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), 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.
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 : [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.
Warning
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.
<?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)?> Warning
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) ?> 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: type-juggling.
From booleans
FALSE will yield 0 (zero), and TRUE will yield 1 (one).
From floating point numbers
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!
Warning
Never cast an unknown fraction to integer, as this can sometimes lead to unexpected results.
<?phpecho (int) ( (0.1+0.7) * 10 ); // echoes 7!?> 