c++访问私有成员变量和私有成员函数的常用方法

朱雀 2022-12-04 01:21 904阅读 0赞

类的对象不能直接访问类声明的私有成员变量，否则破坏了信息隐藏的目的。  
在C++中，为了防止某些数据成员或成员函数从外部被直接访问，可以将它们声明为private，这样编译器会阻止任何来自外部非友元的直接访问。

**1.私有成员变量的四种访问方法**

(1)通过公共函数为私有成员赋值

#include <iostream>  
    using namespace std;  
     
    class Test  
    {  
    private:  
    	int x, y;  
    public:  
    	void setX(int a)  
    	{  
    		x=a;  
    	}  
    	void setY(int b)  
    	{  
    		y=b;  
    	}  
    	void print(void)  
    	{  
    		cout<<"x="<<x<<'\t'<<"y="<<y<<endl;  
    	}  
    } ; 
     
    int main()  
    {  
    	Test p1;  
    	p1.setX(1);  
    	p1.setY(9);  
    	p1.print( );  
    	return 0;  
    }

(2)利用函数访问私有数据成员

#include <iostream>  
    using namespace std;  
    class Test  
    {  
    private:  
    	int x,y;  
    public:  
    	void setX(int a)  
    	{  
    		x=a;  
    	}  
    	void setY(int b)  
    	{  
    		y=b;  
    	}  
    	int getX(void)  
    	{  
    		return x;   //返回x值  
    	}  
    	int getY(void)  
    	{  
    		return y;   //返回y值  
    	}  
    };  
    int main()  
    {  
    	Test p1;  
    	p1.setX(1);  
    	p1.setY(9);  
    	int a,b;  
    	a=p1.getX( );  
    	b=p1.getY();  
    	cout<<a<<'\t'<<b<<endl;  
    	return 0;  
    }

(3)利用引用访问私有数据成员

#include <iostream>  
    using namespace std;  
    class Test  
    {  
    private:  
    	int x,y;  
    public:  
    	void setX(int a)  
    	{  
    		x=a;  
    	}  
    	void setY(int b)  
    	{  
    		y=b;  
    	}  
    	void getXY(int &px, int &py) //引用  
    	{  
    		px=x;    //提取x,y值  
    		py=y;  
    	}  
    };  
    int main()  
    {  
    	Test p1,p2;  
    	p1.setX(1);  
    	p1.setY(9);  
    	int a,b;  
    	p1.getXY(a, b); //将 a=x, b=y  
    	cout<<a<<'\t'<<b<<endl;  
    	return 0;  
    }

(4)利用指针访问私有数据成员

#include <iostream>  
    using namespace std;  
    class Test  
    {  
    private:  
    	int x,y;  
    public:  
    	void setX(int a)  
    	{  
    		x=a;  
    	}  
    	void setY(int b)  
    	{  
    		y=b;  
    	}  
    	void getXY(int *px, int *py)  
    	{  
    		*px=x;    //提取x,y值  
    		*py=y;  
    	}  
    };  
    int main()  
    {  
    	Test p1;  
    	p1.setX(1);  
    	p1.setY(9);  
    	int a,b;  
    	p1.getXY(&a,&b);  //将 a=x, b=y  
    	cout<<a<<'\t'<<b<<endl;  
    	return 0;  
    }

