便携式浮点变量模板 [英] Portable floating point variable templates

问题描述

如何在c ++ 14中定义便携式高精度浮点变量模板？以下程序应使用 double 和 long double 精度打印pi。

How to define portable high-precision floating point variable templates in c++14? The program below should print pi with double and long double precision.

#include <iostream>
#include <iomanip>
#include <limits>

template<typename T>
constexpr T pi = T(3.141592653589793238462643383279502884197);


int main() {
  std::cout << std::setprecision(std::numeric_limits<double>::max_digits10) << pi<double> << std::endl;
  std::cout << std::setprecision(std::numeric_limits<long double>::max_digits10) << pi<long double> << std::endl;
}

$ b < std = c ++ 14 我得到

3.1415926535897931
3.141592653589793116

我的猜测是gcc将数字转换为double，然后应用模板。我不认为 L 文字是答案，因为我不想重写，当我移动到float128或更高。如何使编译器保留所有精度？

My guess is that gcc converts the number to a double and then applies the template. I don't think the L literal is the answer because I don't want to rewrite when I move to float128 or higher. How can I make the compiler retain all the precision?

推荐答案

除非另有说明，否则所有浮点文字的类型为 double 。你使用它作为 T （无论 T 可能）的初始化器无关紧要，将 double 转换为 T 初始化 。

All floating point literals, unless otherwise suffixed, are of type double. That you use it as an initializer for T (whatever T may be) doesn't matter, you're still going to initialize pi with a double converted to a T.

使用 l 后缀字面，使其成为 long double ，然后转换为 T 。

Suffix the literal with l to make it a long double, which is then converted to T.

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