c++ protected,private.public

最新推荐文章于 2025-06-13 14:47:42 发布

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本文深入探讨了C++中public、protected和private访问修饰符的区别。Public成员对所有代码开放，Protected成员允许派生类访问，而Private成员仅限于类内部。选择Protected还是Private取决于对派生类程序员的信任程度。

转自：https://stackoverflow.com/questions/224966/private-and-protected-members-c

Public members of a class A are accessible for all and everyone.

Protected members of a class A are not accessible outside of A's code, but is accessible from the code of any class derived from A.

Private members of a class A are not accessible outside of A's code, or from the code of any class derived from A.

So, in the end, choosing between protected or private is answering the following questions: How much trust are you willing to put into the programmer of the derived class?

By default, assume the derived class is not to be trusted, and make your members private. If you have a very good reason to give free access of the mother class' internals to its derived classes, then you can make them protected.

Protected members can be accessed from derived classes. Private ones can't.

class Base {

private: 
  int MyPrivateInt;
protected: 
  int MyProtectedInt;
public:
  int MyPublicInt;
};

class Derived : Base
{
public:
  int foo1()  { return MyPrivateInt;} // Won't compile!
  int foo2()  { return MyProtectedInt;} // OK  
  int foo3()  { return MyPublicInt;} // OK
};‌‌

class Unrelated 
{
private:
  Base B;
public:
  int foo1()  { return B.MyPrivateInt;} // Won't compile!
  int foo2()  { return B.MyProtectedInt;} // Won't compile
  int foo3()  { return B.MyPublicInt;} // OK
};