pi

(PHP 4, PHP 5, PHP 7)

pi — 得到圆周率值

说明

pi ( void ) : float

返回圆周率的近似值。返回值的 float 精度是由 php.ini 中的 precision 指令确定。默认值是 14。你也可以使用 M_PI 常量，该常量产生与 pi() 完全相同的结果。

返回值

圆周率（pi）的浮点近似值。

范例

Example #1 pi() 例子


<?php
echo pi(); // 3.1415926535898
echo M_PI; // 3.1415926535898
?>

User Contributed Notes

nabikaz at gmail dot com 16-Oct-2018 11:33


alternate:



$pi = 4 * atan(1); // 3.1415926535898

davidduke at hotmail dot com 27-Mar-2004 06:18


Pi is often usefull in con/sin/tan functions..


There are also other Pi related constants.


These are most of them:





M_PI  = 3.14159265358979323846 // pi





// The following were added in PHP 4.0.0


M_PI_2 = 1.57079632679489661923 // pi/2 


M_PI_4 = 0.78539816339744830962 // pi/4 


M_1_PI = 0.31830988618379067154 // 1/pi 


M_2_PI = 0.63661977236758134308 // 2/pi 


M_SQRTPI = 1.77245385090551602729 // sqrt(pi) (Only in PHP 4.0.2+)


M_2_SQRTPI = 1.12837916709551257390 // 2/sqrt(pi)