用C語言實現一個簡單實用的hashmap，具有一定的實際意義。尤其我們不想使用STL裡面的map<...>類的時候。我實現的這個hashmap，用來做key---value的映射，key必須是有效的字符串，value是調用者分配的任意類型的數據。這個hashmap適合在一些簡單的場合下，消耗極少的資源。
首先定義頭文件如下：
/*
* hashmap.h
* Generic hash map: key(string)-value(any type).
* cheungmine
* Sep. 22, 2007. All rights reserved.
*/
#ifndef HASHMAP_H_INCLUDED
#define HASHMAP_H_INCLUDED
#include "unistd.h"
/* You should always use 1024 */
#define HASHMAP_SIZE 1024
/* Opaque struct pointer to _hash_map_t */
typedef struct _hash_map_t* hash_map;
typedef void(*pfcb_hmap_value_free)(void* value);
/* An example of free value function implemented by caller:
void my_hmap_free_value(void* pv)
{
free(pv);
}
*/
/* Create before use. eg:
* hash_map hm;
* hmap_create (&hm, HASHMAP_SIZE);
* assert (hm); // out of memory if hm==NULL
* void* mydata=malloc(n);
* hmap_insert(hm, "shanghai", -1, mydata);
...
* hmap_destroy(hm, my_hmap_free_value);
*/
extern void
hmap_create(hash_map *hmap, int size);
/* Destroy after use */
extern void
hmap_destroy(hash_map hmap, pfcb_hmap_value_free);
/* Insert a key-value into hash map. value is a pointer to callee-allocated memory */
extern void
hmap_insert(hash_map hmap, const char* key, int key_len/* -1 for strlen to be called */, void* value);
/* Search a hash map for value of given key string */
extern void*
hmap_search(hash_map hmap, const char *key);
#endif /* HASHMAP_H_INCLUDED */
實現文件如下：
/*
* hashmap.c
* Generic hashmap implementation.
* a map for pair of key-value. key must be a null-end string, value is any type of data.
* cheungmine
* Sep. 22, 2007. All rights reserved.
*/
#include "hashmap.h"
#include "list.h"
typedef struct _hash_map_t
{
size_t size;
listnode_t** key;
listnode_t** value;
}hash_map_t;
/* Hash a string, return a hash key */
static ulong hash_string(const char *s, int len)
{
ulong h = 0;
int i = 0;
assert (s);
if (len < 0)
len = (s? (int)strlen(s): 0);
while(i++ < len) { h = 17*h + *s++; }
return h;
}
static void _free_map_key(listnode_t* node)
{
listnode_t *old;
while(node)
{
old = node;
node = node->next;
free(old->data);
free (old);
}
}
static void _free_map_value(listnode_t* node, pfcb_hmap_value_free pfunc)
{
listnode_t *old;
while(node)
{
old = node;
node = node->next;
if (pfunc)
(*pfunc)(old->data);
free (old);
}
}
/*=============================================================================
Public Functions
=============================================================================*/
/* Create before use */
void
hmap_create(hash_map *hmap, int size)
{
(*hmap) = (hash_map_t*) malloc(sizeof(hash_map_t));
(*hmap)->size = size;
(*hmap)->key = (listnode_t**) calloc(size, sizeof(listnode_t*));
(*hmap)->value = (listnode_t**) calloc(size, sizeof(listnode_t*));
}
/* Destroy after use */
extern void
hmap_destroy(hash_map hmap, pfcb_hmap_value_free pfunc)
{
size_t i;
for(i=0; i<hmap->size; i++){
_free_map_key(hmap->key[i]);
_free_map_value(hmap->value[i], pfunc);
}
free(hmap->key);
free(hmap->value);
free(hmap);
}
/* Insert a key-value into hash map. value is a pointer to callee-allocated memory */
void
hmap_insert(hash_map hmap, const char* key, int key_len, void* value)
{
listnode_t *node_key, *node_val;
ulong h;
char *s;
assert (key);
if (key_len<0) key_len = (int) strlen (key);
s = (char*) malloc (key_len+1);
assert(s);
#pragma warning(push) /* C4996 */
#pragma warning( disable : 4996 )
strncpy (s, key, key_len);
#pragma warning(pop) /* C4996 */
s[key_len] = 0;
node_key = list_node_create ( (void*)s );
node_val = list_node_create ( value );
assert(node_key && node_val);
h = hash_string (s, key_len) % hmap->size;
node_key->next = hmap->key[h];
hmap->key[h] = node_key;
node_val->next = hmap->value[h];
hmap->value[h] = node_val;
}
/* Search a hash map for value of given key string */
void*
hmap_search(hash_map hmap, const char *key)
{
ulong h = hash_string (key, -1) % hmap->size;
listnode_t *pk = hmap->key[h];
listnode_t *pv = hmap->value[h];
while (pk)
{
if (strcmp(key, pk->str) == 0)
return pv->data;
pk = pk->next;
pv = pv->next;
}
return NULL;
}
好了，其中用到的其他文件（unistd.h，list.h，list.c）看我下一篇文章！
C語言實現一個簡單的單向鏈表list
