c++中类中私有成员的调用？

Question

#include <iostream>
using namespace std;
class test{
      private:
            int a;
            int b;
      public:
            test(int a = 1, int b = 2){
                  this->a = a;
                  this->b = b;
            }
            int re(test ccc){
                  a = ccc.a + 444;
                  b = ccc.b + 444;
            }
};

为什么re函数中的ccc可以直接调用a和b而不报错？

Answer 1

搜了下（关键字： c++ access class private variable），这里有不错的解释：

http://stackoverflow.com/questions/7396846/with-a-private-modifier-why-can-the-member-in-other-objects-be-accessed-directl

Good question. The point is that protection in C++ is class level, not object level. So a method being invoked on one object can access private members of any other instance of the same class.

This makes sense if you see the role of protection being to allow encapsulation to ensure that the writer of a class can build a cohesive class, and not have to protect against external code modifying object contents.

Another thought as to the real "why?". Consider how you write almost any copy constructor; you want access to the original's underlying data structure, not its presented interface.

Answer 2

Because a class in C++ is a friend class of its own class.

Answer 3

Because a and b are both members of the test class.

Answer 4

Methods of a class can access its own private members

Answer 5

Different objects of the same class can access each other’s private members

Answer 6

Of course it can be in a class

Answer 7

Private data cannot be accessed directly and can only be called through member functions and friend functions of the class.

Answer 8

Friend functions http://learn.jser.com/cplusplus/cpp-friend-functions.html