The 4th Annual China PHP Conference

## Integers

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

### Syntax

Integers can be specified in decimal (base 10), hexadecimal (base 16), or octal (base 8) notation, optionally preceded by a sign (- or +).

To use octal notation, precede the number with a 0 (zero). To use hexadecimal notation precede the number with 0x.

Example #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 structure for integer literals is:

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

octal       : 0[0-7]+

integer     : [+-]?decimal
| [+-]?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). 64-bit platforms usually have a maximum value of about 9E18. PHP does not support unsigned integers. Integer size can be determined using the constant PHP_INT_SIZE, and maximum value using the constant PHP_INT_MAX since PHP 4.4.0 and PHP 5.0.5.

Warning

If an invalid digit is given in an octal integer (i.e. 8 or 9), the rest of the number is ignored.

Example #2 Octal weirdness

``` <?phpvar_dump(01090); // 010 octal = 8 decimal?> ```

### Integer overflow

If PHP encounters a number beyond the bounds of the integer type, it will be interpreted as a float instead. Also, an operation which results in a number beyond the bounds of the integer type will return a float instead.

Example #3 Integer overflow on a 32-bit system

``` <?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 Integer overflow on a 64-bit system

``` <?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)?> ```

There is no integer division operator in PHP. 1/2 yields the float 0.5. The value can be casted to an integer to round it downwards, or the round() function provides finer control over rounding.

``` <?phpvar_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 (integer) casts. However, in most cases the cast is not needed, since a value will be automatically converted if an operator, function or control structure requires an integer argument. A value can also be converted to integer with the intval() function.

#### 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 on 32-bit platforms and +/- 9.22e+18 = 2^63 on 64-bit platforms), the result is undefined, since the float doesn't have enough precision to give an exact integer result. No warning, not even a notice will be issued when this happens!

Warning

Never cast an unknown fraction to integer, as this can sometimes lead to unexpected results.

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

#### From other types

Caution

The behaviour of converting to integer is undefined for other types. Do not rely on any observed behaviour, as it can change without notice.

### User Contributed Notes 24 notes

29
d_n at NOSPAM dot Loryx dot com
8 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);?> ```
18
php at richardneill dot org
3 years 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 ```
20
rustamabd@gmail-you-know-what
9 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+009i%36=-24alternative i%36=20 ```
Anonymous
1 year ago
``` 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 ```
11
darkshire
8 years ago
``` d_n at NOSPAM dot Loryx dot com13-Aug-2007 05:33Here 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. ```
litbai
3 months ago
``` <?php\$ipArr = explode('.', \$ipString);\$ipVal = (\$ipArr[0] << 24)       + (\$ipArr[1] << 16)       + (\$ipArr[2] << 8)       + \$ipArr[3]        ;?>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. ```
Anonymous
9 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 integercorrectlyecho(dechex("2724838310"+0));will print 'A269BBA6' ```
-1
Jacek
9 years ago
``` On 64 bits machines max integer value is 0x7fffffffffffffff (9 223 372 036 854 775 807). ```
-1
Anonymous
12 years ago
``` Sometimes you need to parse an unsigned32 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;    } ```
-2
wbcarts at juno dot com
7 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_totalecho 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_totalecho 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! ```
-5
pere dot cil at wanadoo dot fr
5 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:0x5468792130ABCDEFechoes to:6.0822444802213E+18 (cast to float)On a fully 64 bits system, it echoes to:6082244480221302255 ```
-5
rickard_cedergren at yahoo dot com
11 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('');      }   } ```
-5
popefelix at gmail dot com
9 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:<?phperror_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 DateNotice: Object of class Date could not be converted to int in /home/kpeters/work/sketches/ObjectSketch.php on line 7\$date is now 1int(1)\$foo is an instance of fooNotice: Object of class foo could not be converted to int in /home/kpeters/work/sketches/ObjectSketch.php on line 13\$foo is now 1int(1)This is because the objects are first converted to boolean before being converted to int. ```
-2
dewi at dewimorgan dot com
1 year ago
``` 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. ```
-9
eric
7 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 onPeace - Eric / fez ```
-10
jmw254 at cornell dot edu
9 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";} ```
-10
Hamza Burak Ylmaz
7 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 ?> ```
-10
iletras at yahoo dot com
5 years ago
``` //This is a (simpler ?) function to return number of digits of an integer.//function declarationfunction 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 ```
-10
autotelic at NOOOOSPAM dot hotmail dot com
8 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 tablereturns '127.0.0.1'Details:http://dev.mysql.com/doc/refman/5.1/en/miscellaneous-functions.html ```
-10
php at keith tyler dot com
5 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. ```
-11
winterheat
7 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. ```
-8
Alex
2 years 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:<?phpecho (int)(function_exists('imagecreatetruecolor'));?>so i see 0 or 1 in output ```
-15
sean dot gilbertson at gmail dot com
7 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?> ```
-20
Richard
5 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). ```