C 哈希表插入和查找的指针问题
我正在使用来自github的数据结构的自定义C实现。此处的文档: 这是我第一次使用这种低级哈希表,当我恢复以前插入的值时,我遇到了一些指针问题 我的代码只是一个简单的测试,只需要插入和恢复数据C 哈希表插入和查找的指针问题,c,hashtable,C,Hashtable,我正在使用来自github的数据结构的自定义C实现。此处的文档: 这是我第一次使用这种低级哈希表,当我恢复以前插入的值时,我遇到了一些指针问题 我的代码只是一个简单的测试,只需要插入和恢复数据 #include "list.h" #include "hash-table.h" #include <stdio.h> //typedef unsigned int (*HashTableHashFunc)(HashTableKey value); unsigned int hashFun
#include "list.h"
#include "hash-table.h"
#include <stdio.h>
//typedef unsigned int (*HashTableHashFunc)(HashTableKey value);
unsigned int hashFunc(HashTableKey v_key)
{
unsigned int *key = (unsigned int *)v_key;
return *key % 20;
}
//typedef int (*HashTableEqualFunc)(HashTableKey value1, HashTableKey value2);
int equalFunc(HashTableKey value1, HashTableKey value2)
{
int *key1 = (int *)value1;
int *key2 = (int *)value2;
return *key1 == *key2;
}
int main(int argc, char const *argv[])
{
HashTable *mapMatrices;
//ListEntry *posicionListaPeticiones;
mapMatrices = hash_table_new(hashFunc, equalFunc);
for (int i = 0; i < 10; i++)
{
int key = i;
int value = i * 200;
int stat = hash_table_insert(mapMatrices, &key, &value);
if (!stat)
printf("Error inserting key %i with value %i\n", key, value);
else
printf("Inserted key %i with value %i\n", key, value);
}
for (int i = 0; i < 10; i++)
{
int key = i;
void *v_value = hash_table_lookup(mapMatrices, &key);
int value = *(int *)v_value;
printf("Key pointer %x : Value pointer %x\n", &key, &value);
}
}
这就是我试图打印地址内容后发生的情况
Inserted key 0 with value 0
Inserted key 1 with value 200
Inserted key 2 with value 400
Inserted key 3 with value 600
Inserted key 4 with value 800
Inserted key 5 with value 1000
Inserted key 6 with value 1200
Inserted key 7 with value 1400
Inserted key 8 with value 1600
Inserted key 9 with value 1800
Key ed75a354 : Value pointer ed75a358
Key ed75a354 : Value pointer ed75a358
Key ed75a354 : Value pointer ed75a358
Key ed75a354 : Value pointer ed75a358
Key ed75a354 : Value pointer ed75a358
Key ed75a354 : Value pointer ed75a358
Key ed75a354 : Value pointer ed75a358
Key ed75a354 : Value pointer ed75a358
Key ed75a354 : Value pointer ed75a358
Key ed75a354 : Value pointer ed75a358
printf("Key %i : Value pointer %i\n", key, value);
哈希表的实现代码
HashTable *hash_table_new(HashTableHashFunc hash_func,
HashTableEqualFunc equal_func)
{
HashTable *hash_table;
/* Allocate a new hash table structure */
hash_table = (HashTable *) malloc(sizeof(HashTable));
if (hash_table == NULL) {
return NULL;
}
hash_table->hash_func = hash_func;
hash_table->equal_func = equal_func;
hash_table->key_free_func = NULL;
hash_table->value_free_func = NULL;
hash_table->entries = 0;
hash_table->prime_index = 0;
/* Allocate the table */
if (!hash_table_allocate_table(hash_table)) {
free(hash_table);
return NULL;
}
return hash_table;
}
int hash_table_insert(HashTable *hash_table, HashTableKey key,
HashTableValue value)
{
HashTableEntry *rover;
HashTablePair *pair;
HashTableEntry *newentry;
unsigned int index;
/* If there are too many items in the table with respect to the table
* size, the number of hash collisions increases and performance
* decreases. Enlarge the table size to prevent this happening */
if ((hash_table->entries * 3) / hash_table->table_size > 0) {
