C++11标准模板（STL）- 常用数学函数 - 浮点数操作函数 - 检查第一个浮点参数是否小于或等于第二个（std::islessequal）

常用数学函数

检查第一个浮点参数是否小于或等于第二个

std::islessequal

定义于头文件 <math.h>
#define islessequal(x, y) /* implementation defined */		(C99 起)

确定浮点数 x 是否小于或等于浮点数 y ，而不设置浮点异常。

参数

x	-	浮点值
y	-	浮点值

返回值

若 x <= y 则为非零整数值，否则为 ​0​ 。

注意

若一或两个参数为 NaN ，则内建的 operator<= 对浮点数可能引发 FE_INVALID 。此宏是 operator<= 的“安静”版本。

调用示例

#include <iostream>
#include <cstdlib>
#include <typeinfo>
#include <cinttypes>
#include <cmath>
#include <math.h>
#include <tgmath.h>

int main()
{
    std::cout << std::boolalpha;

    //确定浮点数 x 是否小于或等于浮点数 y ，而不设置浮点异常。
    for (int i = 0; i <= 10; i += 1)
    {
        const float fNumber = std::acos(-1) / 2 / i;
        const float fNumber1 = std::acos(fNumber) - i / 10;
        const float fNumber2 = std::asin(fNumber) + i / 10;
        std::cout << "std::islessequal(" << fNumber1
                  << "," << fNumber2 << "):   "
                  << std::islessequal(fNumber1, fNumber2) << std::endl;
    }
    std::cout << std::endl;

    for (int i = 0; i <= 10; i += 1)
    {
        const float fNumber = std::cos(-1) / 2 / i;
        const float fNumber1 = std::cos(fNumber) - i / 10;
        const float fNumber2 = std::sin(fNumber) + i / 10;
        std::cout << "std::islessequal(" << fNumber1
                  << "," << fNumber2 << "):   "
                  << std::islessequal(fNumber1, fNumber2) << std::endl;
    }
    std::cout << std::endl;

    for (int i = 0; i <= 10; i += 1)
    {
        const float fNumber = std::tan(i);
        const float fNumber1 = std::cos(fNumber) - i / 10;
        const float fNumber2 = std::sin(fNumber) + i / 10;
        std::cout << "std::islessequal(" << fNumber1
                  << "," << fNumber2 << "):   "
                  << std::islessequal(fNumber1, fNumber2) << std::endl;
    }

    return 0;
}

输出

std::islessequal(nan,nan):   false
std::islessequal(nan,nan):   false
std::islessequal(0.667457,0.903339):   true
std::islessequal(1.01973,0.55107):   false
std::islessequal(1.16723,0.403565):   false
std::islessequal(1.25123,0.319571):   false
std::islessequal(1.30591,0.264886):   false
std::islessequal(1.34447,0.226327):   false
std::islessequal(1.37316,0.197634):   false
std::islessequal(1.39536,0.175431):   false
std::islessequal(0.413063,1.15773):   true

std::islessequal(nan,nan):   false
std::islessequal(0.963731,0.266877):   false
std::islessequal(0.990891,0.134665):   false
std::islessequal(0.995948,0.0899287):   false
std::islessequal(0.99772,0.0674865):   false
std::islessequal(0.998541,0.0540039):   false
std::islessequal(0.998987,0.04501):   false
std::islessequal(0.999255,0.0385834):   false
std::islessequal(0.99943,0.0337625):   false
std::islessequal(0.99955,0.0300123):   false
std::islessequal(-0.0003649,1.02701):   true

std::islessequal(1,0):   false
std::islessequal(0.0133882,0.99991):   true
std::islessequal(-0.57634,-0.81721):   false
std::islessequal(0.989857,-0.142064):   false
std::islessequal(0.401336,0.915931):   true
std::islessequal(-0.971594,0.236656):   true
std::islessequal(0.957956,-0.286916):   false
std::islessequal(0.643719,0.765262):   true
std::islessequal(0.86954,-0.493862):   false
std::islessequal(0.899437,-0.43705):   false
std::islessequal(-0.202925,1.60388):   true

原文地址：https://blog.csdn.net/qq_40788199/article/details/143636372

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