C 字典实现

/////////// 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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