How to use the PI constant in C++
Posted By: Anonymous
I want to use the PI constant and trigonometric functions in some C++ program. I get the trigonometric functions with include <math.h>
. However, there doesn’t seem to be a definition for PI in this header file.
How can I get PI without defining it manually?
Solution
On some (especially older) platforms (see the comments below) you might need to
#define _USE_MATH_DEFINES
and then include the necessary header file:
#include <math.h>
and the value of pi can be accessed via:
M_PI
In my math.h
(2014) it is defined as:
# define M_PI 3.14159265358979323846 /* pi */
but check your math.h
for more. An extract from the “old” math.h
(in 2009):
/* Define _USE_MATH_DEFINES before including math.h to expose these macro
* definitions for common math constants. These are placed under an #ifdef
* since these commonlydefined names are not part of the C/C++ standards.
*/
However:

on newer platforms (at least on my 64 bit Ubuntu 14.04) I do not need to define the
_USE_MATH_DEFINES

On (recent) Linux platforms there are
long double
values too provided as a GNU Extension:# define M_PIl 3.141592653589793238462643383279502884L /* pi */
Answered By: Anonymous
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