#include <iostream>
#include <string>
using namespace std;class airplanerep  // 表示一个飞机对象
{
public:airplanerep(int id,const string & s,const string & d){ID = id;start = s;dest = d;}~airplanerep(){cout<<"airplanerep destructor!"<<endl;}int getID() const{return ID;}private:int ID;string start;string dest;
};// 注意airplane和airplanerep含有一样的成员函数，它们的接口完全相同
// 类airplane实际上是个句炳类(Handle class)
class airplane // 修改后的类 — 支持自定义的内存管理
{
public:airplane(int id,const string & s,const string & d){rep = new airplanerep(id,s,d);}~airplane(){delete rep;}int getID() const{return rep->getID();}static void * operator new(size_t size);static void operator delete(void *deadobject,size_t size);private:union{airplanerep *rep;  // 用于被使用的对象airplane *next;    // 用于没被使用的（在自由链表中）对象
    };// 类的常量，指定一个大的内存块中放多少个// airplane对象，在后面初始化static const int block_size;static airplane *headoffreelist;
};airplane *airplane::headoffreelist; //内存池链表头
const int airplane::block_size = 512; //内存池块的个数void * airplane::operator new(size_t size)
{// 把“错误”大小的请求转给::operator new()处理;if(size != sizeof(airplane))return ::operator new(size);airplane *p = headoffreelist; // p指向自由链表的表头// p 若合法，则将表头移动到它的下一个元素if(p)headoffreelist = p->next;else{// 自由链表为空，则分配一个大的内存块，// 可以容纳block_size个airplane对象airplane *newblock = static_cast<airplane*>(::operator new(block_size * sizeof(airplane)));// 将每个小内存块链接起来形成一个新的自由链表// 跳过第0个元素，因为它要被返回给operator new的调用者for (int i = 1; i < block_size-1; ++i)newblock[i].next = &newblock[i+1];// 用空指针结束链表newblock[block_size-1].next = 0;// p 设为表的头部，headoffreelist指向的// 内存块紧跟其后p = newblock;headoffreelist = &newblock[1];}return p;
}// 传给operator delete的是一个内存块, 如果
// 其大小正确，就加到自由内存块链表的最前面
void airplane::operator delete(void *deadobject,size_t size)
{if(deadobject == 0) return;if(size != sizeof(airplane)){::operator delete(deadobject);return;}//将要释放的空间插入空闲区链表前端airplane *carcass = static_cast<airplane*>(deadobject);carcass->next = headoffreelist;headoffreelist = carcass;
}int main()
{airplane *pa = new airplane(101,"shanghai","beijing"); // 第一次分配: 得到大块内存，生成自由链表，等cout<<pa->getID()<<endl;delete pa;airplane *pb = new airplane(102,"shanghai","beijing");cout<<pb->getID()<<endl;delete pb;return 0;
}

template<class T>
class CachedObj
{
public:void * operator new(size_t sz);void operator delete(void* p, size_t sz);virtual ~CachedObj() {}
protected:T * next;
private:static void add_to_freelist(T * p);static allocator<T> alloc_mem;static T * free_store;static const size_t chunk;
};template<class T>
allocator<T> CachedObj<T>::alloc_mem;template<class T>
T* CachedObj<T>::free_store = NULL;template<class T>
const size_t CachedObj<T>::chunk = 64;template<class T>
void *CachedObj<T>::operator new(size_t sz)
{if(sz != sizeof(T))return ::operator new(sz);if (!free_store){T * array = alloc_mem.allocate(chunk);for(size_t i = 0; i != chunk; ++i)add_to_freelist(&array[i]);}T *p = free_store;free_store = free_store->next;return p;
}template<class T>
void CachedObj<T>::operator delete(void * p,size_t sz)
{if(p == NULL) return;if(sz != sizeof(T)){::operator delete(p);return;}add_to_freelist(static_cast<T*>(p));
}template<class T>
void CachedObj<T>::add_to_freelist(T *p)
{p->next = free_store;free_store = p;
}

// 表示一个飞机对象
class airplanerep: public CachedObj<airplanerep>
{
public:airplanerep(int id,const string & s,const string & d){ID = id;start = s;dest = d;}~airplanerep(){cout<<"airplanerep destructor!"<<endl;}int getID() const{return ID;}private:int ID;string start;string dest;
};int main()
{airplanerep *pa = new airplanerep(101,"shanghai","beijing");cout<<pa->getID()<<endl;delete pa;airplanerep *pb = new airplanerep(102,"shanghai","beijing");cout<<pb->getID()<<endl;delete pb;return 0;
}