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
An int is a number of the set ℤ = {..., -2, -1, 0, 1, 2, ...}.
Ints can be specified in decimal (base 10), hexadecimal (base 16), octal (base 8) or binary (base 2) notation. The negation operator can be used to denote a negative int.
To use octal notation, precede the number with a 0 (zero).
As of PHP 8.1.0, octal notation can also be preceded with 0o or 0O.
To use hexadecimal notation precede the number with 0x.
To use binary notation precede the number with 0b.
As of PHP 7.4.0, integer literals may contain underscores (_) between digits,
for better readability of literals. These underscores are removed by PHP's scanner.
Example #1 Integer literals
<?php
$a = 1234; // decimal number
$a = 0123; // octal number (equivalent to 83 decimal)
$a = 0o123; // octal number (as of PHP 8.1.0)
$a = 0x1A; // hexadecimal number (equivalent to 26 decimal)
$a = 0b11111111; // binary number (equivalent to 255 decimal)
$a = 1_234_567; // decimal number (as of PHP 7.4.0)
?>
Formally, the structure for int literals is as of PHP 8.1.0
(previously, the 0o or 0O octal
prefixes were not allowed, and prior to PHP 7.4.0 the underscores were
not allowed):
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
The size of an int is platform-dependent, although a maximum
value of about two billion is the usual value (that's 32 bits signed).
64-bit platforms usually have a maximum value of about 9E18.
PHP does not support unsigned ints.
int size can be determined
using the constant PHP_INT_SIZE, maximum value using
the constant PHP_INT_MAX,
and minimum value using the constant PHP_INT_MIN.
If PHP encounters a number beyond the bounds of the int type, it will be interpreted as a float instead. Also, an operation which results in a number beyond the bounds of the int type will return a float instead.
Example #2 Integer overflow on a 32-bit system
<?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 Integer overflow on a 64-bit system
<?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)
?>
There is no int division operator in PHP, to achieve this
use the intdiv() function.
1/2 yields the float 0.5.
The value can be cast to an int to round it towards zero, 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 int, 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
int argument. A value can also be converted to
int with the intval() function.
If a resource is converted to an int, then the result will be the unique resource number assigned to the resource by PHP at runtime.
See also Type Juggling.
When converting from float to int, the number will be rounded towards zero. As of PHP 8.1.0, a deprecation notice is emitted when implicitly converting a non-integral float to int which loses precision.
<?php
function foo($value): int {
return $value;
}
var_dump(foo(8.1)); // "Deprecated: Implicit conversion from float 8.1 to int loses precision" as of PHP 8.1.0
var_dump(foo(8.1)); // 8 prior to PHP 8.1.0
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
?>
If the float is beyond the boundaries of int (usually
+/- 2.15e+9 = 2^31 on 32-bit platforms and
+/- 9.22e+18 = 2^63 on 64-bit platforms),
the result is undefined, since the float doesn't
have enough precision to give an exact int result.
No warning, not even a notice will be issued when this happens!
Note:
NaN and Infinity will always be zero when cast to int.
Never cast an unknown fraction to int, 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.
If the string is
numeric
or leading numeric then it will resolve to the
corresponding integer value, otherwise it is converted to zero
(0).
The behaviour of converting to int is undefined for other types. Do not rely on any observed behaviour, as it can change without notice.
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 // 123Regarding 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`.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);
?>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).-------------------------------------------------------------------------
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.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 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=20Converting 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<?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.