## Integer 整型

integer 是集合 ? = {..., -2, -1, 0, 1, 2, ...} 中的某个数。

### 语法

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)\$a = 0b11111111; // 二进制数字 (等于十进制 255)?> ```

integer 语法的结构形式是：

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

octal       : 0[0-7]+

binary      : 0b+

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

Warning

PHP 7 以前的版本里，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。PHP 7 以后，会产生 Parse Error。

### 整数溢出

Example #2 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 #3 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。

``` <?phpvar_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

resource 转换成 integer 时， 结果会是 PHP 运行时为 resource 分配的唯一资源号。

#### 从布尔值转换

`FALSE` 将产生出 0（零），`TRUE` 将产生出 1（壹）。

#### 从浮点型转换

Note:

PHP 7.0.0 起，NaN 和 Infinity 在转换成 integer 时，不再是 undefined 或者依赖于平台，而是都会变成零。

Warning

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

Caution

### User Contributed Notes

litbai 25-Feb-2016 05:26
``` <?php \$ipArr = explode('.', \$ipString); \$ipVal = (\$ipArr << 24)        + (\$ipArr << 16)        + (\$ipArr << 8)        + \$ipArr         ; ?> 1. the priority of bit op is lower than '+',so there should be brackets. 2. there is no unsighed int in PHP, if you use 32 bit version，the code above will get negative result when the first position of IP string greater than 127. 3. what the code actually do is calculate the integer value of transformed 32 binary bit from IP string. ```
dewi at dewimorgan dot com 10-May-2015 04:41
``` Note that the soft-typing of numbers in PHP means that some things become very difficult. For example, efficiently emulating the more common linear congruential generators (LCGs) for fast, deterministic, pseudo-randomness. The naive code to create the next value in a sequence (for power-of-2 values of \$m) is: \$seed = (\$seed * \$a + \$c) % \$m; ...where \$m, \$a, and \$c are values and data types carefully chosen such that repeating this operation will eventually generate every value in the range \$0 to \$m, with no repetition. I can find no good commonly used LCGs which use PHP-compatible values. The LCG values used in by rand() in systems like Borland Delphi, Virtual Pascal, MS Visual/Quick C/C++, VMS's MTH\$RANDOM, old versions of glibc, Numerical Recipes, glibc, GCC, ANSI C, Watcom, Digital Mars, CodeWarrior, IBM VisualAge C/C++, java.util.Random, Newlib, MMX... *all* fail when ported, for one of two reasons, and sometimes both:  - In PHP on 32 bit machines and all Windows machines, \$m = 2^32 or larger requires UInt or even UInt64, or the result becomes negative. - Large \$a multiplied by an integer seed gets converted to a float64, but the number can be too long for the 53-bit mantissa, and it drops the least significant digits... but the LCG code above requires that the most significant digits should be lost. These are two classes of problem to beware of when porting integer math to PHP,  and I see no clean and efficient way to avoid either one. So if designing a cross-platform system that must work in PHP, you must select LCG values that fit the following criteria: \$m = 2^31 or less (PHP limitation). Recommend: 2^31. \$a = Less than 2^22 (PHP limitation); \$a-1 divisible by all prime factors of \$m; \$a-1 divisible by 4 if \$m is. Recommend: 1+(4*(any prime <= 1048573)). \$c = smaller than (2^53-(\$m*\$a)) (PHP limitation); relatively prime with \$m. Recommend: any prime <= 23622320123. ```
Anonymous 09-Jan-2015 06:31
``` Converting to an integer works only if the input begins with a number (int) "5txt" // will output the integer 5 (int) "before5txt" // will output the integer 0 (int) "53txt" // will output the integer 53 (int) "53txt534text" // will output the integer 53 ```
php at richardneill dot org 01-Mar-2013 03:25
``` 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 ```
Richard 17-Apr-2011 06:53
``` 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). ```
php at keith tyler dot com 13-Apr-2011 08:08
``` 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. ```
pere dot cil at wanadoo dot fr 15-Mar-2011 10:59
``` 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 ```
sean dot gilbertson at gmail dot com 08-Jan-2009 10:57
``` 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 ?> ```
Hamza Burak Ylmaz 24-Oct-2008 11:36
``` <?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 ?> ```
wbcarts at juno dot com 07-Oct-2008 03:25
``` 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! ```
eric 11-Jun-2008 10:50
``` 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 ```
darkshire 16-Nov-2007 01:56
``` 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 * 0x1000000             + \$ipArr * 0x10000             + \$ipArr * 0x100             + \$ipArr             ; ?> This can be written in a bit more efficient way: <?php   \$ipArr    = explode('.',\$_SERVER['REMOTE_ADDR']);   \$ip       = \$ipArr<<24             + \$ipArr<<16             + \$ipArr <<8             + \$ipArr             ; ?> shift is more cheaper. ```
d_n at NOSPAM dot Loryx dot com 13-Aug-2007 02:33
``` 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 * 0x1000000             + \$ipArr * 0x10000             + \$ipArr * 0x100             + \$ipArr             ; ?> 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 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*0x1000000); // for clarity         \$ipArr = (\$ipVint & 0xFF0000)  >> 16;         \$ipArr = (\$ipVint & 0xFF00  )  >> 8;         \$ipArr =  \$ipVint & 0xFF;         \$ipDotted = implode('.', \$ipArr); ?> ```
Jacek 10-Mar-2007 01:51
``` On 64 bits machines max integer value is 0x7fffffffffffffff (9 223 372 036 854 775 807). ```
09-Mar-2007 04:26
``` 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 03:50
``` 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 10:42
``` 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 07:14
``` 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 10:15
``` 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 07:18
``` 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;     } ```