一种hashmap的简单实现

//template <class T>
//利用id来索引到对应的对象
struct HashNode {
    int id;
    void* obj;
    struct list_head list_item;
}

struct list_head {
    list_head* prev;
    list_head* next;
}
#define LIST_HEAD_INIT(name) { &(name), &(name) }
#define INIT_LIST_HEAD(ptr) do { (ptr)->next = (ptr); (ptr)->prev = (ptr); } while (0)
#define list_for_each(pos, head) for (pos = (head)->next; pos != (head); pos = pos->next)
#define list_for_each_safe(pos, n, head) for (pos = (head)->next, n = pos->next; pos != (head); pos = n, n = pos->next)
static inline void list_add(struct list_head *p,
                              struct list_head *prev,
                              struct list_head *next)
{
    next->prev = p;
    p->next = next;
    p->prev = prev;
    prev->next = p;
}
static inline void list_add_in(struct list_head *p, struct list_head *head)
{
    list_add(p, head, head->next);
}
static inline void list_add_tail(struct list_head *p, struct list_head *head)
{
    list_add(p, head->prev, head);
}
static inline void __list_del(struct list_head *prev, struct list_head *next)
{
    next->prev = prev;
    prev->next = next;
}
static inline void list_del(struct list_head *entry)
{
    __list_del(entry->prev, entry->next);
    entry->next = 0;
    entry->prev = 0;
}


#ifndef offsetof
#if __GNUC__ >= 4

#define offsetof(type, member)  __builtin_offsetof (type, member);printf("this is gcc > 4\n");
#else
#define offsetof(type, member) (unsigned long)(&((type *)0)->member);printf("this is gcc < 4\n");
#endif
#endif

#define list_entry(ptr, type, member) ((type *)((char *)(ptr)-offsetof(type, member)))

class CHashMap {
private:
    struct HashNode* hash_table;
    int hash_table_size;

public:
    CHashMap();
    ~CHashMap();
    int CreateMap(int map_size);
    int AddMapObj(int id, void* obj);
    int DelMapObj(int id);
    void* GetMapObj(int id);
    int ClearMap();    
}

CHashMap() {
    hash_table = NULL;
    hash_table_size = 0;
}
~CHashMap() {
    if (hash_table) {
        ClearMap();
    }
    hash_table_size = 0;
}
int CreateMap(int map_size) {
    try {
        hash_table = new HashNode[map_size];
    } catch(&bad_alloc) {
        return -1;
    }
    //对每个hash桶的头节点进行初始化
    for (int i = 0; i < map_size; i++) {
        hash_table[i].id = 0;
        hash_table[i].obj = NULL;
        INIT_LIST_HEAD(&hash_table[i].list_item);
    }
    hash_table_size = map_size;
    return 0;
}

int AddMapObj(int id, void* obj) {
    int bucket_id = id%hash_table_size;
    HashNode* temp = new struct HashNode();
    temp->id = id;
    temp->obj = obj;
    list_add_tail(&temp->list_item, &hash_table[bucket_id].list_item);
    return 0;
}
int DelMapObj(int id)
{
    int bucket_id = id%hash_table_size;
    struct list_head* temp1;
    struct list_head* temp2;
    struct list_head* head = &hash_table[bucket_id].list_item;
    struct HashNode* node;
    
    list_for_each_safe(temp1, temp2, head)
    {
        node = list_entry(temp1, struct HashNode, list_item);
        if (node->id == id)
        {
            list_del(temp1);
            delete node;
            return 0;
        }
    }
    return -1;
    
}
void* GetMapObj(int id) {
    int bucket_id = id%hash_table_size;
    struct list_head* head = &hash_table[bucket_id].list_item;
    struct list_head* temp ;
    struct HashNode* node;
    list_for_each(temp, head)
    {
        node = list_entry(temp, struct HashNode, list_item);
        if (node->id == id) {
            return node->obj;
        }
    }
    return NULL;
}
int ClearMap()
{
    struct list_head* _head;
    struct list_head* _tmp1;
    struct list_head* _tmp2;
    struct OBJECTMAP*  item;

    for( int i=0; i<hash_table_size; i++ )
    {
        _head = &hash_table[i].list_item;    //head节点并没有存储数据，不需要析构
        list_for_each_safe(_tmp1,_tmp2,_head)
        {
            item = list_entry(_tmp1,struct OBJECTMAP,list_item);
            list_del(_tmp1);
            delete item;
        }
    }

    delete[] hash_table;
    hash_table = NULL;
    hash_table_size = 0;

    return 0;
}

template<typename  NodeType>
struct HashListNode
{
    NodeType obj;
    struct list_head list_item;
};
template<typename  NodeType, typename Traits>
int idx =  Traits::GetNodeID(obj)% hash_table_size;