Hashtable Add

Question

获取以下算法的一些分段错误，以便在哈希表中向正确的桶中添加一个元素。

我的结构是基本的：

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

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

我的马车功能：

    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的测试(如果malloc失败的话)，只是尝试调试这个特定的问题.

我的桌子是这样分配的：

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;
}

任何形式的帮助都会受到极大的感谢。我才刚开始学。

Answer 1

第一个问题是内存泄漏，例如-您使用malloc分配内存，但是在覆盖指针时失去了对它的引用：

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

可能导致分段错误的第二个问题是，您试图取消引用一个空指针：

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;
}

解决办法是，只有在未能找到新元素的情况下，才分配和放置新元素：

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;
}

因为我不想引入全新的代码，这只会让您感到困惑，所以我对原始代码做了最小的修改。