c++中类中私有成员的调用？

问题描述

问 题

#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？

解决方案

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.

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