C++ 상속과 패딩

상속과 패딩

• 일반적인 구조체와 마찬가지로 패딩이 끼게 된다.

  • 패딩이 없는 예제 (int, float)

    #include <iostream>
    
    class Mother
    {
      int i_;
    
    public:
      Mother(const int & i_in = 0)
        : i_(i_in)
      {
        std::cout << "Mother construction\n";
      }
    };
    
    class Child : public Mother
    {
      float d_;
    
    public:
      Child()
        : d_(1.0), Mother(1024)
      {
        std::cout << "Child construction\n";
      }
    };
    
    int        main()
    {
      using namespace std;
    
      cout << sizeof(Mother) << endl;
      cout << sizeof(Child) << endl;
    }
    
    /* stdout
    4
    8
    */

  • 4바이트 패딩 예제 (int, double)

    #include <iostream>
    
    class Mother
    {
      int i_;
    
    public:
      Mother(const int & i_in = 0)
        : i_(i_in)
      {
        std::cout << "Mother construction\n";
      }
    };
    
    class Child : public Mother
    {
      double d_;
    
    public:
      Child()
        : d_(1.0), Mother(1024)
      {
        std::cout << "Child construction\n";
      }
    };
    
    int        main()
    {
      using namespace std;
    
      cout << sizeof(Mother) << endl;
      cout << sizeof(Child) << endl;
    }
    
    /* stdout
    4
    16
    */

  • 끝에 패딩이 4바이트 더 붙은 예제 (int, double, int)

    #include <iostream>
    
    class Mother
    {
      int i_;
    
    public:
      Mother(const int & i_in = 0)
        : i_(i_in)
      {
        std::cout << "Mother construction\n";
      }
    };
    
    class Child : public Mother
    {
      double d_;
      int    tmp_;
    
    public:
      Child()
        : d_(1.0), Mother(1024)
      {
        std::cout << "Child construction\n";
      }
    };
    
    int        main()
    {
      using namespace std;
    
      cout << sizeof(Mother) << endl;
      cout << sizeof(Child) << endl;
    }
    
    /* stdout
    4
    24
    */