我有以下结构：
typedef struct _chess {
int **array;
int size;
struct _chess *parent;
} chess;
我有：
typedef struct _chess *Chess;
现在，我想创建一个动态长度数组来存储指向ARCH结构的指针，所以我执行以下操作：
Chess array [] = malloc(size * sizeof(Chess));
这给我一个错误：初始化程序无效。
如果我放弃[]并执行此操作：
Chess array = malloc(size * sizeof(Chess));
它编译时没有错误但是当我尝试通过执行以下操作将此数组的元素设置为NULL时：
array[i]=NULL;
我收到错误：从类型'void *'
类型指定类型'struct _chess'时出现不兼容的类型知道我做错了什么吗？ 感谢。
答案 0 :(得分：39)
array是一个有点误导性的名字。对于动态分配的指针数组，malloc将返回指向内存块的指针。您需要使用Chess*而不是Chess[]来保存指向数组的指针。
Chess *array = malloc(size * sizeof(Chess));
array[i] = NULL;
也许稍后：
/* create new struct chess */
array[i] = malloc(sizeof(struct chess));
/* set up its members */
array[i]->size = 0;
/* etc. */
答案 1 :(得分：22)
这里有很多typedef。就个人而言，我反对“隐藏星号”，即typedef：将指针类型转换为看起来不像指针的东西。在C中，指针非常重要并且真正影响代码，foo和foo *之间存在很大差异。
我认为很多答案也对此感到困惑。
您分配了一组Chess值，这些值是指向chess类型值的指针（同样，非常令人困惑的命名法，我真的不能推荐）应该是这样的：
Chess *array = malloc(n * sizeof *array);
然后，您需要通过循环初始化实际实例：
for(i = 0; i < n; ++i)
array[i] = NULL;
这假设您不想为实例分配任何内存，您只需要一个指针数组，其中所有指针最初都指向任何内容。
如果你想分配空间，最简单的形式是：
for(i = 0; i < n; ++i)
array[i] = malloc(sizeof *array[i]);
了解sizeof用法100％一致，从不开始提及显式类型。 使用变量中固有的类型信息，让编译器担心哪种类型。不要重复自己。
当然，上面对malloc()进行了不必要的大量调用;根据使用模式，在计算所需的总大小之后，只需一次调用malloc()就可以完成上述所有操作。然后你仍然需要通过并初始化array[i]指针指向大块，当然。
答案 2 :(得分：1)
我同意上面的@maverik，我不想用typedef隐藏细节。特别是当你想要了解正在发生的事情时。我也更喜欢看一切而不是部分代码片段。话虽如此，这里是一个malloc并且没有复杂的结构。
该代码使用ms visual studio泄漏检测器，因此您可以尝试潜在的泄漏。
#include "stdafx.h"
#include <string.h>
#include "msc-lzw.h"
#define _CRTDBG_MAP_ALLOC
#include <stdlib.h>
#include <crtdbg.h>
// 32-bit version
int hash_fun(unsigned int key, int try_num, int max) {
return (key + try_num) % max; // the hash fun returns a number bounded by the number of slots.
}
// this hash table has
// key is int
// value is char buffer
struct key_value_pair {
int key; // use this field as the key
char *pValue; // use this field to store a variable length string
};
struct hash_table {
int max;
int number_of_elements;
struct key_value_pair **elements; // This is an array of pointers to mystruct objects
};
int hash_insert(struct key_value_pair *data, struct hash_table *hash_table) {
int try_num, hash;
int max_number_of_retries = hash_table->max;
if (hash_table->number_of_elements >= hash_table->max) {
return 0; // FULL
}
for (try_num = 0; try_num < max_number_of_retries; try_num++) {
hash = hash_fun(data->key, try_num, hash_table->max);
if (NULL == hash_table->elements[hash]) { // an unallocated slot
hash_table->elements[hash] = data;
hash_table->number_of_elements++;
return RC_OK;
}
}
return RC_ERROR;
}
// returns the corresponding key value pair struct
// If a value is not found, it returns null
//
// 32-bit version
struct key_value_pair *hash_retrieve(unsigned int key, struct hash_table *hash_table) {
unsigned int try_num, hash;
unsigned int max_number_of_retries = hash_table->max;
for (try_num = 0; try_num < max_number_of_retries; try_num++) {
hash = hash_fun(key, try_num, hash_table->max);
if (hash_table->elements[hash] == 0) {
return NULL; // Nothing found
}
if (hash_table->elements[hash]->key == key) {
return hash_table->elements[hash];
}
}
return NULL;
}
// Returns the number of keys in the dictionary
// The list of keys in the dictionary is returned as a parameter. It will need to be freed afterwards
int keys(struct hash_table *pHashTable, int **ppKeys) {
int num_keys = 0;
*ppKeys = (int *) malloc( pHashTable->number_of_elements * sizeof(int) );
for (int i = 0; i < pHashTable->max; i++) {
if (NULL != pHashTable->elements[i]) {
(*ppKeys)[num_keys] = pHashTable->elements[i]->key;
num_keys++;
}
}
return num_keys;
}
// The dictionary will need to be freed afterwards
int allocate_the_dictionary(struct hash_table *pHashTable) {
// Allocate the hash table slots
pHashTable->elements = (struct key_value_pair **) malloc(pHashTable->max * sizeof(struct key_value_pair)); // allocate max number of key_value_pair entries
for (int i = 0; i < pHashTable->max; i++) {
pHashTable->elements[i] = NULL;
}
// alloc all the slots
//struct key_value_pair *pa_slot;
//for (int i = 0; i < pHashTable->max; i++) {
// // all that he could see was babylon
// pa_slot = (struct key_value_pair *) malloc(sizeof(struct key_value_pair));
// if (NULL == pa_slot) {
// printf("alloc of slot failed\n");
// while (1);
// }
// pHashTable->elements[i] = pa_slot;
// pHashTable->elements[i]->key = 0;
//}
return RC_OK;
}
// This will make a dictionary entry where
// o key is an int
// o value is a character buffer
//
// The buffer in the key_value_pair will need to be freed afterwards
int make_dict_entry(int a_key, char * buffer, struct key_value_pair *pMyStruct) {
// determine the len of the buffer assuming it is a string
int len = strlen(buffer);
// alloc the buffer to hold the string
pMyStruct->pValue = (char *) malloc(len + 1); // add one for the null terminator byte
if (NULL == pMyStruct->pValue) {
printf("Failed to allocate the buffer for the dictionary string value.");
return RC_ERROR;
}
strcpy(pMyStruct->pValue, buffer);
pMyStruct->key = a_key;
return RC_OK;
}
// Assumes the hash table has already been allocated.
