C++繼承介紹
然后是各個(gè)成員函數(shù)選項(xiàng)可以是virtual或non-virtual或pure virtual。本文僅僅作出一些關(guān)鍵點(diǎn)的驗(yàn)證。
public繼承，例如下：
class base
｛...｝
class derived:public base
｛...｝
如果這樣寫，編譯器會(huì)理解成類型為derived的對(duì)象同時(shí)也是類型為base的對(duì)象，但類型為base的對(duì)象不是類型為derived的對(duì)象。這點(diǎn)很重要。那么函數(shù)形參為base類型適用于derived，形參為derived不適用于base。下面是驗(yàn)證代碼，一個(gè)參數(shù)為base的函數(shù)，傳入derived應(yīng)該成功執(zhí)行，相反，一個(gè)參數(shù)為derived的函數(shù)
#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;
}
運(yùn)行結(jié)果為：
base:baseName is test, baseData is 10
base:baseName is btest, baseData is 5
下面改改代碼，將函數(shù)參數(shù)變?yōu)閐erived
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);
}
調(diào)用show(ss,d);編譯器報(bào)錯(cuò)
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&)'第二點(diǎn)對(duì)各種形式的繼承作出驗(yàn)證，首先給出表格
| 繼承方式\成員類型 | public | protected | private |
| public | public | protected | 無法繼承 |
| protected | protected | protected | 無法繼承 |
| private | private | private | 無法繼承 |
這里解釋一下，這里僅僅表達(dá)基類的成員，被public,protected,private三種方式繼承后，在原基類為public,protectedc,private的成員在繼承類里類型為表格里內(nèi)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;
｝
報(bào)下面錯(cuò)誤，說明testPrivate()不是derived私有函數(shù)而是base的私有函數(shù)
derived11.cpp:16: error: `std::string base::testPrivate()' is private
derived11.cpp:36: error: within this context這樣驗(yàn)證private類型成員無法被繼承（public,private,protected）注：private，protected略去不做證明
下面只要驗(yàn)證 testProtected 能被第三層繼承類繼承，但是無法被第三層類直接調(diào)用就說明是public繼承后繼承類型為protected，而基類為Public類型成員則即可被繼承又可以直接調(diào)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;
}
這里服務(wù)器報(bào)錯(cuò)
derived12.cpp:13: error: `std::string base::testProtected()' is protected
derived12.cpp:62: error: within this context這樣就驗(yàn)證了一個(gè)是public，一個(gè)是protected，protected是不能直接調(diào)用的，但是被繼承后是可以被public成員調(diào)用的。
下面的已經(jīng)證明，詳細(xì)步驟就略去如果對(duì)該部分驗(yàn)證感興趣，可以看下面代碼。
#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() //私有成員并沒有被繼承下來
// {
// 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; //用戶被繼承也是無法使用
//cout<<dpub.testPrivate()<<std::endl; //基類都是私有函數(shù)
std::cout<<dpub.testPubPublic()<<std::endl;
std::cout<<dpub.testProPublic()<<std::endl;
//std::cout<<dpub.testPriPrivate()<<std::endl; //沒有被繼承
deepDerived dd;
std::cout<<dd.test()<<std::endl;
derivedProtected dpro;
//std::cout<<dpro.testPublic()<<std::endl; //變成protected類型
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;
｝
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