命名空间使用后，在头文件中怎样声明？

关于c++类的前置声明，这里有篇文章比较好。

http://software.intel.com/zh-cn/blogs/2010/05/04/c-2/?cid=sw:prccsdn1073

 

还有篇类对象数组初始化的三种方法

http://blog.chinaunix.net/u2/84086/showart_1892055.html

这里有个简单例子

 

车与轮子

 

car.h

#ifndef __Car_H__ #define __Car_H__ class Wheel; class Car { public: Car(int num); ~Car(); void show(); private: Wheel* mWheel; int mWheelNum; }; #endif

 

wheel.h

 

#ifndef __Wheel_H__ #define __Wheel_H__ #include <iostream> using namespace std; class Wheel { public: Wheel(); ~Wheel(); void show(); }; #endif

 

wheel.cpp

 

#include "Wheel.h" Wheel::Wheel() { cout << "Wheel is created" << endl; } Wheel::~Wheel() { cout << "Wheel is destroyed" << endl; } void Wheel::show() { }

 

car.cpp

#include "Car.h" #include "Wheel.h" Car::Car(int num) { cout << "car is created" << endl; mWheel = new Wheel[num]; } Car::~Car() { cout << "car is destroyed" << endl; delete[] mWheel; } void Car::show() { }

---

如果加入了命名空间，怎么写类声明呢？

 

1.如果类都在同一命名空间，那直接写在同一namespace里面就可以了

 

wheel.h

#ifndef __Wheel_H__ #define __Wheel_H__ #include <iostream> using namespace std; namespace Gnuser { class Wheel { public: Wheel(); ~Wheel(); void show(); }; } #endif

 

car.h

#ifndef __Car_H__ #define __Car_H__ namespace Gnuser { class Wheel; class Car { public: Car(int num); ~Car(); void show(); private: Wheel* mWheel; int mWheelNum; }; } #endif

 

2. 现在如果再加一个命名空间，那么可以这样定义

#ifndef __Road_H__ #define __Road_H__ #include <vector> using namespace std; namespace Gnuser { class Car; } namespace Dxn { class Road { public: Road(int num); ~Road(); void addCar(); private: vector<Gnuser::Car*> mCars; }; } #endif