int add_key_val_pair_to_dict(struct hash_table *pHashTable, int key, char *pBuff) {
int rc;
struct key_value_pair *pKeyValuePair;
if (NULL == pHashTable) {
printf("Hash table is null.\n");
return RC_ERROR;
}
// Allocate the dictionary key value pair struct
pKeyValuePair = (struct key_value_pair *) malloc(sizeof(struct key_value_pair));
if (NULL == pKeyValuePair) {
printf("Failed to allocate key value pair struct.\n");
return RC_ERROR;
}
rc = make_dict_entry(key, pBuff, pKeyValuePair); // a_hash_table[1221] = "abba"
if (RC_ERROR == rc) {
printf("Failed to add buff to key value pair struct.\n");
return RC_ERROR;
}
rc = hash_insert(pKeyValuePair, pHashTable);
if (RC_ERROR == rc) {
printf("insert has failed!\n");
return RC_ERROR;
}
return RC_OK;
}
void dump_hash_table(struct hash_table *pHashTable) {
// Iterate the dictionary by keys
char * pValue;
struct key_value_pair *pMyStruct;
int *pKeyList;
int num_keys;
printf("i\tKey\tValue\n");
printf("-----------------------------\n");
num_keys = keys(pHashTable, &pKeyList);
for (int i = 0; i < num_keys; i++) {
pMyStruct = hash_retrieve(pKeyList[i], pHashTable);
pValue = pMyStruct->pValue;
printf("%d\t%d\t%s\n", i, pKeyList[i], pValue);
}
// Free the key list
free(pKeyList);
}
int main(int argc, char *argv[]) {
int rc;
int i;
struct hash_table a_hash_table;
a_hash_table.max = 20; // The dictionary can hold at most 20 entries.
a_hash_table.number_of_elements = 0; // The intial dictionary has 0 entries.
allocate_the_dictionary(&a_hash_table);
rc = add_key_val_pair_to_dict(&a_hash_table, 1221, "abba");
if (RC_ERROR == rc) {
printf("insert has failed!\n");
return RC_ERROR;
}
rc = add_key_val_pair_to_dict(&a_hash_table, 2211, "bbaa");
if (RC_ERROR == rc) {
printf("insert has failed!\n");
return RC_ERROR;
}
rc = add_key_val_pair_to_dict(&a_hash_table, 1122, "aabb");
if (RC_ERROR == rc) {
printf("insert has failed!\n");
return RC_ERROR;
}
rc = add_key_val_pair_to_dict(&a_hash_table, 2112, "baab");
if (RC_ERROR == rc) {
printf("insert has failed!\n");
return RC_ERROR;
}
rc = add_key_val_pair_to_dict(&a_hash_table, 1212, "abab");
if (RC_ERROR == rc) {
printf("insert has failed!\n");
return RC_ERROR;
}
rc = add_key_val_pair_to_dict(&a_hash_table, 2121, "baba");
if (RC_ERROR == rc) {
printf("insert has failed!\n");
return RC_ERROR;
}
// Iterate the dictionary by keys
dump_hash_table(&a_hash_table);
// Free the individual slots
for (i = 0; i < a_hash_table.max; i++) {
// all that he could see was babylon
if (NULL != a_hash_table.elements[i]) {
free(a_hash_table.elements[i]->pValue); // free the buffer in the struct
free(a_hash_table.elements[i]); // free the key_value_pair entry
a_hash_table.elements[i] = NULL;
}
}
// Free the overall dictionary
free(a_hash_table.elements);
_CrtDumpMemoryLeaks();
return 0;
}
答案 3 :(得分：0)
恕我直言，这看起来更好：
Chess *array = malloc(size * sizeof(Chess)); // array of pointers of size `size`
for ( int i =0; i < SOME_VALUE; ++i )
{
array[i] = (Chess) malloc(sizeof(Chess));
}