/* Table is more than 1/3 full */
if (!hash_table_enlarge(hash_table)) {
/* Failed to enlarge the table */
return 0;
}
}
/* Generate the hash of the key and hence the index into the table */
index = hash_table->hash_func(key) % hash_table->table_size;
/* Traverse the chain at this location and look for an existing
* entry with the same key */
rover = hash_table->table[index];
while (rover != NULL) {
/* Fetch rover's HashTablePair entry */
pair = &(rover->pair);
if (hash_table->equal_func(pair->key, key) != 0) {
/* Same key: overwrite this entry with new data */
/* If there is a value free function, free the old data
* before adding in the new data */
if (hash_table->value_free_func != NULL) {
hash_table->value_free_func(pair->value);
}
/* Same with the key: use the new key value and free
* the old one */
if (hash_table->key_free_func != NULL) {
hash_table->key_free_func(pair->key);
}
pair->key = key;
pair->value = value;
/* Finished */
return 1;
}
rover = rover->next;
}
/* Not in the hash table yet. Create a new entry */
newentry = (HashTableEntry *) malloc(sizeof(HashTableEntry));
if (newentry == NULL) {
return 0;
}
newentry->pair.key = key;
newentry->pair.value = value;
/* Link into the list */
newentry->next = hash_table->table[index];
hash_table->table[index] = newentry;
/* Maintain the count of the number of entries */
++hash_table->entries;
/* Added successfully */
return 1;
}
HashTableValue hash_table_lookup(HashTable *hash_table, HashTableKey key)
{
HashTableEntry *rover;
HashTablePair *pair;
unsigned int index;
/* Generate the hash of the key and hence the index into the table */
index = hash_table->hash_func(key) % hash_table->table_size;
/* Walk the chain at this index until the corresponding entry is
* found */
rover = hash_table->table[index];
while (rover != NULL) {
pair = &(rover->pair);
if (hash_table->equal_func(key, pair->key) != 0) {
/* Found the entry. Return the data. */
return pair->value;
}
rover = rover->next;
}
/* Not found */
return HASH_TABLE_NULL;
}
你对指针有些困惑。 如果更换:
for (int i = 0; ...
与
对于主回路中的第一个回路,以及:
对于i=0
在第二个循环中,您将获得预期的输出
如果将此行添加到equalFunc:
fprintf(stderr,"cmp %p/%d, %p/%d\n", key1, *key1, key2, *key2);
您会注意到equalFunc的两个参数总是相同的——它们实际上指向您的局部“i”变量。
这就是为什么这不适用于两个独立的“i”值
带有调试器的Moment将显示:
void *v_value = hash_table_lookup(mapMatrices, &i);
在源中返回NULL[即未找到],但您仍可以继续并取消引用它
为了使程序正确,您可能应该按值传递密钥,而不是引用:
int stat = hash_table_insert(mapMatrices, (int *)i, (int *)value);
...
void *v_value = hash_table_lookup(mapMatrices, (int *)i);
int value = (int )v_value;
...
/* equalFunc: */
return (int)value1 == (int)value2;
但是出于卫生原因,使用内部和外部的石膏,不要让行为不明确的邪恶之神烧毁你的家。你预计会发生什么?key和value都是局部变量,它们的地址在循环中不会改变。你希望他们的地址会改变吗?我刚刚添加了更多关于我的指纹的信息,显示了真正的错误。很抱歉,我之前的帖子打印时出现seg故障意味着某些内存被覆盖和损坏。不幸的是,破坏内存的写操作是允许的,并且在实际发生写操作的地方不会出现seg错误。从这里,您可以尝试使用valgrind之类的工具,也可以仔细检查所有类型和调用。例如,hash_table_new需要一个HashTableHashFunc,它应该返回一个long,但是您给hash_table_new的函数返回一个int。这个错误只会由于截断而导致错误的哈希插入,而不是seg错误。谢谢,这帮助我解决了我的问题,更好地理解了C指针。
void *v_value = hash_table_lookup(mapMatrices, &i);
int stat = hash_table_insert(mapMatrices, (int *)i, (int *)value);
...
void *v_value = hash_table_lookup(mapMatrices, (int *)i);
int value = (int )v_value;
...
/* equalFunc: */
return (int)value1 == (int)value2;