C++ overloading [duplicate]

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Operator overloading

I would like to overload < and > to alphabetize strings and I'm not sure how to do it.

How do I call the string c开发者_运维问答lass again to redefine < and >?

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You don't need to overload these, as std::string already provides them.

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In general, to overload functions, you don't call a class. You cannot call a class. You can also not add methods to classes. If you want to provide, for instance, operator < for an existing class A, you have to create is as a free function in the namespace of A:

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

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The binary operators greater than (>) and less than (<) operators are mostly used in if statements, so the source code example below is also using if statements. Let's look at the operator overloading source code:

#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;
}

you can inherit Box from String to overload these operators for string