我在std：：optionals的结构中有一个结构，我试图找到结构中的最小值和最大值。然而，使用std：：minmax_element似乎不准确，我不得不拆分比较函数，转而使用std：：min_element和std：：max_element。有没有一种方法可以让我仍然使用std：：minmax_element并且更干净？

#include <iostream>
#include <vector>
#include <optional>
#include <algorithm>

struct AE
{
    double A;
    double E;
};

struct HM
{
   std::optional<AE> H;
   std::optional<AE> M;
};

bool CompareHM(const HM& a_, const HM& b_)
{
    // If both H fields have a value, compare them by A
    if (a_.H.has_value() && b_.H.has_value()) 
    {
        return a_.H->A < b_.H->A;
    }
    // If only one H field has a value, set to false
    else
    {
        return false;
    }
}

bool CompareHMMax(const HM& a_, const HM& b_)
{
    // If both H fields have a value, compare them by A
    if (a_.H.has_value() && b_.H.has_value()) 
    {
        return a_.H->A < b_.H->A;
    }
    // If only one H field has a value, consider it larger
    else if (a_.H.has_value()) 
    {
        return false;
    }
    // If both H fields are empty, or if just b has a value
    else {
        return false;
    }
}

bool CompareHMMin(const HM& a_, const HM& b_)
{
    // If both H fields have a value, compare them by A
    if (a_.H.has_value() && b_.H.has_value()) 
    {
        return a_.H->A < b_.H->A;
    }
    // If only one H field has a value, consider it smaller
    else if (a_.H.has_value()) 
    {
        return true;
    }
    // If both H fields are empty, or if just b has a value
    else 
    {
        return false;
    }
}

int main()
{
    // Create a vector of HM structs with some data
    std::vector<HM> vec = {
        HM{AE{1.8, 4.5}, AE{7.2, 4.1}},
        HM{AE{2.3, 3.4}, std::nullopt},
        HM{std::nullopt, AE{6.7, 8.9}},
        HM{AE{0.9, 2.1}, std::nullopt},
        HM{AE{1.8, 4.2}, AE{7.6, 9.0}},
        HM{std::nullopt, AE{0.7, 13.5}},
        HM{std::nullopt, AE{0.5, 19.3}},
        HM{AE{2.1, 4.2}, std::nullopt},
    };

    auto minmax = std::minmax_element(vec.begin(), vec.end(), CompareHM);
    auto min = std::min_element(vec.begin(), vec.end(), CompareHMMin);
    auto max = std::max_element(vec.begin(), vec.end(), CompareHMMax);

    // Print the results
    std::cout << "Correct Min A value: " << min->H->A << "\n";
    std::cout << "Correct Max A value: " << max->H->A << "\n";
    std::cout << "Incorrect Min A value using minmax_element: " << minmax.first->H->A << "\n";
    std::cout << "Incorrect Max A value using minmax_element: " << minmax.second->H->A << "\n";

    return 0;
}

输出：

Correct Min A value: 0.9
Correct Max A value: 2.3
Incorrect Min A value using minmax_element: 1.8
Incorrect Max A value using minmax_element: 2.1