pow

(PHP 4, PHP 5)

pow — 指数表达式

说明

number pow ( number $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() - Raise an arbitrary precision number to another
gmp_pow() - Raise number into power

用户评论:

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.

gilthansREMOVEME at gmail dot com (2006-12-15 07:50:29)

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