C++ 繼承詳解及實(shí)例代碼

來(lái)源：本站原創(chuàng)|時(shí)間：2020-01-10|欄目：C語(yǔ)言|點(diǎn)擊：次

　C++繼承可以是單一繼承或多重繼承，每一個(gè)繼承連接可以是public,protected,private也可以是virtual或non-virtual。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：

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

　　如果這樣寫(xiě)，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)

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(wú)法繼承
protected	protected	protected	無(wú)法繼承
private	private	private	無(wú)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(shuō)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(wú)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(wú)法被第三層類直接調(diào)用就說(shuō)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>
#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()          //私有成員并沒(méi)有被繼承下來(lái)
//    {  
//      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(wú)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(méi)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;
｝

以上就是對(duì)C++ j繼承的資料整理，后續(xù)繼續(xù)補(bǔ)充相關(guān)資料，謝謝大家對(duì)本站的支持！

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