pow()

(PHP 4, PHP 5, PHP 7)

指数表达式

说明

pow(number$base,number$exp):number

返回$base的$exp次方的幂。如果可能，本函数会返回integer。

参数

$base

The base to use

$exp

指数

返回值

$base的$exp次方的幂。 If both arguments are non-negative integers and the result can be represented as an integer, the result will be returned withintegertype, otherwise it will be returned as afloat.

更新日志

范例

Example #1pow()的一些例子

<?php
var_dump(pow(2, 8)); // int(256)
echo pow(-1, 20); // 1
echo pow(0, 0); // 1
echo pow(-1, 5.5); // PHP >4.0.6  NAN
echo pow(-1, 5.5); // PHP <=4.0.6 1.#IND
?>

注释

Note:

本函数会转换所有输入为数字，即使是非标量值，会导致怪异的（weird）结果。

参见

• exp() 计算 e 的指数
• sqrt() 平方根
• bcpow() 任意精度数字的乘方
• gmp_pow()Raise number into power

Many notations use "^" as a power operator, but in PHP (and other C-based languages) that is actually the XOR operator. You need to use this 'pow' function, there is no power operator.
i.e. 3^2 means "3 XOR 2" not "3 squared".
It is particular confusing as when doing Pythagoras theorem in a 'closet points' algorithm using "^" you get results that look vaguely correct but with an error.

Note that pow(0, 0) equals to 1 although mathematically this is undefined.

It is official now that you could use 
<?php
2 ** 3; // 8
// instead of
pow(2, 3); // 8
?>

As of PHP 5.6.0alpha2, there is now an exponentiation operator. If this is kept in the final release, it may be worth noting here.
<?php
// These two will be equivalent as of PHP 5.6.0
$x = $y ** 2;
$x = pow($y, 2);
?>

funny thing
number_format(pow(2, 1023));
gives a long number
but number_format(pow(2, 1024));
gives inf