C++动态创建对象

1.类似java中的反射

2.动态获取类型信息（方法与属性）

3.动态创建对象

  动态调用对象的方法

  动态操作对象的属性

  需要给每个类添加原数据

   对原有的类不做任何改，只需要增加一个宏就能够动态创建

4.动态创建对象
  1)避免if,else编写，增加扩展性
  2)将类名放到配置文件中，组件初步
  组件A，主程序组件A；
  后来出现组件B，主程序下载组件B，更新配置文件；主程序读取配置文件，获得方法

5.代码如下：添加REGISTER_CLASS(类名)，即可动态创建

   sh make.sh生成可执行文件

   ./test

DynBase.h#ifndef _DYNBASE_H_#define _DYNBASE_H_#include <map>#include <string>using namespace std;typedef void* (*CREATE_FUNC)();class DynObjectFactory {public:static void* CreateObject(const string& name) {map<string, CREATE_FUNC>::const_iterator it;it = mapCls_.find(name);if(it == mapCls_.end()) {return NULL;} else {//return it->second();return (*it->second)();}}static void  Register(const string& name, CREATE_FUNC func) {mapCls_[name] = func;}private:static map<string, CREATE_FUNC> mapCls_;};//__declspec(selectany) map<string, CREATE_FUNC> DynObjectFactory::mapCls_;//map<string, CREATE_FUNC> DynObjectFactory::mapCls_;  // DynTest.cpp中使用DynBase.h;Shape.cpp中使用DynBase.h__attribute((weak))map<string, CREATE_FUNC> DynObjectFactory::mapCls_;class Register {public:Register(const string& name, CREATE_FUNC func) {DynObjectFactory::Register(name, func);}};#define REGISTER_CLASS(class_name)\class class_name##Register {\public:\static void* NewInstance() {\return new class_name;\}\private:\static Register reg_;\};\Register class_name##Register::reg_(#class_name, class_name##Register::NewInstance);#endif // _DYNBASE_H_

REGISTER_CLASS也可以使用模板

template<typename T>class DelegatingClass {public:DelegatingClass(const string& name) {DynObjectFactory::Register(name, &(DelegatingClass::NewInstance));}static void* NewInstance() {return new T;}};#define REGISTER_CLASS(class_name) DelegatingClass<class_name> class##class_name(#class_name)

Shape.h#ifndef _SHAPE_H_#define _SHAPE_H_class Shape {public:virtual void Draw() = 0;virtual ~Shape() {};};class Circle: public Shape {public:virtual void Draw() override;virtual ~Circle() override;};class Square: public Shape {public:virtual void Draw() override;virtual ~Square() override;};class Rectangle: public Shape {public:virtual void Draw() override;virtual ~Rectangle() override;};#endif // _SHAPE_H_

Shape.cpp#include "Shape.h"#include "DynBase.h"#include <iostream>using namespace std;void Circle::Draw() {cout << "Circle::Draw()" << endl;}Circle::~Circle() {cout << "~Circle ..." << endl;}void Square::Draw() {cout << "Square::Draw()" << endl;}Square::~Square() {cout << "~Square ..." << endl;}void Rectangle::Draw() {cout << "Rectangle::Draw()" << endl;}Rectangle::~Rectangle() {cout << "~Rectangle ..." << endl;}REGISTER_CLASS(Circle);REGISTER_CLASS(Square);REGISTER_CLASS(Rectangle);/*class CircleRegister {public:static void* NewInstance() {return new Ciecle;}private:static Register reg_;  //声明};Register CircleRegister::reg_("Circle", CircleRegister::NewInstance);DynObjectFactory::Register("Circle", CircleRegister::NewInstance);mapCls_["Circle"] = CircleRegister::NewInstance; */

DynTest.cpp#include <iostream>#include "Shape.h"#include "DynBase.h"#include <vector>#include <string>using namespace std;void DrawAllShapes(const vector<Shape*>& v) {vector<Shape*>::const_iterator it;for(it = v.begin(); it != v.end(); ++it) {(*it)->Draw();}}void DeleteAllShapes(const vector<Shape*>& v) {vector<Shape*>::const_iterator it;for(it = v.begin(); it != v.end(); ++it) {delete (*it);}}int main() {vector<Shape*> v;Shape* ps;ps = static_cast<Shape*>(DynObjectFactory::CreateObject("Circle"));v.push_back(ps);ps = static_cast<Shape*>(DynObjectFactory::CreateObject("Square"));v.push_back(ps);ps = static_cast<Shape*>(DynObjectFactory::CreateObject("Rectangle"));v.push_back(ps);DrawAllShapes(v);DeleteAllShapes(v);}

make.sh#!/bin/bashg++ Shape.cpp DynTest.cpp -o test -std=c++11