如何在C++中比较两个不同的联合

#include <iostream>

union UnionA {
    int num;
    char ch;
};

union UnionB {
    float f;
    double d;
};

bool operator==(const UnionA& a, const UnionA& b) {
    return a.num == b.num;
}

bool operator<(const UnionB& a, const UnionB& b) {
    return a.d < b.d;
}

int main() {
    UnionA a1, a2;
    a1.num = 10;
    a2.num = 20;

    if (a1 == a2) {
        std::cout << "a1 is equal to a2" << std::endl;
    } else {
        std::cout << "a1 is not equal to a2" << std::endl;
    }

    UnionB b1, b2;
    b1.d = 3.14;
    b2.d = 2.71;

    if (b1 < b2) {
        std::cout << "b1 is less than b2" << std::endl;
    } else {
        std::cout << "b1 is not less than b2" << std::endl;
    }

    return 0;
}