如何在程序中加载各个模块（也谈C++多态的威力）

        在一个大型项目或工程中， 经常包含很多模块。 通常而言， 当系统开启的时候， 需要加载各个模块， 下面我们提供一种方法， 顺便看看C++中多态的威力：

#include <iostream>
using namespace std;

// 基础模块
class BASIC_MOD
{
public:
virtual void start() // 虚函数。 如果没有virtual, 那么则不能正确加载各个模块
{
cout << "BASIC_MOD" << endl;
}
};

// 模块1， 继承基础模块
class MOD1 : public BASIC_MOD
{
public:
static MOD1 *getInstance()
{
static MOD1* pInstance = NULL;
if(NULL == pInstance)
{
pInstance = new MOD1; // 单例
}

return pInstance;
}

// 模块1启动
void start()
{
cout << "MOD1 is starting..." << endl;
}
};

class MOD2 : public BASIC_MOD
{
public:
static MOD2 *getInstance()
{
static MOD2* pInstance = NULL;
if(NULL == pInstance)
{
pInstance = new MOD2;
}

return pInstance;
}

void start()
{
cout << "MOD2 is starting..." << endl;
}
};

class MOD3 : public BASIC_MOD
{
public:
static MOD3 *getInstance()
{
static MOD3* pInstance = NULL;
if(NULL == pInstance)
{
pInstance = new MOD3;
}

return pInstance;
}

void start()
{
cout << "MOD3 is starting..." << endl;
}
};

class MOD4 : public BASIC_MOD
{
public:
static MOD4 *getInstance()
{
static MOD4* pInstance = NULL;
if(NULL == pInstance)
{
pInstance = new MOD4;
}

return pInstance;
}

void start()
{
cout << "MOD4 is starting..." << endl;
}
};

class MOD5 : public BASIC_MOD
{
public:
static MOD5 *getInstance()
{
static MOD5* pInstance = NULL;
if(NULL == pInstance)
{
pInstance = new MOD5;
}

return pInstance;
}

void start()
{
cout << "MOD5 is starting..." << endl;
}
};

class MOD6 : public BASIC_MOD
{
public:
static MOD6 *getInstance()
{
static MOD6* pInstance = NULL;
if(NULL == pInstance)
{
pInstance = new MOD6;
}

return pInstance;
}

void start()
{
cout << "MOD6 is starting..." << endl;
}
};

BASIC_MOD* mod[] =
{
MOD1::getInstance(),
MOD2::getInstance(),
MOD3::getInstance(),
MOD4::getInstance(),
MOD5::getInstance(),
MOD6::getInstance(), // 最后这个逗号可要可不要， 但最好加上， 方面其他人增加模块
};

int main()
{
int size = sizeof(mod) / sizeof(mod[0]);
int i = 0;
for(i = 0; i < size; i++)
{
mod[i]->start(); // 一种接口， 多种实现， 启动所有模块
}

return 0;
}

      结果

：

MOD1 is starting...

MOD2 is starting...

MOD3 is starting...

MOD4 is starting...

MOD5 is starting...

MOD6 is starting...