C++(www.cppentry.com)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。
public继承，例如下：
1classbase2｛...｝3class derived:publicbase4 ｛...｝
如果这样写，编译器会理解成类型为derived的对象同时也是类型为base的对象，但类型为base的对象不是类型为derived的对象。这点很重要。那么函数形参为base类型适用于derived，形参为derived不适用于base。下面是验证代码，一个参数为base的函数，传入derived应该成功执行，相反，一个参数为derived的函数 1 #include <iostream> 2 #include <stdio.h> 3 4classbase 5{ 6public: 7base() 8 :baseName(""),baseData(0) 9 {}1011base(std::string bn,int bd)12 :baseName(bn),baseData(bd)13 {}1415 std::string getBaseName() const16 {17return baseName;18 }1920int getBaseData()const21 {22return baseData;23 }2425private:26 std::string baseName;27int baseData;28};2930class derived:publicbase31{32public: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() const39 {40return derivedName;41 }42private:43 std::string derivedName;44};4546void show(std::string& info,constbase& b)47{48 info.append("Name is ");49 info.append(b.getBaseName());50 info.append(", baseData is ");51char buffer[10];52 sprintf(buffer,"%d",b.getBaseData());53 info.append(buffer);54}5556int main(int argc,char* argv[])57{58base b("test",10);59 std::string s;60 show(s,b);61 std::cout<<s<<std::endl;62 derived d("btest",5,"dtest");63 std::string ss;64 show(ss,d);65 std::cout<<ss<<std::endl;66return0;67 }运行结果为：
base:baseName is test, baseData is10base:baseName is btest, baseData is5
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
1classbase 2{ 3public: 4 std::string testPublic() 5 { 6return std::string("this is public base"); 7 } 8protected: 9 std::string testProtected()10 {11return std::string("this is protected base");12 }13private:14 std::string testPrivate()15 {16return std::string("this is private base");17 }18};1920class derivedPublic:publicbase21{22public:23 std::string testPubPublic()24 {25return testPublic()+= "in derived";26 }2728 std::string testProPublic()29 { 30return testProtected()+= "in derived";31 }3233 std::string testPriPublic() 34 { 35return testPrivate()+= "in derived";36 }37};3839int 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: error: `std::stringbase::testPrivate()' is privatederived11.cpp:36: error: within this context
这样验证private类型成员无法被继承（public,private,protected）注：private，protected略去不做证明
下面只要验证 testProtected 能被第三层继承类继承，但是无法被第三层类直接调用就说明是public继承后继承类型为protected，而基类为Public类型成员则即可被继承又可以直接调用。
1 #include <iostream> 2 #include <string> 3 4classbase 5{ 6public: 7 std::string testPublic() 8 { 9return std::string("this is public base");10 }11protected:12 std::string testProtected()13 {14return std::string("this is protected base");15 }16private:17 std::string testPrivate()18 {19return std::string("this is private base");20 }21};2223class derivedPublic:publicbase24{25public:26 std::string testPubPublic()27 {28return testPublic()+= "in derived";29 }3031 std::string testProPublic()32 { 33return testProtected()+= "in derived";34 }3536// std::string testPriPublic() 37// { 38// return testPrivate()+= "in derived";39// }40};4142class deepDerived:public derivedPublic43{44public:45 std::string deepProtected()46 {47return testProtected() +="in deep";48 }4950 std::string deepPublic()51 {52return testPublic() +="indeep";53 }54};5556int main(int argc,char* argv[])57{58 derivedPublic dpub;59 std::cout << dpub.testProtected() << std::endl; 60 deepDerived deepdpub;61 std::cout<<deepdpub.testPublic() <<std::endl;62 std::cout<<deepdpub.testProtected() <<std::endl;63 std::cout<<deepdpub.deepProtected() <<std::endl;64 std::cout<<deepdpub.deepPublic() <<std::endl;65 }这里服务器报错
derived12.cpp:13: error: `std::stringbase::testProtected()' is protectedderived12.cpp:62: error: within this context
这样就验证了一个是public，一个是protected，protected是不能直接调用的，但是被继承后是可以被public成员调用的。
下面的已经证明，详细步骤就略去如果对该部分验证感兴趣，可以看下面代码。
View Code 1 #include <iostream> 2 #include <string> 3classbase 4{ 5public: 6 std::string testPublic() 7 { 8return std::string("this is public base"); 9 } 10protected: 11 std::string testProtected() 12 { 13return std::string("this is protected base"); 14 } 15private: 16 std::string testPrivate() 17 { 18return std::string("this is private base"); 19 } 20}; 21 22class derivedPublic:publicbase 23{ 24public: 25 std::string testPubPublic() 26 { 27return testPublic()+= "in derived"; 28 } 29 30 std::string testProPublic() 31 { 32return testProtected()+= "in derived"; 33 } 34 35// std::string testPriPublic() //私有成员并没有被继承下来 36// { 37// return testPrivate()+= "in derived"; 38// } 39}; 40 41class deepDerived:public derivedPublic 42{ 43public: 44 std::string test() 45 { 46return testPublic() +="in 3"; 47 } 48}; 49 50class derivedProtected:protectedbase 51{ 52public: 53 std::string testPubProtected() 54 { 55return testPublic()+= "in derived"; 56 } 57 58 std::string testProProtected() 59 { 60return testProtected()+= "in derived"; 61 } 62}; 63 64class deepDerived2:public derivedProtected 65{ 66public: 67 std::string test() 68 { 69return testPublic() +="in 3"; 70 } 71}; 72 73class derivedPrivate:privatebase 74{ 75public: 76 std::string testPubPirvate() 77 { 78return testPublic()+= "in derived"; 79 } 80 81 std::string testProPrivate() 82 { 83return testProtected()+= "in derived"; 84 } 85 86}; 87 88//class deepDerived3:public derivedPrivate 89//{ 90// public: 91// std::string test() 92// { 93// return testPublic() +="in 3"; 94// } 95//}; 96 97int main(int argc,char* argv[]) 98{ 99 derivedPublic dpub;100//derivedProtected dpro;101//derivedPrivate dpri;102 std::cout<<dpub.testPublic()<<std::endl; //103//std::cout<<dpub.testProtected()<<std::endl; //用户被继承也是无法使用104//cout<<dpub.testPrivate()<<std::endl; //基类都是私有函数105 std::cout<<dpub.testPubPublic()<<std::endl;106 std::cout<<dpub.testProPublic()<<std::endl;107//std::cout<<dpub.testPriPrivate()<<std::endl; //没有被继承108109 deepDerived dd;110 std::cout<<dd.test()<<std::endl;111112 derivedProtected dpro;113//std::cout<<dpro.testPublic()<<std::endl; //变成protected类型114 std::cout<<dpro.testPubProtected()<<std::endl;115 std::cout<<dpro.testProProtected()<<std::endl;116117 deepDerived2 dd2;118 std::cout<<dd2.test()<<std::endl;119120 derivedPrivate dpri;121 std::cout<<dpri.testPubPirvate()<<std::endl;122 std::cout<<dpri.testProPrivate()<<std::endl;123124// deepDerived3 dd3;125// std::cout<<dd3.test()<<std::endl;126 ｝