pi()

(PHP 4, PHP 5, PHP 7)

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 #1pi()例子

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

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)

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