Diese Seite bei php.net
The PHP manual text and comments are covered by the Creative Commons Attribution 3.0 License © the PHP Documentation Group - Impressum - mail("TO:Reinhard Neidl",...)
An integer is a number of the set Z = {..., -2, -1, 0, 1, 2, ...}.
See also:
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.
Beispiel #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
hexadecimal : 0[xX][0-9a-fA-F]+
octal : 0[0-7]+
integer : [+-]?decimal
| [+-]?hexadecimal
| [+-]?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). 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.
If an invalid digit is given in an octal integer (i.e. 8 or 9), the rest of the number is ignored.
Beispiel #2 Octal weirdness
<?php
var_dump(01090); // 010 octal = 8 decimal
?>
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.
<?php
$large_number = 2147483647;
var_dump($large_number);
// output: int(2147483647)
$large_number = 2147483648;
var_dump($large_number);
// output: float(2147483648)
// it's true also for hexadecimal specified integers between 2^31 and 2^32-1:
var_dump( 0xffffffff );
// output: float(4294967295)
// this doesn't go for hexadecimal specified integers above 2^32-1:
var_dump( 0x100000000 );
// output: int(2147483647)
$million = 1000000;
$large_number = 50000 * $million;
var_dump($large_number);
// output: float(50000000000)
?>
Unfortunately, there was a bug in PHP which caused this to not always work correctly when negative numbers were involved. For example, the result of -50000 * $million is -429496728. However, when both operands were positive, there was no problem.
This was fixed in PHP 4.1.0.
There is no integer division operator in PHP. 1/2 yields the float 0.5. The value can be casted to an integer to round it downwards, or the round() function provides finer control over rounding.
<?php
var_dump(25/7); // float(3.5714285714286)
var_dump((int) (25/7)); // int(3)
var_dump(round(25/7)); // float(4)
?>
To explicitly convert a value to integer, use either the (int) or (integer) casts. However, in most cases the cast is not needed, since a value will be automatically converted if an operator, function or control structure requires an integer argument. A value can also be converted to integer with the intval() function.
See also: type-juggling.
FALSE will yield 0 (zero), and TRUE will yield 1 (one).
When converting from float to integer, the number will be rounded towards zero.
If the float is beyond the boundaries of integer (usually +/- 2.15e+9 = 2^31), the result is undefined, since the float doesn't have enough precision to give an exact integer result. No warning, not even a notice will be issued when this happens!
Never cast an unknown fraction to integer, as this can sometimes lead to unexpected results.
<?php
echo (int) ( (0.1+0.7) * 10 ); // echoes 7!
?>
See also the warning about float precision.
The behaviour of converting to integer is undefined for other types. Do not rely on any observed behaviour, as it can change without notice.
//This is a (simpler ?) function to return number of digits of an integer.
//function declaration
function count_digit($number) {
return strlen((string) $number);
}
//function call
$num = 12312;
$number_of_digits = count_digit($num); //this is call :)
echo $number_of_digits;
//prints 5
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
?>
why not just using logarithms?
$num_of_digits = (int)(log($num,$base) +1);
I think this should be more performant (as it relies on the math coprocessor) and it could be extended to number of digits representing the number in any base, not just decimal
<?php
//This is a simple function to return number of digits of an integer.
//function declaration
function count_digit($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!
be careful relying on PHP's data type handling. I have a class that handles database calls and in there a function to handle types and formatting them for insertion.
<?php
case constants::int:
$returnString = ($valueString >= 0) ? $valueString : "null";
break;
?>
Will evaluate to false if a user enters "0" since PHP thinks that the 0 is a Boolean. The following code fixes it:
<?php
case constants::int:
$returnString = ((int)$valueString >= 0) ? (int)$valueString : "null";
break;
?>
Be very careful with code that relies on integer overflow. Negative overflow is handled differently on different platforms. For example, this code:
<?php
echo (int)-3000000000; // a 32bit negative overflow
?>
... outputs 1294967296 on Windows, and -2147483648 on FreeBSD.
(Tested with php 5.2.6, freebsd 7.0)
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
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.
Don't forget about the integer minimum value. From my experimentation, the lowest valid integer is (PHP_INT_MAX * -1)-1. All values smaller than this fail the is_int() test, even though the may appear to act normally during mathematic operations. More info on this: http://www.ebrueggeman.com/blog/php/integers-and-floating-numbers/
When handling very large numbers in PHP, you'll notice they get cut off at hexadecimal 7FFFF FFFF. Sometimes, you don't need to use these numbers in an actual calculation in PHP (i.e. just editing and displaying), and just need to save them in a database.
In that case, you can let MySQL handle the conversion from and to hexadecimal notation. In the example below, engineers need to save hexadecimal addresses up to FFFF FFFF. To update such a value in MySQL, use the following query, where 'addr' is a column with type unsigned integer(10).
<?php
$query = "
UPDATE hardware_register
SET name = ?,
type = ?,
addr = conv(?, 16, 10)
WHERE id = ?
";
?>
And selecting:
<?php
$query = "
SELECT name, type, conv(addr, 10, 16)
FROM hardware_register
WHERE id = ?
";
?>
Note that you'll have to treat the resulting addr column as a string everywhere in PHP. You can't do conversions like:
<?php
$addr_decimal = sprintf("%X", $addr_column);
?>
because that'll result in $addr_decimal having the cut-off, maximum int value.
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 table
returns '127.0.0.1'
Details:
http://dev.mysql.com/doc/refman/5.1/en/miscellaneous-functions.html
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.
"always round it downwards"
It seems to truncate, or round toward zero, rather than downward. If the float is negative, it is rounded up.
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);
?>
This note applies to machines that are using a 32 bit integer size. I imagine the same results occur in 64 bit machines as well (with the number 2^63-1).
-2147483648 falls into the range of 32 bit signed integers (0b10000000000000000000000000000000), 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)
?>
Regards
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;
}
Diese Seite bei php.net