示例中C++中Private和Protected之间的区别

受保护的

受保护的访问修饰符与私有访问修饰符相似，不同之处在于，声明为“受保护”的类成员在该类外部无法访问，但可以由该类的任何子类(派生类)访问。

例子：

// C++ program to demonstrate
// protected access modifier
  
#include 
using namespace std;
  
// base class
class Parent {
  
    // protected data members
protected:
    int id_protected;
};
  
// sub class or derived class
class Child : public Parent {
  
public:
    void setId(int id)
    {
  
        // Child class is able to access the inherited
        // protected data members of the base class
  
        id_protected = id;
    }
  
    void displayId()
    {
        cout << "id_protected is: "
             << id_protected << endl;
    }
};
  
// main function
int main()
{
  
    Child obj1;
  
    // member function of the derived class can
    // access the protected data members of the base class
  
    obj1.setId(81);
    obj1.displayId();
    return 0;
}

输出：

id_protected is: 81

私人的

声明为私有的类成员只能由该类内部的函数访问。类之外的任何对象或函数都不允许直接访问它们。只允许成员函数或朋友函数访问类的私有数据成员。

例子：

// C++ program to demonstrate private
// access modifier
  
#include 
using namespace std;
  
class Circle {
  
    // private data member
private:
    double radius;
  
    // public member function
public:
    void compute_area(double r)
    {
        // member function can access private
        // data member radius
        radius = r;
  
        double area = 3.14 * radius * radius;
  
        cout << "Radius is: " << radius << endl;
        cout << "Area is: " << area;
    }
};
  
// main function
int main()
{
    // creating object of the class
    Circle obj;
  
    // trying to access private data member
    // directly outside the class
    obj.compute_area(1.5);
  
    return 0;
}

输出：

Radius is: 1.5
Area is: 7.065

私有与受保护之间的区别

Private	Protected
The class members declared as private can be accessed only by the functions inside the class.	Protected access modifier is similar to that of private access modifiers.
Only the member functions or the friend functions are allowed to access the private data members of a class.	The class member declared as Protected are inaccessible outside the class but they can be accessed by any subclass(derived class) of that class.

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