Integer 整型

一个 integer 是集合 ℤ = {..., -2, -1, 0, 1, 2, ...} 中的一个数。

参见:

语法

整型值可以使用十进制,十六进制,八进制或二进制表示,前面可以加上可选的符号(- 或者 +)。

二进制表达的 integer 自 PHP 5.4.0 起可用。

要使用八进制表达,数字前必须加上 0(零)。要使用十六进制表达,数字前必须加上 0x。要使用二进制表达,数字前必须加上 0b

Example #1 整数文字表达

<?php
$a 
1234// 十进制数
$a = -123// 负数
$a 0123// 八进制数 (等于十进制 83)
$a 0x1A// 十六进制数 (等于十进制 26)
?>

integer 语法的结构形式是:

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

整型数的字长和平台有关,尽管通常最大值是大约二十亿(32 位有符号)。64 位平台下的最大值通常是大约 9E18。PHP 不支持无符号整数。Integer 值的字长可以用常量 PHP_INT_SIZE来表示,自 PHP 4.4.0 和 PHP 5.0.5后,最大值可以用常量 PHP_INT_MAX 来表示。

Warning

如果向八进制数传递了一个非法数字(即 8 或 9),则后面其余数字会被忽略。

Example #2 八进制数的怪事

<?php
var_dump
(01090); // 八进制 010 = 十进制 8
?>

整数溢出

如果给定的一个数超出了 integer 的范围,将会被解释为 float。同样如果执行的运算结果超出了 integer 范围,也会返回 float

Example #3 32 位系统下的整数溢出

<?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)
?>

Example #4 64 位系统下的整数溢出

<?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 中没有整除的运算符。1/2 产生出 float 0.5。值可以舍弃小数部分强制转换为 integer,或者使用 round() 函数可以更好地进行四舍五入。

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

转换为整型

要明确地将一个值转换为 integer,用 (int)(integer) 强制转换。不过大多数情况下都不需要强制转换,因为当运算符,函数或流程控制需要一个 integer 参数时,值会自动转换。还可以通过函数 intval() 来将一个值转换成整型。

参见:类型转换的判别

布尔值转换

FALSE 将产生出 0(零),TRUE 将产生出 1(壹)。

浮点型转换

当从浮点数转换成整数时,将向下取整。

如果浮点数超出了整数范围(32 位平台下通常为 +/- 2.15e+9 = 2^31,64 位平台下通常为 +/- 9.22e+18 = 2^63),则结果为未定义,因为没有足够的精度给出一个确切的整数结果。在此情况下没有警告,甚至没有任何通知!

Warning

决不要将未知的分数强制转换为 integer,这样有时会导致不可预料的结果。

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

参见关于浮点数精度的警告

从字符串转换

参见字符串转换为数值

从其它类型转换

Caution

没有定义从其它类型转换为整型的行为。不要依赖任何现有的行为,因为它会未加通知地改变。

add a note add a note

User Contributed Notes 23 notes

up
44
Paul
7 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
18
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
10
d_n at NOSPAM dot Loryx dot com
7 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
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
Hamza Burak Ylmaz
6 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
?>
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1
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
1
darkshire
7 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
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'
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-2
Kalimuthu Aruchamy
2 months ago
<?php
echo "<br>".(int) ( (0.1+0.7) * 10 ); // echoes 7. Wrong. I think this is bug in PHP. It works fine for below expressions
echo "<br>".(int) ( (0.2+0.7) * 10 ); // echoes 9. Right
echo "<br>".(int) ( (0.3+0.7) * 10 ); // echoes 10. Right
echo "<br>".(int) ( (0.4+0.7) * 10 ); // echoes 11. Right
?>
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-1
Jacek
7 years ago
On 64 bits machines max integer value is 0x7fffffffffffffff (9 223 372 036 854 775 807).
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.
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-2
wbcarts at juno dot com
6 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
-4
iletras at yahoo dot com
4 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
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
-6
jmw254 at cornell dot edu
8 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
-6
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
-3
Alex
9 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
-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
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
-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.
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-10
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
-12
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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