pow
(PHP 4, PHP 5)
pow — 指数表达式
说明
$base
, number $exp
)
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 with integer type,
otherwise it will be returned as a float .
更新日志
| 版本 | 说明 |
|---|---|
| 4.2.0 |
如果不能计算幂，将发出一条警告， pow() 将返回 FALSE 。 pow() 开始不产生任何的警告。
|
| 4.0.6 | 如果可能函数现在会返回 integer 的结果，之前 总是返回 float ，For older versions, you may receive a bogus result for complex numbers. |
范例
Example #1 pow() 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() - 任意精度数字的成方
- gmp_pow() - Raise number into power
用户评论:
[#1] scott at arciszewski dot me [2014-02-14 15:24:39]
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);
?>
[#2] chris at ocportal dot com [2012-05-21 16:05:11]
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.
[#3] gilthansREMOVEME at gmail dot com [2006-12-15 07:50:29]
Note that pow(0, 0) equals to 1 although mathematically this is undefined.