Parse PHP data type integer (Integer)

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

Syntax

Integer values ​​can be represented in decimal, hexadecimal, octal or binary, and can be preceded by an optional symbol (- or +).

Binary expressed integer is available since PHP 5.4.0.

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

Example #1 IntegerText 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
| [+-]?octal
| [+-]? binary

The word size of integers is platform-dependent, although the usual maximum is about two billion (32-bit signed). The maximum value on 64-bit platforms is usually about 9E18. PHP does not support unsigned integers. The word length of an 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.

Warning

If an illegal number is passed to an octal number (i.e. 8 or 9), 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 Integer overflow under 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 float 0.5. The value can be discarded with the decimal part cast to an integer, or use 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, use (int) or (integer) cast. 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 to an integer type.

See: Discrimination of type conversion.

Converting from Boolean values

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

Converting from Floating

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 under the 32-bit platform, usually +/- 9.22e+18 = 2^63 under the 64-bit platform) , 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!

Warning

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!
?>

The behavior of converting from other types to integer is not defined. Do not rely on any existing behavior as it may change without notice.

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