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
Un número entero (o integer) es un número del conjunto ℤ = {..., -2, -1, 0, 1, 2, ...}.
Véase también:
Los integer pueden especificarse mediante notación decimal (base 10), hexadecimal (base 16), octal (base 8) o binaria (base 2), opcionalmente precedidos por un signo (- o +).
Los literales de tipo integer binarios están disponibles desde PHP 5.4.0.
Para utilizar la notación octal, se antepone al número un 0 (cero).
Para utilizar la notación hexadecimal, se antepone al número 0x.
Para utilizar la notación binaria, se antepone al número 0b.
Ejemplo #1 Literales de números enteros
<?php
$a = 1234; // número decimal
$a = -123; // un número negativo
$a = 0123; // número octal (equivale a 83 decimal)
$a = 0x1A; // número hexadecimal (equivale a 26 decimal)
$a = 0b11111111; // número binario (equivale al 255 decimal)
?>
Formalmente, la estructura de los literales de tipo integer es:
decimal : [1-9][0-9]*
| 0
hexadecimal : 0[xX][0-9a-fA-F]+
octal : 0[0-7]+
binario : 0b[01]+
entero : [+-]?decimal
| [+-]?hexadecimal
| [+-]?octal
| [+-]?binario
El tamaño de un integer depende de la plataforma, aunque el valor usual
es un valor máximo de aproximadamente dos mil millones (esto es, 32 bits con signo).
Las plataformas de 64 bits normalmente tienen un valor máximo de aproximadamente 9E18, excepto en
Windows antes de PHP 7, que siempre es de 32 bits. PHP no tiene soporte para el tipo
integer sin signo. El tamaño de un integer se puede determinar
mediante la constante PHP_INT_SIZE, y el valor máximo mediante la
constante PHP_INT_MAX desde PHP 4.4.0 y PHP 5.0.5,
y el valor mínimo mediante la constante PHP_INT_MIN desde
PHP 7.0.0.
Antes de PHP 7, si a un integer octal se le proporcionaba un dígito no válido (esto es, 8 o 9), se ignoraba el resto del número. Desde PHP 7, se emite un error de análisis.
Si PHP encuentra un número fuera de los límites de un integer, se interpretará en su lugar como un valor de tipo float. También, una operación cuyo resultado sea un número fuera de los límites de un integer devolverá en su lugar un valor de tipo float.
Ejemplo #2 Desbordamiento de enteros en sistemas de 32 bit
<?php
$número_grande = 2147483647;
var_dump($número_grande); // int(2147483647)
$número_grande = 2147483648;
var_dump($número_grande); // float(2147483648)
$millón = 1000000;
$número_grande = 50000 * $millón;
var_dump($número_grande); // float(50000000000)
?>
Ejemplo #3 Desbordamiento de enteros en sistemas de 64 bit
<?php
$número_grande = 9223372036854775807;
var_dump($número_grande); // int(9223372036854775807)
$número_grande = 9223372036854775808;
var_dump($número_grande); // float(9.2233720368548E+18)
$millón = 1000000;
$número_grande = 50000000000000 * $millón;
var_dump($número_grande); // float(5.0E+19)
?>
No existe el operador de división de integer en PHP.
1/2 produce el float 0.5.
El valor puede ser convertido a un integer redondeándolo a cero, o
mediante la función round() que permite un mayor control sobre el redondeo.
<?php
var_dump(25/7); // float(3.5714285714286)
var_dump((int) (25/7)); // int(3)
var_dump(round(25/7)); // float(4)
?>
Para convertir explícitamente un valor al tipo integer se puede emplear
tanto (int) como (integer). Sin embargo,
la mayoría de las veces la conversión no es necesaria, ya que un valor es convertido
de forma automática cuando un operador, función o estructura de control requiera un
argumento de tipo integer. Un valor también puede ser convertido al
tipo integer mediante la función intval().
Si un resource es convertido a un integer, el resultado será el número de recurso único asignado al resource por PHP durante la ejecución.
Consulte también la Manipulación de tipos.
false producirá 0 (cero), y true producirá
1 (uno).
Cuando se convierte un float a un integer, el número será redondeado hacia cero.
Si el valor de tipo float esta por debajo de los límites de un integer (normalmente
+/- 2.15e+9 = 2^31 en plataformas de 32 bits y
+/- 9.22e+18 = 2^63 en plataformas de 64 bits distintas de
Windows), el resultado es indefinido, debido a que float no tiene
la precisión suficiente para ofrecer el resultado como un integer exacto.
No se mostrará ninguna advertencia, ni siquiera un aviso, cuando esto ocurra.
Nota:
A partir de PHP 7.0.0,0, en lugar de ser indefinidos y dependientes de la plataforma, NaN e Infinity siempre serán cero al amoldarlos a integer.
Nunca se debe convertir una fracción desconocida a un integer, ya que a veces puede conducir a resultados inesperados.
<?php
echo (int) ( (0.1+0.7) * 10 ); // ¡muestra 7!
?>
Consulte también la advertencia sobre la precisión de float
Consulte Conversión de string a números
El comportamiento de la conversión de integer a otros tipos es indefinido. No confíe en ningún comportamiento observado, ya que puede cambiar sin previo aviso.
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
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);
?>
-------------------------------------------------------------------------
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
"There is no integer division operator in PHP". But since PHP 7, there is the intdiv function.
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).
Integer literals may be decimal, octal, hexadecimal or binary, but integer values have single representation;
<?php
var_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:
<?php
var_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)
?>
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
<?php
$ipArr = explode('.', $ipString);
$ipVal = ($ipArr[0] << 24)
+ ($ipArr[1] << 16)
+ ($ipArr[2] << 8)
+ $ipArr[3]
;
?>
1. the priority of bit op is lower than '+',so there should be brackets.
2. there is no unsighed int in PHP, if you use 32 bit version，the code above will get negative result when the first position of IP string greater than 127.
3. what the code actually do is calculate the integer value of transformed 32 binary bit from IP string.
Converting to an integer works only if the input begins with a number
(int) "5txt" // will output the integer 5
(int) "before5txt" // will output the integer 0
(int) "53txt" // will output the integer 53
(int) "53txt534text" // will output the integer 53
To force the correct usage of 32-bit unsigned integer in some functions, just add '+0' just before processing them.
for example
echo(dechex("2724838310"));
will print '7FFFFFFF'
but it should print 'A269BBA6'
When adding '+0' php will handle the 32bit unsigned integer
correctly
echo(dechex("2724838310"+0));
will print 'A269BBA6'
Sometimes you need to parse an unsigned
32 bit integer. Here's a function I 've used:
function parse_unsigned_int($string) {
$x = (float)$string;
if ($x > (float)2147483647)
$x -= (float)"4294967296";
return (int)$x;
}
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.
On 64 bits machines max integer value is 0x7fffffffffffffff (9 223 372 036 854 775 807).
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
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
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!
$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
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 $m. Recommend: any prime <= 23622320123.
Try this one instead:
function iplongtostring($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";
}