Integer integer type

Integer integer type

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

See:

Arbitrary length integer/GMP

Floating point type

Arbitrary precision math library/BCMath

Syntax

Integer values ​​can use decimal, hexadecimal base, octal Or binary representation, preceded by an optional symbol (- or +).

Binary representation of integer is available since PHP 5.4.0.

To use octal expression, 0 (zero) must be added before the number. To use hexadecimal expression, the number must be preceded by 0x. To use binary representation, 0b must be added before the number.

Example #1 Integer literal expression

<?php
$a = 1234; // 十进制数
$a = -123; // 负数
$a = 0123; // 八进制数 (等于十进制 83)
$a = 0x1A; // 十六进制数 (等于十进制 26)
?>

The formal description of integer is:

decimal : [1-9][0-9]*
| 0

hexadecimal : 0[xX][0-9a-fA-F]+

octal : 0[0-7]+

binary : 0b[01]+

integer : [+-]?decimal
| [+- ]?hexadecimal
                                                                                                                                                                                                     hexadecimal . The maximum value on a 64-bit platform is usually around 9E18. PHP does not support unsigned integers. The word length of the Integer value can be represented by the constant PHP_INT_SIZE. Since PHP 4.4.0 and PHP 5.0.5, the maximum value can be represented by the constant PHP_INT_MAX.

If an illegal number (i.e. 8 or 9) is passed to an octal number, the remaining digits will be ignored.

Example #2 Strange things about octal numbers

<?php
var_dump(01090); // 八进制 010 = 十进制 8
?>

Integer overflow

If a given number exceeds the range of integer , it will be interpreted as float. Similarly, if the result of the operation exceeds the range of integer, float will be returned.

Example #3 Integer overflow under 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 #4 64 位系统下的整数溢出
<?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 float 0.5. The value can be cast to an integer, discarding the fractional part, or using the round() function for better rounding.

<?php
var_dump(25/7);         // float(3.5714285714286)
var_dump((int) (25/7)); // int(3)
var_dump(round(25/7));  // float(4)
?>

Convert to integer

To explicitly convert a value to an integer, cast with (int) or (integer) . In most cases, however, casting is not necessary because when an operator, function, or flow control requires an integer parameter, the value is automatically converted. You can also use the function intval() to convert a value into an integer.

See: Discrimination of type conversion.

Converting from a Boolean value

FALSE will produce 0 (zero), TRUE will produce 1 (one).

Converting from Float

When converting from a floating point number to an integer, it will be rounded down.

If the floating point number exceeds the integer range (usually +/- 2.15e+9 = 2^31 on 32-bit platforms, +/- 9.22e+18 = 2^63 on 64-bit platforms), The result is undefined because there is insufficient precision to give an exact integer result. There is no warning in this case, not even any notification!

Never cast an unknown fraction to an integer, as this can sometimes lead to unpredictable results.

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

See warning about floating point precision.

Convert from string

See Convert string to numeric value.

Converting from other types

Caution

There is no defined behavior for converting from other types to integer. Do not rely on any existing behavior as it may change without notice.