C++之模板类指向子类对象(一百四十六)-Toy模板网

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C++之模板类指向子类对象(一百四十六),C++入门系列,c++,开发语言

1.前言

本篇目的：理解模板类指向子类对象应用。文章来源地址https://www.toymoban.com/news/detail-516998.html

2.应用实例

<1>.v1.0 基础版

#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 升级版

#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);
}

<3>.v3.0 仿Refbase例子

#include <iostream>
#include <string>

using namespace std;

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

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

template <typename INTERFACE>
class BpInterface : public INTERFACE, BpRefBase{
public:
  BpInterface(INTERFACE* ptr) : mPtr(ptr) {}
  void print(string cmd) {
    printf("xxx---------->%s(), line = %d, type(class) = %s\n",__FUNCTION__,__LINE__,typeid(INTERFACE).name());
  }
  INTERFACE *get(){
    return mPtr;
  }

  void takePicture() override {
    printf("xxx---------->%s(), line = %d\n",__FUNCTION__,__LINE__);
  }

  INTERFACE* mPtr;
};


class ICameraService {
public:
  virtual void takePicture() = 0;
};

class CameraService : public ICameraService {
public:

  void takePicture() override {
    printf("xxx---------->%s(), line = %d\n",__FUNCTION__,__LINE__);
  }
};

int main() {
#if 0
  //第一种方式
/*
  CameraService 类是 ICameraService 接口的子类，而 BpInterface 类是一个模板类，它的模板参数是 ICameraService。在这个语句中，我们创建了一个 CameraService 类的对象，并将其赋值给了 BpInterface<ICameraService> 类型的变量 bpInterface。

  由于 CameraService 是 ICameraService 的子类，所以它满足了 BpInterface 类对模板参数的要求。因此，我们可以将 CameraService 对象赋值给 BpInterface<ICameraService> 类型的变量。

  这种用子类对象赋值给父类指针或引用的行为被称为多态。在多态中，我们可以使用父类的指针或引用来操作子类的对象，这样可以实现代码的灵活性和可扩展性。
  */
  //1.父类ICameraService指向子类对象CameraService
  BpInterface<ICameraService> bpInterface = new CameraService();

  //2.调用BpInterface类的成员函数print()
  bpInterface.print("123");

  //3.通过BpInterface类的mPtr指针,调用CameraService类重写的纯虚函数takePicture().
  bpInterface.get()->takePicture();
#else
  //第二种方式
  ICameraService *cameraService = new CameraService();
  BpInterface<ICameraService> *bpInterface = new BpInterface<ICameraService>(cameraService);
  bpInterface->print("123");
  bpInterface->get()->takePicture();
#endif

  return 0;
}

<4>.v4.0 父类指针指向子类对象区别

(1).

#include<iostream>
#include <typeinfo>
using namespace std;

template<typename SERVICE>
class BaseA{
public:
  BaseA(){
    mptr = new SERVICE;
  }
  void test(){
    printf("xxx--------->%s(), line = %d\n",__FUNCTION__,__LINE__);
  }

    SERVICE *get(){
    return mptr;
  }
  SERVICE *mptr;
};

class Parent{
public:
  static const char *getName() { return "media.audio"; }
};

class Derived: public BaseA<Parent>{
  friend class BaseA<Parent>;
public:
  Derived(){}
};

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

  //2.调用类模板BaseA的成成员函数test.
  b->test();

  //3.调用传入模板类的Parent的成员函数getName.
  const char *name = b->get()->getName();
  printf("xxx--------->%s(), line = %d,name = %s\n",__FUNCTION__,__LINE__,name);

}

(2)

#include<iostream>
#include <typeinfo>
using namespace std;

#define NTD

template<typename SERVICE>
class BaseA{
public:
  BaseA(SERVICE *ptr) : mPtr(ptr){
    printf("xxx--------->line = %d, type = %s, name = %s\n",__LINE__,typeid(SERVICE).name(),SERVICE::getName());
  }
  SERVICE *get(){
    printf("xxx--------->%s(), line = %d\n",__FUNCTION__,__LINE__);
    return mPtr;
  }
  void test(){
    printf("xxx--------->%s(), line = %d\n",__FUNCTION__,__LINE__);
  }
  SERVICE *mPtr;
};

class Parent{
public:
  static const char *getName() { return "media.audio"; }
  int value = 100;
};

class Derived: public Parent{
public:
  int count = 200;
};

int main(){
    //第一种方式:
  //1.父类BaseA<Parent>模板类指向子类对象Derived
  BaseA<Parent> b = new Derived();
/*
  将Parent类传入类模板BaseA,接着进入BaseA模板类构造函数初始化列表,进行初始化,将类Parent指针对象ptr传递给传给模板类的BaseA的成员变量mPtr,模板类b，因为Device继承自Parent类，将Device对象赋值给b。
  子类对象赋值给父类指针或引用的行为被称为多态。在多态中，我们可以使用父类的指针或引用来操作子类的对象
*/
  //2.调用类模板BaseA的成成员函数test.
  b.test();

  //3.调用传入模板类的Parent的成员函数getName.
  const char *name = b.mPtr->getName();
  printf("xxx--------->%s(), line = %d,name = %s\n",__FUNCTION__,__LINE__,name);

  //4.
  int val = b.get()->value;
  printf("xxx--------->%s(), line = %d,val = %d\n",__FUNCTION__,__LINE__,val);


  //第二种方式:
  BaseA<Parent> *bb = new BaseA<Parent>(new Derived());
  bb->test();
  const char *name_01 = bb->mPtr->getName();
}

<5>.v5.0 仿CameraService::instantiate()例子

#include <iostream>
using namespace std;

template<typename SERVICE>
class BinderService{
public:
  static void instantiate() {
    printf("xxx-------->line = %d, service_name = '%s'\n",__LINE__,SERVICE::getServiceName());

    SERVICE *cm = new SERVICE();
    printf("xxx-------->line = %d, count = %d, type(name) = %s\n",__LINE__,cm->count,typeid(SERVICE).name());
  }
};

class CameraService : public BinderService<CameraService>{
  friend class BinderService<CameraService>;

  static char const* getServiceName() { return "media.camera"; }
  int count = 220;
};

int main(){
  //way01:
  CameraService::instantiate();

  //way02:
  CameraService *cm = new CameraService;
  cm->instantiate();
}