哈希表添加 - C

Question

在以下算法中获取一些段错误以将元素添加到哈希表中的正确存储桶。

我的结构是基本的：

struct kv {
    char* key;
    unsigned val;
    struct kv* next;
};

struct hashtable {
    struct kv** table;
    unsigned size;
}; 

还有我的越野车功能：

    struct kv* ht_find_or_put(char* word, unsigned value,
                                  struct hashtablet* hashtable,
                                  unsigned (*hash)(char*))
    {
        unsigned index = hash(word) % hashtable->size;
        struct kv* ke = malloc(sizeof (struct kv));

        for (ke = hashtable->table[index]; ke != NULL; ke = ke->next)
        {
            if (strcmp(ke->key, word) == 0)
                return ke;
        }

        if (ke == NULL)
        {
            ke->key = word;
            ke->val = value;
            ke->next = hashtable->table[index];
            hashtable->table[index] = ke;
        }
   return ke;
}

我知道我还没有添加所有测试（如果 malloc 失败等）只是试图调试这个特定问题......

我正在这样分配我的表：

struct hashtable* hashtable_malloc(unsigned size)
{
    struct hashtable *new_ht = malloc(sizeof(struct hashtable));
    new_ht->size = size;
    new_ht->table = malloc(sizeof(struct kv) * size);

    for(unsigned i = 0; i < size; i++)
        new_ht->table[i] = NULL;

    return new_ht;
}

我们将不胜感激任何形式的帮助。我才刚刚开始学习。

Answer 1

第一个问题是内存泄漏，例如- 您使用 malloc 分配内存，但在覆盖指针时会丢失对它的引用：

// allocate memory
struct kv* ke = malloc(sizeof (struct kv));
//   lose the reference
//   VVVVVVVVVVV
for (ke = hashtable->table[index]; ke != NULL; ke = ke->next)

可能导致段错误的第二个问题是您尝试取消引用空指针：

if (ke == NULL)
{
    // ke is NULL, you can't de-reference it
    ke->key = word;
    ke->val = value;
    ke->next = hashtable->table[index];
    hashtable->table[index] = ke;
}

解决方案是，恕我直言，仅在找不到新元素时分配和放置新元素：

struct kv* ht_find_or_put(char* word, unsigned value, struct hashtablet* hashtable, unsigned (*hash)(char*))
{
    unsigned index = hash(word) % hashtable->size;
    struct kv* ke;

    // first we try to find the node
    for (ke = hashtable->table[index]; ke != NULL; ke = ke->next)
    {
        if (strcmp(ke->key, word) == 0)
            return ke;
    }

    // didn't find it - lets create and put a new one.    
    if (ke == NULL)
    {
        ke = malloc(sizeof (struct kv));
        // later add a check if the allocation succeded...
        ke->key = word;
        ke->val = value;
        ke->next = hashtable->table[index];
        hashtable->table[index] = ke;
    }
    return ke;
}

由于我不想引入全新的代码，这会让你感到困惑，所以我对原始代码做了最小的改动。