C++ 继承详解及实例代码

2020-05-23 14:00:20

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　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。

　　public继承，例如下：

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

　　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

#include <iostream>#include <stdio.h>class base{  public:  base()  :baseName(""),baseData(0)  {}    base(std::string bn,int bd)  :baseName(bn),baseData(bd)  {}    std::string getBaseName() const  {    return baseName;  }    int getBaseData()const  {    return baseData;  }    private:    std::string baseName;    int baseData;};class derived:public base{  public:    derived():base(),derivedName("")    {}    derived(std::string bn,int bd,std::string dn)    :base(bn,bd),derivedName(dn)    {}    std::string getDerivedName() const    {      return derivedName;    }  private:    std::string derivedName;};void show(std::string& info,const base& b){  info.append("Name is ");  info.append(b.getBaseName());  info.append(", baseData is ");  char buffer[10];  sprintf(buffer,"%d",b.getBaseData());    info.append(buffer);}int main(int argc,char* argv[]){  base b("test",10);  std::string s;  show(s,b);  std::cout<<s<<std::endl;  derived d("btest",5,"dtest");  std::string ss;  show(ss,d);  std::cout<<ss<<std::endl;  return 0;}

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

class base{  public:    std::string testPublic()    {      return std::string("this is public base");    }  protected:    std::string testProtected()    {      return std::string("this is protected base");    }  private:    std::string testPrivate()    {      return std::string("this is private base");    }};class derivedPublic:public base{  public:    std::string testPubPublic()    {      return testPublic()+= "in derived";    }        std::string testProPublic()    {        return testProtected()+= "in derived";    }        std::string testPriPublic()              {        return testPrivate()+= "in derived";    }};int main(int argc,char* argv[])｛  derivedPublic dpub;  std::cout << dpub.testPublic() << std::endl; ｝

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::string base::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。

#include <iostream>#include <string>class base{  public:    std::string testPublic()    {      return std::string("this is public base");    }  protected:    std::string testProtected()    {      return std::string("this is protected base");    }  private:    std::string testPrivate()    {      return std::string("this is private base");    }};class derivedPublic:public base{  public:    std::string testPubPublic()    {      return testPublic()+= "in derived";    }        std::string testProPublic()    {        return testProtected()+= "in derived";    }    //    std::string testPriPublic()          //    {  //      return testPrivate()+= "in derived";//    }};class deepDerived:public derivedPublic{  public:    std::string deepProtected()    {      return testProtected() +="in deep";    }        std::string deepPublic()    {      return testPublic() +="indeep";    }};int main(int argc,char* argv[]){  derivedPublic dpub;  std::cout << dpub.testProtected() << std::endl;   deepDerived deepdpub;  std::cout<<deepdpub.testPublic() <<std::endl;  std::cout<<deepdpub.testProtected() <<std::endl;  std::cout<<deepdpub.deepProtected() <<std::endl;  std::cout<<deepdpub.deepPublic() <<std::endl;}

这里服务器报错

derived12.cpp:13: error: `std::string base::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。

#include <iostream>#include <string>class base{  public:    std::string testPublic()    {      return std::string("this is public base");    }  protected:    std::string testProtected()    {      return std::string("this is protected base");    }  private:    std::string testPrivate()    {      return std::string("this is private base");    }};class derivedPublic:public base{  public:    std::string testPubPublic()    {      return testPublic()+= "in derived";    }        std::string testProPublic()    {        return testProtected()+= "in derived";    }    //    std::string testPriPublic()          //私有成员并没有被继承下来//    {  //      return testPrivate()+= "in derived";//    }};class deepDerived:public derivedPublic{  public:    std::string test()    {      return testPublic() +="in 3";    }};class derivedProtected:protected base{  public:    std::string testPubProtected()    {      return testPublic()+= "in derived";    }        std::string testProProtected()    {        return testProtected()+= "in derived";    }};class deepDerived2:public derivedProtected{  public:    std::string test()    {      return testPublic() +="in 3";    }};class derivedPrivate:private base{  public:    std::string testPubPirvate()    {      return testPublic()+= "in derived";    }        std::string testProPrivate()    {        return testProtected()+= "in derived";    }    };//class deepDerived3:public derivedPrivate//{//  public://    std::string test()//    {//      return testPublic() +="in 3";//    }//};int main(int argc,char* argv[]){  derivedPublic dpub;  //derivedProtected dpro;  //derivedPrivate dpri;  std::cout<<dpub.testPublic()<<std::endl;    //  //std::cout<<dpub.testProtected()<<std::endl;  //用户被继承也是无法使用  //cout<<dpub.testPrivate()<<std::endl;     //基类都是私有函数  std::cout<<dpub.testPubPublic()<<std::endl;  std::cout<<dpub.testProPublic()<<std::endl;  //std::cout<<dpub.testPriPrivate()<<std::endl; //没有被继承    deepDerived dd;  std::cout<<dd.test()<<std::endl;      derivedProtected dpro;  //std::cout<<dpro.testPublic()<<std::endl;    //变成protected类型  std::cout<<dpro.testPubProtected()<<std::endl;  std::cout<<dpro.testProProtected()<<std::endl;      deepDerived2 dd2;  std::cout<<dd2.test()<<std::endl;      derivedPrivate dpri;  std::cout<<dpri.testPubPirvate()<<std::endl;  std::cout<<dpri.testProPrivate()<<std::endl;  //  deepDerived3 dd3;//  std::cout<<dd3.test()<<std::endl;｝

以上就是对C++ j继承的资料整理，后续继续补充相关资料，谢谢大家对本站的支持！

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