C++ 测试案例

infinity()

#include <iostream>
#include <limits>

int main() {
    double inf = std::numeric_limits<double>::infinity();
    
    std::cout << "Infinity (double): " << inf << std::endl;

    // 可以用来与其他值进行比较
    if (inf > 1000000) {
        std::cout << "Infinity is greater than 1 million!" << std::endl;
    }

    return 0;
}

# g++ testInf.cpp -o testInf
# ./testInf 
Infinity (double): inf
Infinity is greater than 1 million!

nextafter

# cat nextafter.cpp
#include <iostream>
#include <cmath>
#include <limits>
#include <iomanip>

template <typename TNum>
TNum roundToDecimals(TNum number, int decimals) {
    // 计算放大倍数
    long double factor = std::pow(10.0L, static_cast<long double>(decimals));

    // 定义正无穷
    static const TNum kInf = std::numeric_limits<TNum>::infinity();

    // 如果 number 是负数
    if (number < 0) {
        return static_cast<TNum>(std::round(std::nextafter(number, -kInf) * factor) / factor);
    }

    // 如果 number 是正数
    return static_cast<TNum>(std::round(std::nextafter(number, kInf) * factor) / factor);
}

int main() {
    // 测试数据
    double number1 = 194.71512499999997;
    int decimals1 = 5;

    double number2 = -194.71512499999997;
    int decimals2 = 5;

    // 调用四舍五入函数并输出结果
    std::cout << std::setprecision(8) << "Rounded value of " << number1 << " to " << decimals1 << " decimals: "
              << roundToDecimals(number1, decimals1) << std::endl;

    std::cout << std::setprecision(8) << "Rounded value of " << number2 << " to " << decimals2 << " decimals: "
              << roundToDecimals(number2, decimals2) << std::endl;

    return 0;
}

# ./nextafter
Rounded value of 194.71512 to 5 decimals: 194.71513
Rounded value of -194.71512 to 5 decimals: -194.71513

测试 nextafter

        long double factor = std::pow(10.0L, static_cast<long double>(decimals1));
        static const double kInf = std::numeric_limits<double>::infinity();
        std::cout << std::setprecision(15) << "std::nextafter(number, kInf)" << std::nextafter(number1, kInf) << std::endl;

# ./nextafterdebug
std::nextafter(number, kInf)194.715125
Rounded value of 194.71512 to 5 decimals: 194.71513