integer 是集合 ? = {..., -2, -1, 0, 1, 2, ...} 中的某个数。
参见：
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)
$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
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，除了 Windows 下 PHP 7 以前的版本，总是 32 位的。
PHP 不支持无符号的 integer。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，最小值可以在 PHP 7.0.0 及以后的版本中用常量 PHP_INT_MIN 表示。
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。
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 #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。
<?php
var_dump(25/7); // float(3.5714285714286)
var_dump((int) (25/7)); // int(3)
var_dump(round(25/7)); // float(4)
?>
要明确地将一个值转换为 integer，用 (int) 或 (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。
将 resource 转换成 integer 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。
FALSE 将产生出 0（零），TRUE 将产生出
1（壹）。
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，除了 Windows，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！
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。
绝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。
参见字符串转换为数值。
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。
$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 :
1000000000000000000000000000000000000000000000000000000000000000
111111111111111111111111111111111111111111111111111110000000000
"There is no integer division operator in PHP". But since PHP 7, there is the intdiv function.
-------------------------------------------------------------------------
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
<?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.
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.
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
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
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).
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.
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
You can make a signed, negative integer an unsigned integer (in string form) by doing the following:
<?php
$unsigned = sprintf('%u', -5);
echo $unsigned; // prints 4294967291
?>
<?php
//This is a simple function to return number of digits of an integer.
//function declaration
function count_digit($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
?>
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!
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
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.
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);
?>
On 64 bits machines max integer value is 0x7fffffffffffffff (9 223 372 036 854 775 807).
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'
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.
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($i/36)*36)."\n";
?>
Will output:
i=6.88713E+009
i%36=-24
alternative i%36=20
Try this one instead:
function iplongtostring($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";
}
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) + $fix / 256 / 256
)
);
}
else {
return('');
}
}
Sometimes you need to parse an unsigned
32 bit integer. Here's a function I 've used:
function parse_unsigned_int($string) {
$x = (float)$string;
if ($x > (float)2147483647)
$x -= (float)"4294967296";
return (int)$x;
}