c++ class function overloading, 연산자(operator) 임의 지정

연산자 operator, function overloading은 매우 중요하다.

특히 operator는 stl과 결합하여 아주 강력한 코딩을 만들 수 있다.

#include <iostream>
#include <string>
#include <vector>
 
class Cat
{
public:
    Cat(std::string name, int age) : mName{ std::move(name) }, mAge{ age } {};
    
    const std::string& name() const
    {
        return mName;
    };
 
    int age() const
    {
        return mAge;
    };
 
    void print(std::ostream& os) const
    {
        os << mName << " " << mAge << std::endl;
    };
 
private:
    std::string mName;
    int mAge;
};
 
bool operator==(const Cat& lhs, const Cat& rhs)
{
    return lhs.age() == rhs.age() && lhs.name() == rhs.name();
}
 
bool operator<(const Cat& lhs, const Cat& rhs)
{
    if (lhs.age() < rhs.age())
    {
        return true;
 
    }
    else
        return false;
 
    return lhs.age() == rhs.age() && lhs.name() == rhs.name();
}
 
std::ostream& operator<<(std::ostream& os, const Cat& c)
{
    return os << c.name() << c.age();
}
 
struct complexNum
{
    double real;
    double imag;
 
    complexNum(double r, double i) : real{ r }, imag{ i } {};
    void print() const
    {
        std::cout << real << " " << imag << "i" << std::endl;
    }
 
 
 
};
complexNum operator+(const complexNum& lhs, const complexNum& rhs)
{
    complexNum c{ lhs.real + rhs.real, lhs.imag + rhs.imag };
    return c;
}
 
int main()
{
    complexNum c1{ 1,1 };
    complexNum c2{ 1,2 };
 
    complexNum c{ c1 + c2 };
    c.print();
 
    Cat kitty{ "kitty", 1 };
    Cat nabi{ "nabi", 2 };
 
    if (kitty == nabi)
    {
        std::cout << "They are same" << std::endl;
        
    }
    else
    {
        std::cout << "They are different!" << std::endl;
    }
    
    if (kitty < nabi) std::cout << "nabi is older" << std::endl;
    else    std::cout << "kitty is older" << std::endl;
    kitty.print(std::cout);
    nabi.print(std::cout);
 
    // std::ostream& operator로 구현
    std::cout << kitty << std::endl;
    std::cout << nabi << std::endl;
    return 0;
}