Integer

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Integer

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 also 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.

Structure

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

Example:

<?php

$a = 1510; // decimal number

$a = -151; // 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)

?>

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 5.0.5, and minimum value using the constant PHP_INT_MIN since PHP 7.0.0.

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 : Overflow on 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 : Overflow on 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 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)

?>

To Integer Conversion

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. 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.

From Boolean

FALSE will yield 0 (zero), and TRUE will yield 1 (one).

From float literals

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!

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!

?>

Note:

As of PHP 7.0.0, instead of being undefined and platform-dependent, NaN and Infinity will always be zero when cast to integer.

From String

When a string is evaluated in a numeric context, the resulting value and type are determined as follows.

If the string does not contain any of the characters '.', 'e', or 'E' and the numeric value fits into integer type limits (as defined by PHP_INT_MAX), the string will be evaluated as an integer. In all other cases it will be evaluated as a float.

The value is given by the initial portion of the string. If the string starts with valid numeric data, this will be the value used. Otherwise, the value will be 0 (zero). Valid numeric data is an optional sign, followed by one or more digits (optionally containing a decimal point), followed by an optional exponent. The exponent is an 'e' or 'E' followed by one or more digits.

<?php

$foo = 1 + "10.5";                // $foo is float (11.5)

$foo = 1 + "-1.3e3";              // $foo is float (-1299)

$foo = 1 + "bob-1.3e3";           // $foo is integer (1)

$foo = 1 + "bob3";                // $foo is integer (1)

$foo = 1 + "10 Small Pigs";       // $foo is integer (11)

$foo = 4 + "10.2 Little Piggies"; // $foo is float (14.2)

$foo = "10.0 pigs " + 1;          // $foo is float (11)

$foo = "10.0 pigs " + 1.0;        // $foo is float (11)     

?>

From other types

Do not rely on any observed behavior, as it can change without notice.