本文介绍了如何在C语言中实现一个简单的字典数据结构，包括哈希表的定义、哈希函数、查找和安装功能。此外，还提供了字典操作的接口，如插入键值对和获取键对应的值。
/////////// C dictionary data structure ////////////
struct nlist { /* table entry: */
struct nlist *next; /* next entry in chain */
char *name; /* defined name */
char *defn; /* replacement text */
};
#define HASHSIZE 101
static struct nlist *hashtab[HASHSIZE]; /* pointer table */
/* hash: form hash value for string s */
unsigned hash(char *s)
{
unsigned hashval;
for (hashval = 0; *s != '\0'; s++)
hashval = *s + 31 * hashval;
return hashval % HASHSIZE;
}
/* lookup: look for s in hashtab */
struct nlist *lookup(char *s)
{
struct nlist *np;
for (np = hashtab[hash(s)]; np != NULL; np = np->next)
if (strcmp(s, np->name) == 0)
return np; /* found */
return NULL; /* not found */
}
char *strdup(char *);
/* install: put (name, defn) in hashtab */
struct nlist *install(char *name, char *defn)
{
struct nlist *np;
unsigned hashval;
if ((np = lookup(name)) == NULL) { /* not found */
np = (struct nlist *) malloc(sizeof(*np));
if (np == NULL || (np->name = strdup(name)) == NULL)
return NULL;
hashval = hash(name);
np->next = hashtab[hashval];
hashtab[hashval] = np;
} else /* already there */
free((void *) np->defn); /*free previous defn */
if ((np->defn = strdup(defn)) == NULL)
return NULL;
return np;
}
char *strdup(char *s) /* make a duplicate of s */
{
char *p;
p = (char *) malloc(strlen(s)+1); /* +1 for ’\0’ */
if (p != NULL)
strcpy(p, s);
return p;
}
/*dic opreation interface */
void dic_put(char *key, char *value)
{
install(key,value);
}
char* dic_value_for_key(char *key)
{
char *ret = "";
struct nlist *np = lookup(key);
if (np != NULL) {
ret = np->defn;
}
return ret;
}
/////////// C dictionary data structure end ////////////
============= 调用例子 =================
dic_put("1", "Hello");
printf("value ====>> %s\n", dic_value_for_key("1"));
输出:
value ====>> Hello
=======================================
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