How to get PI value in C++ without defining it manually?
Hi,
On some platforms, you may need to define _USE_MATH_DEFINES and include the math.h header file to access the value of pi using M_PI. For example:
#define _USE_MATH_DEFINES
#include <math.h>
double circumference = 2 * M_PI * radius;
In newer platforms, you may not need to define _USE_MATH_DEFINES, and M_PI will be available without it. Additionally, some platforms may provide a long double value for pi as a GNU Extension, which can be accessed using M_PIl. For example:
long double area = M_PIl * radius * radius;
Always check your math.h for the specific definitions available on your platform.
Using the M_PI constant from the math.h header is generally a more reliable and convenient approach than manually typing in the value of pi. It ensures accuracy and consistency across platforms.
However, if you prefer to avoid including headers or defines, you can manually define the value of pi in your code. Just be careful to type it accurately to the precision you need, as mistakes can lead to errors in your calculations.
const double PI = 3.141592653589793238463;
const float PI_F = 3.14159265358979f;
While this approach can work, it’s important to note that calculating acos or atan is generally more computationally expensive than using a precalculated value like M_PI.
Since the C++ standard library doesn’t define a constant for PI, you would need to define it yourself or rely on compiler-specific extensions. If portability is not a concern, you can check your compiler’s manual for any specific extensions it might provide for this purpose.
In C++, you can define PI using the atan function as follows:
const double PI = std::atan(1.0) * 4;
However, note that the initialization of this constant is not guaranteed to be static. Some compilers, like G++, handle these math functions as intrinsics and are able to compute this constant expression at compile-time.