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Integers
An integer is a number of the set ℤ = {..., 2, 1, 0, 1, 2, ...}.
See also:
Syntax
Integers can be specified in decimal (base 10), hexadecimal (base 16), octal (base 8) or binary (base 2) notation, optionally preceded by a sign ( or +).
Binary integer literals are available since PHP 5.4.0.
To use octal notation, precede the number with a 0 (zero). To use hexadecimal notation precede the number with 0x. To use binary notation precede the number with 0b.
Example #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 : [19][09]*  0 hexadecimal : 0[xX][09afAF]+ octal : 0[07]+ binary : 0b[01]+ integer : [+]?decimal  [+]?hexadecimal  [+]?octal  [+]?binary
The size of an integer is platformdependent, although
a maximum
value of about two billion is the usual value (that's 32 bits signed).
64bit platforms usually have a maximum value of about 9E18. 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.
Example #2 Octal weirdness
<?php
var_dump(01090); // 010 octal = 8 decimal
?>
Integer overflow
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.
Example #3 Integer overflow on a 32bit 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 #4 Integer overflow on a 64bit 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 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)
?>
Converting to integer
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: typejuggling.
From booleans
FALSE
will yield 0 (zero), and TRUE
will yield
1 (one).
From floating point numbers
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 on 32bit platforms and +/ 9.22e+18 = 2^63 on 64bit platforms), 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.
From strings
From other types
The behaviour of converting to integer is undefined for other types. Do not rely on any observed behaviour, as it can change without notice.