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# Integers

An integer is a number of the set Z = {..., -2, -1, 0, 1, 2, ...}.

See also: Arbitrary length integer / GMP, Floating point numbers, and Arbitrary precision / BCMath

## Syntax

Integers can be specified in decimal (10-based), hexadecimal (16-based) or octal (8-based) notation, optionally preceded by a sign (- or +).

If you use the octal notation, you must precede the number with a 0 (zero), to use hexadecimal notation precede the number with 0x.

範例 11-1. 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 possible 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.

警告

If an invalid digit is passed to octal integer (i.e. 8 or 9), the rest of the number is ignored.

範例 11-2. Octal weirdness

`<?php var_dump(01090); // 010 octal = 8 decimal ?>`

## Integer overflow

If you specify a number beyond the bounds of the integer type, it will be interpreted as a float instead. Also, if you perform an operation that results in a number beyond the bounds of the integer type, a float will be returned instead.

`<?php $large_number = 2147483647; var_dump($large_number); // output: int(2147483647) $large_number = 2147483648; var_dump($large_number); // output: float(2147483648) // this goes also for hexadecimal specified integers: var_dump( 0x80000000 ); // output: float(2147483648) $million = 1000000; $large_number = 50000 * $million; var_dump($large_number); // output: float(50000000000) ?>`

警告
Unfortunately, there was a bug in PHP so that this does not always work correctly when there are negative numbers involved. For example: when you do -50000 * $million, the result will be -429496728. However, when both operands are positive there is no problem. This is solved in PHP 4.1.0.

There is no integer division operator in PHP. 1/2 yields the float 0.5. You can cast the value to an integer to always round it downwards, or you can use the round() function.

`<?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 the (integer) cast. However, in most cases you do not need to use the cast, since a value will be automatically converted if an operator, function or control structure requires an integer argument. You can also convert a value to integer with the function intval().

See also type-juggling.

### 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), the result is undefined, since the float hasn't got enough precision to give an exact integer result. No warning, not even a notice will be issued in this case!

警告

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 for more information the warning about float-precision.

### From strings

See String conversion to numbers

### From other types

注意
Behaviour of converting to integer is undefined for other types. Currently, the behaviour is the same as if the value was first converted to boolean. However, do not rely on this behaviour, as it can change without notice.

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