C++数学常数使用笔记

zxl19 2024-04-06

C++
Note

我的C++数学常数使用笔记。

数学常数

使用模板类

C++20引入，使用时需要包含头文件：
```
 #include <numbers>
```
定义的数学常数均在numbers子命名空间中，为了使表示形式简便，本文默认使用std::numbers命名空间：
```
 using namespace std::numbers;
```

原型声明：

 namespace std::numbers {
 template <class T>
 inline constexpr T e_v = /* unspecified */;
 template <class T>
 inline constexpr T log2e_v = /* unspecified */;
 template <class T>
 inline constexpr T log10e_v = /* unspecified */;
 template <class T>
 inline constexpr T pi_v = /* unspecified */;
 template <class T>
 inline constexpr T inv_pi_v = /* unspecified */;
 template <class T>
 inline constexpr T inv_sqrtpi_v = /* unspecified */;
 template <class T>
 inline constexpr T ln2_v = /* unspecified */;
 template <class T>
 inline constexpr T ln10_v = /* unspecified */;
 template <class T>
 inline constexpr T sqrt2_v = /* unspecified */;
 template <class T>
 inline constexpr T sqrt3_v = /* unspecified */;
 template <class T>
 inline constexpr T inv_sqrt3_v = /* unspecified */;
 template <class T>
 inline constexpr T egamma_v = /* unspecified */;
 template <class T>
 inline constexpr T phi_v = /* unspecified */;

 template <floating_point T>
 inline constexpr T e_v<T> = /* see description */;
 template <floating_point T>
 inline constexpr T log2e_v<T> = /* see description */;
 template <floating_point T>
 inline constexpr T log10e_v<T> = /* see description */;
 template <floating_point T>
 inline constexpr T pi_v<T> = /* see description */;
 template <floating_point T>
 inline constexpr T inv_pi_v<T> = /* see description */;
 template <floating_point T>
 inline constexpr T inv_sqrtpi_v<T> = /* see description */;
 template <floating_point T>
 inline constexpr T ln2_v<T> = /* see description */;
 template <floating_point T>
 inline constexpr T ln10_v<T> = /* see description */;
 template <floating_point T>
 inline constexpr T sqrt2_v<T> = /* see description */;
 template <floating_point T>
 inline constexpr T sqrt3_v<T> = /* see description */;
 template <floating_point T>
 inline constexpr T inv_sqrt3_v<T> = /* see description */;
 template <floating_point T>
 inline constexpr T egamma_v<T> = /* see description */;
 template <floating_point T>
 inline constexpr T phi_v<T> = /* see description */;

 inline constexpr double e = e_v<double>;
 inline constexpr double log2e = log2e_v<double>;
 inline constexpr double log10e = log10e_v<double>;
 inline constexpr double pi = pi_v<double>;
 inline constexpr double inv_pi = inv_pi_v<double>;
 inline constexpr double inv_sqrtpi = inv_sqrtpi_v<double>;
 inline constexpr double ln2 = ln2_v<double>;
 inline constexpr double ln10 = ln10_v<double>;
 inline constexpr double sqrt2 = sqrt2_v<double>;
 inline constexpr double sqrt3 = sqrt3_v<double>;
 inline constexpr double inv_sqrt3 = inv_sqrt3_v<double>;
 inline constexpr double egamma = egamma_v<double>;
 inline constexpr double phi = phi_v<double>;
 }  // namespace std::numbers

使用宏定义

使用时需要包含头文件：
```
 #include <cmath>
```

原型声明：

 #if defined __USE_MISC || defined __USE_XOPEN
 #define M_E 2.7182818284590452354         /* e */
 #define M_LOG2E 1.4426950408889634074     /* log_2 e */
 #define M_LOG10E 0.43429448190325182765   /* log_10 e */
 #define M_LN2 0.69314718055994530942      /* log_e 2 */
 #define M_LN10 2.30258509299404568402     /* log_e 10 */
 #define M_PI 3.14159265358979323846       /* pi */
 #define M_PI_2 1.57079632679489661923     /* pi/2 */
 #define M_PI_4 0.78539816339744830962     /* pi/4 */
 #define M_1_PI 0.31830988618379067154     /* 1/pi */
 #define M_2_PI 0.63661977236758134308     /* 2/pi */
 #define M_2_SQRTPI 1.12837916709551257390 /* 2/sqrt(pi) */
 #define M_SQRT2 1.41421356237309504880    /* sqrt(2) */
 #define M_SQRT1_2 0.70710678118654752440  /* 1/sqrt(2) */
 #endif

C++数学常数使用笔记

数学常数

使用模板类

使用宏定义

参考