Create objects dynamically
Without making any changes to the original class, it only needs to add a macro to realize dynamic creation.
macro
#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)
macro expansion
class CircleRegister
{
public:
static void* NewInstance()
{
return new Circle;
}
private:
static Register reg_;//声明
}
Register CircleRegister::reg_("Circle",CircleRegister::NewInstance)
Shape.h
#pragma once
#include <iostream>
#include <vector>
using namespace std;
class Shape
{
public:
virtual void Draw() = 0;
virtual ~Shape() {
};
};
class Circle :public Shape
{
public:
void Draw();
~Circle();
};
class Square :public Shape
{
public:
void Draw();
~Square();
};
class Rectangle :public Shape
{
public:
void Draw();
~Rectangle();
};
Shape.cpp
#include "Shape.h"
#include <iostream>
#include <vector>
#include "DynObjectFactory.h"
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);
/*宏展开
class CircleRegister
{
public:
static void* NewInstance()
{
return new Circle;
}
private:
static Register reg_;//声明
}
Register CircleRegister::reg_("Circle",CircleRegister::NewInstance)
*/
/*宏
#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)
*/
DynObjectFactory.h
#pragma once
#include <iostream>
#include <string>
#include <map>
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 0;
else
return it->second();
}
static void Register(const string& name, CREATE_FUNC func)
{
mapCls_[name] = func;
}
private:
static map<string, CREATE_FUNC> mapCls_;
};
//g++
//__attribute((weak))
_declspec(selectany) 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)
DynObjectFactory.cpp
#include "DynObjectFactory.h"
#include <iostream>
#include <vector>
#include "Shape.h"
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);
return 0;
}