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1.前言

本篇目的：理解模板类指向子类对象应用。

2.应用实例

<1>.v1.0

#include<iostream>
using namespace std;

template<typename SERVICE>
class BaseA{
public:

  BaseA(){
    //printf("xxx--------->%s(), line = %d, i = %s\n",__FUNCTION__,__LINE__,SERVICE::getServiceName());
  }
  virtual void test(int i) = 0;//纯虚函数，子类必须实现.
};

class Parent{
public:
  Parent(){
    printf("xxx--------->%s(), line = %d\n",__FUNCTION__,__LINE__);
  }
};


//Derived继承自类模板BaseA<任意类型>.将子类的类型传参给模板类,在模板类可以调用子类Derived的getServiceName()和value
class Derived: public BaseA<Derived>{
  friend class BaseA<Derived>;
public:
  void test(int i){
    printf("xxx--------->%s(), line = %d, i = %d\n",__FUNCTION__,__LINE__,i);
  }
  static const char *getServiceName() { return "media.audio_policy"; }
  int value = 100;
};

int main(){
  //1.子类指向子类对象
  Derived *dr = new Derived();
  dr->test(777);
  printf("xxx--------->%s(), line = %d, value = %d\n",__FUNCTION__,__LINE__,dr->value);

  //2.父类指向子类对象
  BaseA<Derived> *b = new Derived;
  b->test(999);
  //printf("xxx--------->%s(), line = %d, value = %d\n",__FUNCTION__,__LINE__,b->value);//error
}

<2>.v2.0

#include<iostream>
using namespace std;

template<typename SERVICE>
class BaseA{
public:

  BaseA(){
    printf("xxx--------->%s(), line = %d, i = %s\n",__FUNCTION__,__LINE__,SERVICE::getName());
  }
  virtual void test(int i) = 0;//纯虚函数，子类必须实现.
};

class Parent{
public:
  Parent(){
    printf("xxx--------->%s(), line = %d\n",__FUNCTION__,__LINE__);
  }
  static const char *getName() { return "Hello Test."; }
};

class Derived: public BaseA<Parent>{
  friend class BaseA<Parent>;
public:
  void test(int i){
    printf("xxx--------->%s(), line = %d, i = %d\n",__FUNCTION__,__LINE__,i);
  }
  static const char *getServiceName() { return "media.audio_policy"; }
  int value = 100;
};

int main(){
  //1.父类BaseA<Parent>模板类指向子类对象Derived
  BaseA<Parent> *b = new Derived();
  b->test(999);
}