C++ 비교 연산자 오버로딩 (Comparison Operator Overloading)

비교 연산자 오버로딩 (Comparison Operator Overloading)

• if문, std::sort 등을 사용하려면 필수적으로 구현해야 한다.

---

예제

• ==, != 오버로딩 예제

  #include <iostream>
  
  class Cents
  {
    int    cents_;
  
  public:
    Cents(int cents = 0) { cents_ = cents; }
  
    bool operator == (Cents& c)
    {
      return (cents_ == c.cents_);
    }
  
    bool operator != (Cents& c)
    {
      return (cents_ != c.cents_);
    }
  
    friend std::ostream& operator << (std::ostream& out, const Cents& cents)
    {
      out << cents.cents_;
      return (out);
    }
  };
  
  int        main()
  {
    using namespace std;
  
    Cents    c1{ 6 };
    Cents    c2{ 6 };
    Cents    c3{ 0 };
  
    cout << std::boolalpha;
    cout << (c1 == c2) << endl;
    cout << (c1 != c2) << endl;
    cout << (c1 == c3) << endl;
    cout << (c1 != c3) << endl;
  }
  
  /* stdout
  true
  false
  false
  true
  */

• < 오버로딩 예제

  • std::sort 함수를 사용하려면 < 연산자를 오버로딩해야 한다.

  #include <iostream>
  #include <vector>
  #include <algorithm>
  
  class Cents
  {
    int    cents_;
  
  public:
    Cents(int cents = 0) { cents_ = cents; }
    int& getCents() { return cents_; }
  
    bool    operator < (const Cents& c)
    {
      return (cents_ < c.cents_);
    }
  
    friend std::ostream& operator << (std::ostream& out, const Cents& cents)
    {
      out << cents.cents_;
      return (out);
    }
  };
  
  int        main()
  {
    using namespace std;
  
    vector<Cents>    arr(20);
  
    for (size_t i = 0; i < 20; ++i)
      arr[i].getCents() = i;
  
    std::random_shuffle(begin(arr), end(arr));
  
    for (auto& e : arr)
      cout << e << ' ';
    cout << endl;
  
    std::sort(begin(arr), end(arr));
  
    for (auto& e : arr)
      cout << e << ' ';
    cout << endl;
  }
  
  /* stdout
  12 1 9 2 0 11 7 19 4 15 18 5 14 13 10 16 6 3 8 17
  0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
  */