C++编程中私有和保护以及公有的类成员访问控制

private:
  [member-list]
private base-class

// keyword_private.cpp
class BaseClass {
public:
  // privMem accessible from member function
  int pubFunc() { return privMem; }
private:
  void privMem;
};

class DerivedClass : public BaseClass {
public:
  void usePrivate( int i )
   { privMem = i; }  // C2248: privMem not accessible
             // from derived class
};

class DerivedClass2 : private BaseClass {
public:
  // pubFunc() accessible from derived class
  int usePublic() { return pubFunc(); }
};

int main() {
  BaseClass aBase;
  DerivedClass aDerived;
  DerivedClass2 aDerived2;
  aBase.privMem = 1;   // C2248: privMem not accessible
  aDerived.privMem = 1; // C2248: privMem not accessible
             //  in derived class
  aDerived2.pubFunc();  // C2247: pubFunc() is private in
             //  derived class
}

protected:
  [member-list]
protected base-class

// keyword_protected.cpp
// compile with: /EHsc
#include <iostream>

using namespace std;
class X {
public:
  void setProtMemb( int i ) { m_protMemb = i; }
  void Display() { cout << m_protMemb << endl; }
protected:
  int m_protMemb;
  void Protfunc() { cout << "\nAccess allowed\n"; }
} x;

class Y : public X {
public:
  void useProtfunc() { Protfunc(); }
} y;

int main() {
  // x.m_protMemb;     error, m_protMemb is protected
  x.setProtMemb( 0 );  // OK, uses public access function
  x.Display();
  y.setProtMemb( 5 );  // OK, uses public access function
  y.Display();
  // x.Protfunc();     error, Protfunc() is protected
  y.useProtfunc();   // OK, uses public access function
            // in derived class
}

public:
  [member-list]
public base-class

// keyword_public.cpp
class BaseClass {
public:
  int pubFunc() { return 0; }
};

class DerivedClass : public BaseClass {};

int main() {
  BaseClass aBase;
  DerivedClass aDerived;
  aBase.pubFunc();    // pubFunc() is accessible 
             //  from any function
  aDerived.pubFunc();  // pubFunc() is still public in 
             //  derived class
}