## Integer 整型

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

### 语法

Int 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 +）。 可以用负运算符 来表示一个负的 int

`<?php\$a = 1234; // 十进制数\$a = 0123; // 八进制数 (等于十进制 83)\$a = 0o123; // 八进制数 (PHP 8.1.0 起)\$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)\$a = 1_234_567; // 整型数值 (PHP 7.4.0 以后)?>`

int literal 的结构形式从 PHP 8.1.0 开始是（之前不允许使用 `0o``0O` 八进制前缀，并且 PHP 7.4.0 之前不允许使用下划线）：

```decimal     : [1-9][0-9]*(_[0-9]+)*
| 0

octal       : 0[oO]?[0-7]+(_[0-7]+)*

binary      : 0[bB]+(_+)*

integer     : decimal
| octal
| binary
```

### 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)?>`

`<?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 没有 int 除法取整运算符，要使用 intdiv() 实现。 `1/2` 产生出 float `0.5`。 值可以舍弃小数部分，强制转换为 int，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 int 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

`<?phpfunction foo(\$value): int { return \$value; }var_dump(foo(8.1)); // 自 PHP 8.1.0 起：“Deprecated: Implicit conversion from float 8.1 to int loses precision”var_dump(foo(8.1)); // PHP 8.1.0 之前为 8var_dump(foo(8.0)); // 8 in both casesvar_dump((int)8.1); // 8 in both casesvar_dump(intval(8.1)); // 8 in both cases?>`

NaN 和 Infinity 在转换成 int 时是零。

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

#### 从 NULL 转换

`null` 会转换为零（`0`）。

### User Contributed Notes 19 notes

138
php at richardneill dot org
10 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`
52
d_n at NOSPAM dot Loryx dot com
16 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 * 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);?>`
kuzawinski dot marcin_NOSPAM at gmail dot com
3 years ago
`Integer literals may be decimal, octal, hexadecimal or binary, but integer values have single representation;<?phpvar_dump(010); // int(8) NOT int(010) var_dump(0x10); // int(16) NOT int(0x10) var_dump(0b10); // int(2) NOT int(0b10) ?>This is the reason why casting integer to string gives us always a decimal:<?phpvar_dump((string) 010); // string(8) NOT string(010)var_dump((string) 0x10); // string(16) NOT string(0x10)var_dump((string) 0b10); // string(2) NOT string(0b10)?>`
11
ganlvtech at qq dot com
3 years ago
`Be aware of float to int cast overflow<?php// You may expected thesevar_dump(0x7fffffffffffffff); // int(9223372036854775807)var_dump(0x7fffffffffffffff + 1); // float(9.2233720368548E+18)var_dump((int)(0x7fffffffffffffff + 1)); // int(9223372036854775807)var_dump(0x7fffffffffffffff + 1 > 0); // bool(true)var_dump((int)(0x7fffffffffffffff + 1) > 0); // bool(true)var_dump((int)'9223372036854775807'); // int(9223372036854775807)var_dump(9223372036854775808); // float(9.2233720368548E+18)var_dump((int)'9223372036854775808'); // int(9223372036854775807)var_dump((int)9223372036854775808); // int(9223372036854775807)// But actually, it likes thesevar_dump(0x7fffffffffffffff); // int(9223372036854775807)var_dump(0x7fffffffffffffff + 1); // float(9.2233720368548E+18)var_dump((int)(0x7fffffffffffffff + 1)); // int(-9223372036854775808) <-----var_dump(0x7fffffffffffffff + 1 > 0); // bool(true)var_dump((int)(0x7fffffffffffffff + 1) > 0); // bool(false) <-----var_dump((int)'9223372036854775807'); // int(9223372036854775807)var_dump(9223372036854775808); // float(9.2233720368548E+18)var_dump((int)'9223372036854775808'); // int(9223372036854775807)var_dump((int)9223372036854775808); // int(-9223372036854775808) <-----?>These overflows are dangerous when you try to compare it with zero, or substract it from another value (e.g. money).`
23
dhairya lakhera
6 years ago
`-------------------------------------------------------------------------Question : var_dump((int) 010); //Output 8var_dump((int) "010"); //output 10First one is octal notation so the output is correct. But what about the when converting "010" to integer. it should be also output 8 ?--------------------------------------------------------------------------Answer :Casting to an integer using (int) will always cast to the default base, which is 10.Casting a string to a number this way does not take into account the many ways of formatting an integer value in PHP (leading zero for base 8, leading "0x" for base 16, leading "0b" for base 2). It will simply look at the first characters in a string and convert them to a base 10 integer. Leading zeroes will be stripped off because they have no meaning in numerical values, so you will end up with the decimal value 10 for (int)"010".Converting an integer value between bases using (int)010 will take into account the various ways of formatting an integer. A leading zero like in 010 means the number is in octal notation, using (int)010 will convert it to the decimal value 8 in base 10.This is similar to how you use 0x10 to write in hexadecimal (base 16) notation. Using (int)0x10 will convert that to the base 10 decimal value 16, whereas using (int)"0x10" will end up with the decimal value 0: since the "x" is not a numerical value, anything after that will be ignored.If you want to interpret the string "010" as an octal value, you need to instruct PHP to do so. intval("010", 8) will interpret the number in base 8 instead of the default base 10, and you will end up with the decimal value 8. You could also use octdec("010") to convert the octal string to the decimal value 8. Another option is to use base_convert("010", 8, 10) to explicitly convert the number "010" from base 8 to base 10, however this function will return the string "8" instead of the integer 8.Casting a string to an integer follows the same the logic used by the intval function:Returns the integer value of var, using the specified base for the conversion (the default is base 10).intval allows specifying a different base as the second argument, whereas a straight cast operation does not, so using (int) will always treat a string as being in base 10.php > var_export((int) "010");10php > var_export(intval("010"));10php > var_export(intval("010", 8));8`
18
egwayjen at gmail dot com
6 years ago
`"There is no integer division operator in PHP". But since PHP 7, there is the intdiv function.`
14
Anonymous
8 years 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`
litbai
7 years ago
`<?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.`
17
rustamabd@gmail-you-know-what
16 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`
14
Anonymous
16 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'`
10
Anonymous
19 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; }`
Jacek
16 years ago
`On 64 bits machines max integer value is 0x7fffffffffffffff (9 223 372 036 854 775 807).`
darkshire
16 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 * 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.`
-6
eric
15 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`
-12
pere dot cil at wanadoo dot fr
12 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`
-10
13453814063 at 163 dot com
5 years ago
`\$e = 0x8000000000000000;\$e2 = 0b1000000000000000000000000000000000000000000000000000000000000000;if (\$e == \$e2){ echo "e==e2<br>";}else{ echo "e!=e2<br>";}pirnt "e!=e2"----------------------------echo decbin(\$e) . "<br>";echo decbin(\$e2) . "<br>";the result is :1000000000000000000000000000000000000000000000000000000000000000111111111111111111111111111111111111111111111111111110000000000`
-18
wbcarts at juno dot com
15 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!`
-14
dewi at dewimorgan dot com
8 years 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.`
-25
jmw254 at cornell dot edu
17 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";}` 