상속

//--- 기준 클래스 쉐이프
class CShape
  {
protected:
   int       m_type;                   // 쉐이프 유형
   int       m_xpos;                   // X - 기준점 좌표
   int       m_ypos;                   // Y - 기준점 좌표
public:
             CShape(){m_type=0; m_xpos=0; m_ypos=0;} // constructor
   void      SetXPos(int x){m_xpos=x;} // set X
   void      SetYPos(int y){m_ypos=y;} // set Y
  };

//--- 파생 클래스 원
class CCircle : public CShape        // 콜론 뒤에 기준 클래스를 정의합니다
  {                                    // 상속할 수 있는
private:
   int             m_radius;           // 원 반지름
 
public:
                   CCircle(){m_type=1;}// 구성자, type 1 
  };

//--- 파생 클래스 Square
class CSquare : public CShape        // 콜론 뒤에 기준 클래스를 정의합니다
  {                                    // 상속할 수 있는
private:
   int            m_square_side;       // 사각형 면
 
public:
                  CSquare(){m_type=2;} // 구성자, type 2 
  };

class class_name : 
          (public | protected | private) opt  base_class_name
  {                                    
   클래스 멤버 선언
  };

#property copyright "Copyright 2000-2024, MetaQuotes Ltd."
#property link      "https://www.mql5.com"
#property version   "1.00"
//+------------------------------------------------------------------+
//| 몇가지 액세스 유형이 있는 클래스 예제                            |
//+------------------------------------------------------------------+
class CBaseClass
  {
private:             //--- 파생 클래스에서 프라이빗 멤버를 사용할 수 없습니다
   int               m_member;
protected:           //--- 보호된 메서드는 기준 클래스와 파생 클래스에서 사용할 수 있습니다
   int               Member(){return(m_member);}
public:              //--- 클래스 생성자는 모든 클래스 멤버가 사용할 수 있습니다
                     CBaseClass(){m_member=5;return;};
private:             //--- m_member에 값을 할당하는 비공개 방법
   void              Member(int value) { m_member=value;};
 
  };
//+------------------------------------------------------------------+
//| 오류가 있는 파생 클래스                                        |
//+------------------------------------------------------------------+
class CDerived: public CBaseClass // 기본값이므로 공용 상속의 지정을 생략할 수 있습니다
  {
public:
   void Func() // 파생 클래스에서 기준 클래스 멤버에 대한 호출을 포함하는 함수를 정의합니다
     {
      //--- 기준 클래스의 프라이빗 멤버 수정 시도
      m_member=0;        // 오류, 기준 클래스의 프라이빗 멤버를 사용할 수 없습니다
      Member(0);         // 오류, 기준 클래스의 전용 메서드를 파생 클래스에서 사용할 수 없습니다
      //--- 기준 클래스의 멤버 읽기
      Print(m_member);   // 오류, 기준 클래스의 프라이빗 멤버를 사용할 수 없습니다
      Print(Member());   // 오류 없음, 보호된 메서드를 기준 클래스와 해당 파생 클래스에서 사용할 수 있습니다
    }
  };

//+------------------------------------------------------------------+
//| 몇가지 액세스 유형이 있는 클래스 예제                            |
//+------------------------------------------------------------------+
class CBaseMathClass
  {
private:             //--- 파생 클래스에서 프라이빗 멤버를 사용할 수 없습니다
   double            m_Pi;
public:              //--- m_Pi 값 가져오기 및 설정
   void              SetPI(double v){m_Pi=v;return;};
   double            GetPI(){return m_Pi;};
public:              // 클래스 생성자는 모든 멤버가 사용할 수 있습니다
                     CBaseMathClass() {SetPI(3.14);  PrintFormat("%s",__FUNCTION__);};
  };
//+------------------------------------------------------------------+
//| Derived class, in which m_Pi cannot be modified                  |
//+------------------------------------------------------------------+
class CProtectedChildClass: protected CBaseMathClass // 보호 상속
  {
private:
   double            m_radius;
public:              //--- 파생 클래스의 공용 메서드
   void              SetRadius(double r){m_radius=r; return;};
   double            GetCircleLength(){return GetPI()*m_radius;};
  };
//+------------------------------------------------------------------+
//| 스크립트 시작 함수                                         |
//+------------------------------------------------------------------+
void OnStart()
  {
//--- 파생 클래스를 만들 때 기준 클래스의 생성자가 자동으로 호출됩니다
   CProtectedChildClass pt;
//--- 반지름 입력
   pt.SetRadius(10);
   PrintFormat("Length=%G",pt.GetCircleLength());
//--- 아래 라인에 대한 설명을 해제하면 SetPI()가 보호되므로 컴파일 단계에서 오류가 발생합니다
// pt.SetPI(3); 
 
//--- 이제 기준 클래스의 변수를 선언하고 Pi 상수를 10으로 설정해 보십시오
   CBaseMathClass bc;
   bc.SetPI(10);
//--- 여기 결과가 있습니다
   PrintFormat("bc.GetPI()=%G",bc.GetPI());
  }