double、long double、float和float128的比较?
为什么double、long double、float没有区别?
Why is there no difference between double, long double or float?
比如C++中pi的计算是，
#include <iostream>
#include <quadmath.h>
#include <math.h>
int main()
{
float PI0 = acos(-1.0);
double PI1 = acos(-1.0);
long double PI2= acos(-1.0L);
__float128 x = acos(-1.0);
char buf[128];
quadmath_snprintf (buf, sizeof buf, "%*.34Qf",10, x);
std::cout << "Float=" << PI0 << std::endl;
std::cout << "Double=" << PI1 << std::endl;
std::cout << "LongDouble=" << PI2 << std::endl;
std::cout << "Float128=" << buf << std::endl;
}
在终端中:
g++ -std=c++14 FileName.cpp -Wall -pedantic -lquadmath && ./a.out
输出:
Float=3.14159
Double=3.14159
LongDouble=3.14159
Float128=3.1415926535897931159979634685441852
详情:https://msdn.microsoft.com/en-我们/图书馆/cc953fe1.aspx
推荐答案
我的平台没有 __float128，但这里有一个例子，显示了 float、double 和 long double 的精度输出:
My platform does not have a __float128, but here's an example showing output by precision with float, double, and long double:
#include <cmath>
#include <iomanip>
#include <iostream>
#include <limits>
int main()
{
float PI0 = std::acos(-1.0F);
double PI1 = std::acos(-1.0);
long double PI2 = std::acos(-1.0L);
constexpr auto PI0_max_digits10 = std::numeric_limits<decltype(PI0)>::max_digits10;
constexpr auto PI1_max_digits10 = std::numeric_limits<decltype(PI1)>::max_digits10;
constexpr auto PI2_max_digits10 = std::numeric_limits<decltype(PI2)>::max_digits10;
std::cout << "Float=" << std::setprecision(PI0_max_digits10) << PI0 << std::endl;
std::cout << "Double=" << std::setprecision(PI1_max_digits10) << PI1 << std::endl;
std::cout << "LongDouble=" << std::setprecision(PI2_max_digits10) << PI2 << std::endl;
}
相关文章