详见 [https://blog.csdn.net/KgdYsg/article/details/82492797?ops\_request\_misc=%257B%2522request%255Fid%2522%253A%2522159922886019724839809393%2522%252C%2522scm%2522%253A%252220140713.130102334.pc%255Fall.%2522%257D&request\_id=159922886019724839809393&biz\_id=0&utm\_medium=distribute.pc\_search\_result.none-task-blog-2~all~first\_rank\_ecpm\_v3~pc\_rank\_v3-2-82492797.pc\_ecpm\_v3\_pc\_rank\_v3&utm\_term=c%2B%2B%E8%AE%BF%E9%97%AE%E7%A7%81%E6%9C%89private%E6%88%90%E5%91%98%E5%8F%98%E9%87%8F%E7%9A%84%E5%B8%B8%E7%94%A8%E6%96%B9%E6%B3%95&spm=1018.2118.3001.4187][https_blog.csdn.net_KgdYsg_article_details_82492797_ops_request_misc_257B_2522request_255Fid_2522_253A_2522159922886019724839809393_2522_252C_2522scm_2522_253A_252220140713.130102334.pc_255Fall._2522_257D_request_id_159922886019724839809393_biz_id_0_utm_medium_distribute.pc_search_result.none-task-blog-2_all_first_rank_ecpm_v3_pc_rank_v3-2-82492797.pc_ecpm_v3_pc_rank_v3_utm_term_c_2B_2B_E8_AE_BF_E9_97_AE_E7_A7_81_E6_9C_89private_E6_88_90_E5_91_98_E5_8F_98_E9_87_8F_E7_9A_84_E5_B8_B8_E7_94_A8_E6_96_B9_E6_B3_95_spm_1018.2118.3001.4187]

**2.在类外调用类的私有成员函数的两种方法**

（1）.通过类的public成员函数调用private成员函数

#include<iostream>
    using namespace std;
    class Test
    {
        public:
            void fun2()
            {
                fun1();
            }
        private:
            void fun1()
            {
                cout<<"fun1"<<endl;
            }
    };
    int main()
    {
        Test t;
        t.fun2();
        return 0;
    }

（2）.通过类的友元函数调用该类的private成员函数，但是该成员函数必须设为static,这样就可以在友元函数内通过类名调用，否则无法调用

#include<iostream>
    using namespace std;
    class Test
    {
        friend void fun2(); //fun2()设为类Test的友元函数
     private:
         static void fun1()
         {
             cout<<"fun1"<<endl;
         }
    };
    void fun2()
    {
        Test::fun1();
    }
    int main()
    {
        fun2();
        return 0;
    }

详见 [https://blog.csdn.net/jackchoise030/article/details/86158780][https_blog.csdn.net_jackchoise030_article_details_86158780]

[https_blog.csdn.net_KgdYsg_article_details_82492797_ops_request_misc_257B_2522request_255Fid_2522_253A_2522159922886019724839809393_2522_252C_2522scm_2522_253A_252220140713.130102334.pc_255Fall._2522_257D_request_id_159922886019724839809393_biz_id_0_utm_medium_distribute.pc_search_result.none-task-blog-2_all_first_rank_ecpm_v3_pc_rank_v3-2-82492797.pc_ecpm_v3_pc_rank_v3_utm_term_c_2B_2B_E8_AE_BF_E9_97_AE_E7_A7_81_E6_9C_89private_E6_88_90_E5_91_98_E5_8F_98_E9_87_8F_E7_9A_84_E5_B8_B8_E7_94_A8_E6_96_B9_E6_B3_95_spm_1018.2118.3001.4187]: https://blog.csdn.net/KgdYsg/article/details/82492797?ops_request_misc=%257B%2522request%255Fid%2522%253A%2522159922886019724839809393%2522%252C%2522scm%2522%253A%252220140713.130102334.pc%255Fall.%2522%257D&request_id=159922886019724839809393&biz_id=0&utm_medium=distribute.pc_search_result.none-task-blog-2~all~first_rank_ecpm_v3~pc_rank_v3-2-82492797.pc_ecpm_v3_pc_rank_v3&utm_term=c%2B%2B%E8%AE%BF%E9%97%AE%E7%A7%81%E6%9C%89private%E6%88%90%E5%91%98%E5%8F%98%E9%87%8F%E7%9A%84%E5%B8%B8%E7%94%A8%E6%96%B9%E6%B3%95&spm=1018.2118.3001.4187
[https_blog.csdn.net_jackchoise030_article_details_86158780]: https://blog.csdn.net/jackchoise030/article/details/86158780