C++ 继承及实现(一)

如果想透彻了解C++基础，可看微学院的C++入门教程

http://see.xidian.edu.cn/cpp/biancheng/view/91.html

C++继承可以是单一继承或多重继承，每一个继承连接可以是public,protected,private也可以是virtual或non-virtual。然后是各个成员函数选项可以是virtual或non-virtual或pure virtual。本文仅仅作出一些关键点的验证。

private（私有）和protected（保护）都能实现类的封装性。private能够对外部和子类保密，即除了成员所在的类本身可以访问之外，别的都不能直接访问。protected能够对外部保密，但允许子类直接访问这些成员。public、private和protected对成员数据或成员函数的保护程度可以用下表来描述：

　　public继承，例如下：

1 class base
2 ｛...｝
3 class derived:public base
4 ｛...｝

 1 #include 
  
   
 2 #include 
   
     3 4 class base 5 { 6 public: 7 base() 8 :baseName(""),baseData(0) 9 {} 10 11 base(std::string bn,int bd) 12 :baseName(bn),baseData(bd) 13 {} 14 15 std::string getBaseName() const 16 { 17 return baseName; 18 } 19 20 int getBaseData()const 21 { 22 return baseData; 23 } 24 25 private: 26 std::string baseName; 27 int baseData; 28 }; 29 30 class derived:public base 31 { 32 public: 33 derived():base(),derivedName("") 34 {} 35 derived(std::string bn,int bd,std::string dn) 36 :base(bn,bd),derivedName(dn) 37 {} 38 std::string getDerivedName() const 39 { 40 return derivedName; 41 } 42 private: 43 std::string derivedName; 44 }; 45 46 void show(std::string& info,const base& b) 47 { 48 info.append("Name is "); 49 info.append(b.getBaseName()); 50 info.append(", baseData is "); 51 char buffer[10]; 52 sprintf(buffer,"%d",b.getBaseData()); 53 info.append(buffer); 54 } 55 56 int main(int argc,char* argv[]) 57 { 58 base b("test",10); 59 std::string s; 60 show(s,b); 61 std::cout<
     
      
     
运行结果为：





 
     
base:baseName is test, baseData is 10
base:baseName is btest, baseData is 5
 
     
下面改改代码，将函数参数变为derived
 
      
     
void show2(std::string& info,const derived& d)
{
    info.append("Name is ");
    info.append(d.getBaseName());
    info.append(", baseData is ");
    char buffer[10];
    sprintf(buffer,"%d",d.getBaseData());
    info.append(buffer);
}
 
      
     
调用show(ss,d);编译器报错
 
     
1 derived_class.cpp: In function `int main(int, char**)':
2 derived_class.cpp:84: error: invalid initialization of reference of type 'const derived&' from expression of type 'base'
3 derived_class.cpp:70: error: in passing argument 2 of `void show2(std::string&, const derived&)'
 
     
第二点对各种形式的继承作出验证，首先给出表格
 
     
 
      
 
       
 
        
 继承方式\成员类型
 
        
 public
 
        
 protected
 
        
 private
 
       
 
       
 
        
 public
 
        
 public
 
        
 protected
 
        
 无法继承
 
       
 
       
 
        
 protected
 
        
 protected
 
        
 protected
 
        
 无法继承
 
       
 
       
 
        
 private
 
        
 private
 
        
 private
 
        
 无法继承
 
       
 
      
 
     
 
     
 这里解释一下，这里仅仅表达基类的成员，被public,protected,private三种方式继承后，在原基类为public,protectedc,private的成员在继承类里类型为表格里内容
 
      
     
 1 class base
 2 {
 3     public:
 4         std::string testPublic()
 5         {
 6             return std::string("this is public base");
 7         }
 8     protected:
 9         std::string testProtected()
10         {
11             return std::string("this is protected base");
12         }
13     private:
14         std::string testPrivate()
15         {
16             return std::string("this is private base");
17         }
18 };
19 
20 class derivedPublic:public base
21 {
22     public:
23         std::string testPubPublic()
24         {
25             return testPublic()+= "in derived";
26         }
27         
28         std::string testProPublic()
29         {    
30             return testProtected()+= "in derived";
31         }
32         
33         std::string testPriPublic()                   
34         {    
35             return testPrivate()+= "in derived";
36         }
37 };
38 
39 int main(int argc,char* argv[])
40 ｛
41     derivedPublic dpub;
42     std::cout << dpub.testPublic() << std::endl; 
43 ｝
 
      
     
 报下面错误，说明testPrivate()不是derived私有函数而是base的私有函数
 
     
derived11.cpp:16: e