PHP, 자료형 , 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), 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)
$a = 0b11111111; // binary number (equivalent to 255 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]+

binary      : 0b[01]+

integer     : [+-]?decimal
            | [+-]?hexadecimal
            | [+-]?octal
            | [+-]?binary

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). 64-bit platforms usually have a maximum value of about 9E18, except on Windows prior to PHP 7, where it was always 32 bit. PHP does not support unsigned integers. Integer size can be determined using the constant PHP_INT_SIZE, maximum value using the constant PHP_INT_MAX since PHP 4.4.0 and PHP 5.0.5, and minimum value using the constant PHP_INT_MIN since PHP 7.0.0.

Warning

Prior to PHP 7, if an invalid digit was given in an octal integer (i.e. 8 or 9), the rest of the number was ignored. Since PHP 7, a parse error is emitted.

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 #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 integer division operator in PHP. 1/2 yields the float 0.5. The value can be casted to an integer to round it towards zero, or theround() 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 tointeger with the intval() function.

If a resource is converted to an integer, then the result will be the unique resource number assigned to the resource by PHP at runtime.

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 on 32-bit platforms and +/- 9.22e+18 = 2^63 on 64-bit platforms other than Windows), 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.

<?php
echo (int) ( (0.1+0.7) * 10 ); // echoes 7!
?>

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