CascadiaPHP 2024

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

要使用八进制表达,数字前必须加上 0(零)。 PHP 8.1.0 起,八进制表达也可以在前面加上 0o 或者 0O 。 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

从 PHP 7.4.0 开始,整型数值可能会包含下划线 (_),为了更好的阅读体验,这些下划线在展示的时候,会被 PHP 过滤掉。

示例 #1 整数文字表达

<?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 0o0O 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

hexadecimal : 0[xX][0-9a-fA-F]+(_[0-9a-fA-F]+)*

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

binary      : 0[bB][01]+(_[01]+)*

integer     : decimal
            | hexadecimal
            | octal
            | binary

整型数 int 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 不支持无符号的 intint 值的字长可以用常量 PHP_INT_SIZE来表示, 最大值可以用常量 PHP_INT_MAX 来表示, 最小值可以用常量 PHP_INT_MIN 表示。

整数溢出

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

示例 #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)
?>

示例 #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 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。

<?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 int,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 int 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 int 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。

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 float 转换成整数 int时,将向零取整。自 PHP 8.1.0 起,当将非整数类型的 float 转换为失去精度的 int 时,会发出弃用通知。

<?php

function 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 8
var_dump(foo(8.0)); // 8 in both cases

var_dump((int)8.1); // 8 in both cases
var_dump(intval(8.1)); // 8 in both cases
?>

如果浮点数超出了 int 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 int 结果。 在此情况下没有警告,甚至没有任何通知!

注意:

NaN 和 Infinity 在转换成 int 时是零。

警告

绝不要将未知的分数强制转换为 int,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

如果 string 是 numeric 或者前导数字, 则将它解析为相应的 int 值,否则将转换为零(0)。

NULL 转换

null 会转换为零(0)。

从其它类型转换

警告

没有定义从其它类型转换为 int 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

User Contributed Notes 11 notes

up
136
php at richardneill dot org
11 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
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2
lewismoten at gmail dot com
1 month ago
Regarding the part about `PHP does not support unsigned ints`, this often causes much confusion when using the hard-coded minimum value of a signed integer that matches PHP_INT_MIN.

<?php
// 64-bit example
var_dump(PHP_INT_MIN);
var_dump(-9223372036854775808);
var_dump(PHP_INT_MIN === -9223372036854775808);
// int(-9223372036854775808)
// float(-9.223372036854776E+18)
// bool(false)
?>

Although visually, I've typed the same value that PHP_INT_MIN writes out `-9223372036854775808`, the language parser only understands it as two expressions with a negate operator followed by `9223372036854775808`. The value exceeds the maximum value of an integer by one, and is promoted to a float. Although it's been suggested in the past to wire up a hook to look for this value specifically, it's more difficult than it sounds. The tokenizer is unable to evaluate both the negate and integer as one token. In addition, you would also need to address binary, octal, and hex literals.

<?php
var_dump
(-9223372036854775808); // literal decimal
var_dump(-0x8000000000000000); // literal hex
var_dump(-0b1000000000000000000000000000000000000000000000000000000000000000); // literal binary
var_dump(-01000000000000000000000); // literal octal
?>

If you need to hard-code the minimum value, use `PHP_INT_MIN`. It was introduced specifically for this edge case. Alternative methods are to write `-9223372036854775807 - 1`.
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56
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[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);
?>
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15
ganlvtech at qq dot com
3 years ago
Be aware of float to int cast overflow

<?php

// You may expected these
var_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 these
var_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).
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21
dhairya lakhera
6 years ago
-------------------------------------------------------------------------
Question :
var_dump((int) 010); //Output 8

var_dump((int) "010"); //output 10

First 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");
10
php > var_export(intval("010"));
10
php > var_export(intval("010", 8));
8
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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.
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16
Anonymous
17 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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15
rustamabd@gmail-you-know-what
17 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
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9
Anonymous
9 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
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6
litbai
8 years 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.
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-1
Jacek
17 years ago
On 64 bits machines max integer value is 0x7fffffffffffffff (9 223 372 036 854 775 807).
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