 3.89;
$item_qty = 2;
calculate();           // set $item_total
echo itemToString();   // -> Coffee [price=$3.89, qty=2, total=$7.78]

$item_label = "Chicken";
$item_price = .80;     // per lb.
$item_qty = 3.5;       // lbs.
calculate();           // set $item_total
echo itemToString();   // -> Chicken [price=$0.80, qty=3.5, total=$2.80]
?>
Note: All type-casting is done by PHP's built-in number_format() method. This allows our program to enter any number (float or int) on item price or quantity in the runtime part of our script. Also, if we explicitly cast values to integer in the capability part of our script, then we start getting results that may not be desirable for this program. For example, if in the calculate method we cast item_qty to integer, then we can no longer sell chicken by the pound!
up
-2
Jacek
7 years ago
On 64 bits machines max integer value is 0x7fffffffffffffff (9 223 372 036 854 775 807).
up
-3
rickard_cedergren at yahoo dot com
9 years ago
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('');
      }
   }
up
-4
iletras at yahoo dot com
3 years ago
//This is a (simpler ?) function to return number of digits of an integer.

//function declaration
function count_digit($number) {
  return  strlen((string) $number);
}

//function call
$num = 12312;
$number_of_digits = count_digit($num); //this is call :)
echo $number_of_digits;
//prints 5
up
-4
jmw254 at cornell dot edu
7 years ago
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";
}
up
-5
eric
6 years ago
In response to the comment by me at troyswanson dot net:

-2147483648 falls into the range of 32 bit signed integers 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)
?>

This is probably very similar to the MS C bug which also treats -2147483648 as an UNSIGNED because it thinks it's out of the range of a signed int.

The problem is that the parser does not view "-x" as a single token, but rather as two, "-" and "x".  Since "x" is out of the range of an INT, it is promoted to float, even though in this unique case, "-x" is in the range of an int.

The best cure is probably to replace "-2147483648" with "0x80000000", as that is the hexadecimal equivalent of the same number.

Hope that helps explain what's going on

Peace

- Eric / fez
up
-7
autotelic at NOOOOSPAM dot hotmail dot com
6 years ago
A note about converting IP addresses for storage in database.  For MySQL, this is unnecessary as it has built in support via the INET functions.  Also, there is no need to use BIGINT.  UNSIGNED INT is, at 4 bytes, the perfect size for holding an IP (column must be defined as UNSIGNED).  This can basically halve the storage size, as BIGINT is an 8 byte data type.

INET_ATON() converts a dotted IP string to INT:
INSERT table(ip) VALUES(INET_ATON('127.0.0.1'));

INET_NTOA() converts an INT to dotted IP string:
SELECT INET_NTOA(ip) FROM table
returns '127.0.0.1'

Details:
http://dev.mysql.com/doc/refman/5.1/en/miscellaneous-functions.html
up
-7
winterheat
6 years ago
PHP_INT_SIZE seems to be 8 when it is 64 bit integers... so 8 means the number of bytes, or number of 8-bits.
up
-8
sean dot gilbertson at gmail dot com
5 years ago
You can make a signed, negative integer an unsigned integer (in string form) by doing the following:

<?php
$unsigned
= sprintf('%u', -5);

echo
$unsigned; // prints 4294967291
?>
up
-9
php at keith tyler dot com
3 years ago
If you need to convert a numeric string (or more to the point, an object that represents a numeric value) that is greater then PHP_INT_MAX, and you don't have GMP or BCMath installed, you can cast to float.

For example, when using SimpleXMLElement, you sometimes have to cast the extracted values, such as xml attributes, because they are returned as SimpleXMLElements and not their values' native types. While print() has no trouble with converting them, other functions, such as max(), might not.

But if you cast such a value with (int), and it is over PHP_INT_MAX, you will just get PHP_INT_MAX (and vice versa for negative numbers).

The Q&D no-muss solution is to cast to (float) instead.
up
-10
Richard
3 years ago
Integer arithmetic in PHP is more accurate than one might think. On a 32-bit system, the largest value that can be held in an INT is  2147483647.
However, a FLOAT can accurately hold integer values up to 10000000000000.
(this is because the significand precision of a double is 53-bits).
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