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Integers

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

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.

Beispiel #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.

Warnung

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

Beispiel #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)
?>

Warnung

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.

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 doesn't have enough precision to give an exact integer result. No warning, not even a notice will be issued when this happens!

Warnung

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

See String conversion to numbers

From other types

Achtung

The behaviour of converting to integer is undefined for other types. Do not rely on any observed behaviour, as it can change without notice.