C++继承介绍，继承的方式有哪些？

各个成员函数选项可以是virtual或non-virtual或pure virtual。

public继承，例如下：

class base
｛...｝
class derived:public base
｛...｝

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

derived_class.cpp: In function `int main(int, char**)':
derived_class.cpp:84: error: invalid initialization of reference of type 'const derived&' from expression of type 'base'
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

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 private

derived11.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 protected

derived12.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>
2 #include <string>
3 class base
4 {
5     public:
6         std::string testPublic()
7         {
8             return std::string("this is public base");
9         }
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;
｝