pi

(PHP 4, PHP 5)

pi — 得到圆周率值

说明

float pi ( void )

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。

Example #1 pi()


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

返回值

The value of pi as float.

范例

Example #2 pi() example


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

PHP手册 - N: 得到圆周率值

用户评论:

CCoke at incode dot exportforce dot com (25-Jul-2011 04:31)

i believe the precision (independent of the .ini configuration) is limited by the maximum amout of digits you float type can handle.. maybe it also depends on wheter u use a 32 or 64 bit mashine

ghostt dot ew at gmail dot com (10-Feb-2010 12:05)

The highest current precision you can get from pi() at this point is 49 digits. <?php $precision = 49; ini_set("precision", $precision); echo pi(); //will output 3.141592653589793115997963468544185161590576171875 ?>

gmail user robkohr (05-Dec-2008 11:38)

<?php /* Returns angle of line segment in degrees. Angle will be a positive value between 0 and 360. 0 will be north, 90 east, 180 south, 270 west Author: Robert Kohr */ function get_angle($x1, $y1, $x2, $y2, $negative_y_is_up=0){ //differences in x and y $x = $x2 - $x1; $y = $y2 - $y1; //y will need to be negated for where + y is down if($negative_y_is_up){ //useful in some applications $y = -$y; } return (rad2deg(atan2($x, $y))+360)%360; } ?>

Keamos at gmail (14-Jan-2006 05:31)

For anyone wondering, the highest precision you can get for pi() or M_PI is 20 places after the decimal point, or 3.14159265358979323846.

davidduke at hotmail dot com (28-Mar-2004 02:18)

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)