c - uthash 将新条目添加到 HashMap

Question

我想用 uthash 创建一个 HashMap .

我希望键和值是一个结构体，包含一个 String 和一个 size_t ，如下所示:

typedef struct hash_ptr {
    char* string;
    size_t len;
}hash_ptr;

哈希表本身如下所示:

typedef struct hash_map_entry {
    struct hash_ptr *key;
    struct hash_ptr *value;
    UT_hash_handle hh;
}hash_map_entry;

为了向 map 添加新条目，我编写了一个名为 add_entry() 的新函数:

void add_entry(hash_map_entry *map, hash_ptr *key, hash_ptr *value) {
    hash_map_entry *entry;
    HASH_FIND(hh, map, key, sizeof *key, entry);
    if (entry == NULL) {
        entry = (hash_map_entry*) malloc(sizeof *entry);
        memset(entry, 0, sizeof *entry);
        entry->value = value;
        entry->key = key;
        HASH_ADD(hh, map, key, sizeof *key, entry);
    }
}

但是，在初始化并调用add_entry()之后...

hash_map_entry *map = NULL;

hash_ptr *key = (hash_ptr*) malloc(sizeof *key);
memset(key, 0, sizeof *key);
key->string = "Is this the Krusty Krab?";
key->len = strlen(key->string);

hash_ptr *value = (hash_ptr*) malloc(sizeof *value);
memset(value, 0, sizeof *value);
value->string = "No, this is Patrick!";
value->len = strlen(value->string);

add_entry(map, key, value);

...HASH_FIND 未找到添加的条目:

hash_map_entry *find_me;
HASH_FIND(hh, map, key, sizeof *key, find_me);

find_me 为 NULL。

我遵循 official user guide 中使用结构作为键的说明.

我哪里错了？

Answer 1

这是我能想到的最简单的修改。与原来相比的变化是:

1. 将 add_entry 的第一个参数从 hash_map_entry *map 更改为 hash_map_entry **map 并相应调整代码。

2. 使用HASH_ADD_KEYPTR对struct hash_ptr内的字符串内容进行散列，而不是对struct hash_ptr本身进行散列。注意:代码假定len成员是string成员指向的对象的长度，以字节为单位。

3. 与2相关，更改HASH_FIND的用法，对struct hash_ptr内的字符串内容进行哈希处理。

结果如下:

#include <stdio.h>
#include <stdlib.h>
#include "uthash.h"

typedef struct hash_ptr {
    char* string;
    size_t len;
}hash_ptr;

typedef struct hash_map_entry {
    struct hash_ptr *key;
    struct hash_ptr *value;
    UT_hash_handle hh;
}hash_map_entry;

void add_entry(hash_map_entry **map, hash_ptr *key, hash_ptr *value) {
    hash_map_entry *entry;
    HASH_FIND(hh, *map, key->string, key->len, entry);
    if (entry == NULL) {
        entry = (hash_map_entry*) malloc(sizeof *entry);
        memset(entry, 0, sizeof *entry);
        entry->value = value;
        entry->key = key;
        HASH_ADD_KEYPTR(hh, *map, key->string, key->len, entry);
    }
}

int main(void)
{
    hash_map_entry *map = NULL;

    hash_ptr *key = (hash_ptr*) malloc(sizeof *key);
    memset(key, 0, sizeof *key);
    key->string = "Is this the Krusty Krab?";
    key->len = strlen(key->string);

    hash_ptr *value = (hash_ptr*) malloc(sizeof *value);
    memset(value, 0, sizeof *value);
    value->string = "No, this is Patrick!";
    value->len = strlen(value->string);

    add_entry(&map, key, value);

    hash_map_entry *find_me;
    HASH_FIND(hh, map, key->string, key->len, find_me);
    if (find_me)
    {
        printf("found key=\"%s\", val=\"%s\"\n", find_me->key->string, find_me->value->string);
    }
    else
    {
        printf("not found\n");
    }
    return 0;
}