详解C++ 中的三种继承方式

class A
{
private:
 int m_data1;
 void print1() { cout << "private print1" << endl; }
protected:
 int m_data2;
 void print2() { cout << "protected print2" << endl; }
public:
 A(int x = 1, int y = 2, int z = 3) : m_data1(x), m_data2(y), m_data3(z) {}
 int m_data3;
 void print3() { cout << "protected print3" << endl; }
};

class B : public A
{
public:
 void test_public() {
  cout << m_data3 << endl;
  print3();
 }
 void test_protected() {
  cout << m_data2 << endl;
  print2();
 }
 void test_private() {
  // 下面两行编译不过，B类内无法访问父类的私有成员
  // cout << m_data1 << endl; 
  // print1();
 }
};


int main(int argc, char const* argv[])
{
 B b;
 b.test_public();
 b.test_protected();
 b.test_private();
 cout << b.m_data3 << endl;
 // cout << b.m_data2 << endl; // 编译不过，子类对象无法访问父类protected的成员
 // cout << b.m_data1 << endl; // 编译不过，子类对象无法访问父类private的成员
 return 0;
}

class A
{
private:
 int m_data1;
 void print1() { cout << "private print1" << endl; }
protected:
 int m_data2;
 void print2() { cout << "protected print2" << endl; }
public:
 A(int x = 1, int y = 2, int z = 3) : m_data1(x), m_data2(y), m_data3(z) {}
 int m_data3;
 void print3() { cout << "protected print3" << endl; }
};

class B : private A
{
public:
 void test_public() {
  cout << m_data3 << endl;
  print3();
 }
 void test_protected() {
  cout << m_data2 << endl;
  print2();
 }
 void test_private() {
  // 下面两行编译不过，B类内无法访问父类的私有成员
  // cout << m_data1 << endl; 
  // print1();
 }
};


int main(int argc, char const* argv[])
{
 B b;
 b.test_public();
 b.test_protected();
 b.test_private();
 // cout << b.m_data3 << endl; // // 编译不过，子类对象无法访问父类public的成员
 // cout << b.m_data2 << endl; // 编译不过，子类对象无法访问父类protected的成员
 // cout << b.m_data1 << endl; // 编译不过，子类对象无法访问父类private的成员
 return 0;
}

#include<iostream>
#include<cstdio>

class Parent
{
public:
 Parent(int var=-1) {
  m_nPub = var;
  m_nPtd = var;
  m_bPrt = var;
 }
 int m_nPub;
protected:
 int m_nPtd;
private:
 int m_nPrt;
};

class Child1 : public Parent
{
public:
 int GetPub() { return m_nPub; }
 int GetPtd() { return m_nPtd; }
 int GetPrt() { return m_nPrt; }
 // A
};

class Child2 : protected Parent
{
public:
 int GetPub() { return m_nPub; }
 int GetPtd() { return m_nPtd; }
 int GetPrt() { return m_nPrt; }
 // B
};

class Child3 : private Parent
{
public:
 int GetPub() { return m_nPub; }
 int GetPtd() { return m_nPtd; }
 int GetPrt() { return m_nPrt; }
 // C
};

int main(int argc, char const *argv[])
{
 Child1 cd1;
 Child2 cd2;
 Child3 cd3;

 int nVar = 0;

 // public inherited
 cd1.m_nPub = nVar; // D
 cd1.m_nPtd = nVar; // E
 nVar = cd1.GetPtd(); // F

 // protected inherited
 cd2.m_nPub = nVar; // G
 nVar = cd2.GetPtd(); // H

 // private inherited
 cd3.m_nPub = nVar; // I
 nVar = cd3.GetPtd(); // J
 return 0;
}