C++超载

Question

可能的重复：
运算符重载

我想重载<和>按字母顺序排列字符串，我不知道该怎么做。

如何再次调用字符串类来重新定义<和>？

Answer 1

您不需要重载它们，因为 std::string 已经提供了它们。

---

一般来说，要重载函数，您不会调用类。你不能调用一个类。您也不能向类添加方法。例如，如果您想为现有类 A 提供 operator <，则必须在 A< 的命名空间中将 is 创建为自由函数/代码>：

bool operator<(const A& left, const B& right) {
    // implement logic here
}

Answer 2

二元运算符大于（>）和小于（<）运算符主要用于if语句中，因此下面的源代码示例也使用if语句。我们看一下运算符重载源码：

#include<iostream>
using namespace std;

class Box {
    public:
        Box(double boxLength, double boxWidth, double boxHeight)
            :length(boxLength), width(boxWidth), height(boxHeight) {}

        // Compute the volume of a box.
        double volume() const {
            return length*width*height;
        }

        // First inline function
        inline bool operator<(const Box& someBox) const {
            return volume() < someBox.volume();
        }

        // Second inline function
        inline bool operator<(const double someValue) const {
            return volume() < someValue;
        }

        // Third inline function
        inline bool operator>(const Box& someBox) const {
            return volume() > someBox.volume();
        }

        // Fourth inline function
        inline bool operator>(const double someValue) const {
            return volume() > someValue;
        }

    private:
        double length;
        double width;
        double height;
};

int main() {
    Box myBox(15.0, 10.0, 5.0);
    Box myBox2(15.0, 5.0, 5.0);

    cout << "The myBox volume is: " << myBox.volume() << "\n";
    cout << "The myBox2 volume is: " << myBox2.volume() << "\n";

    // Trying the less than binary operator
    if(myBox < myBox2) {
        cout << "The myBox volume is less than myBox2 volume!\n";
    }else{
        cout << "The myBox volume is not less than myBox2 volume!\n";
    }

    // Trying the less than binary operator
    if(myBox < 1000) {
        cout << "The myBox volume is less than 1000!\n";
    }else{
        cout << "The myBox volume is not less than 1000!\n";
    }

    // Trying the greater than binary operator
    if(myBox > myBox2) {
        cout << "The myBox volume is greater than myBox2 volume!\n";
    }else{
        cout << "The myBox volume is not greater than myBox2 volume!\n";
    }

    // Trying the greater than binary operator
    if(myBox > 500) {
        cout << "The myBox volume is greater than 500!\n";
    }else{
        cout << "The myBox volume is not greater than 500!\n";
    }

    return 0;
}

可以从String继承Box来为字符串重载这些运算符