C中的关联数组

Question

我正在实现一种将一组数据传输到可编程加密狗的方法.加密狗基于智能卡技术,可以在内部执行任意代码.输入和输出数据作为二进制块传递,可通过输入和输出指针访问.

我想使用关联数组来简化数据处理代码.一切都应该这样:

首先是主机应用程序:

// Host application in C++
in_data["method"] = "calc_r";
in_data["id"] = 12;
in_data["loc_a"] = 56.19;
in_data["loc_l"] = 44.02;
processor->send(in_data);

接下来加密狗内的代码:

// Some dongle function in C
char* method_name = assoc_get_string(in_data, "method");
int id = assoc_get_int(in_data, "id");
float loc_a = assoc_get_float(in_data, "loc_a");
float loc_l = assoc_get_float(in_data, "loc_l");

所以我的问题是关于加密狗部分的功能.是否有C代码或库来实现如上所述的关联数组行为？

Answer 1

Glib的哈希表.实现一个map接口或(关联数组).而且它最有可能是C最常用的哈希表实现.

GHashTable *table=g_hash_table_new(g_str_hash, g_str_equal);

/* put */
g_hash_table_insert(table,"SOME_KEY","SOME_VALUE");

/* get */
gchar *value = (gchar *) g_hash_table_lookup(table,"SOME_KEY");

Answer 2

我怀疑你必须写自己的.如果我理解您所描述的架构,那么您将需要将整个数据块一起发送.如果是这样,那么大多数库都不适用于它,因为它们很可能会分配多个内存,这需要多次传输(以及对结构的内部理解).它类似于尝试使用库哈希函数,然后通过将根指针传递给send函数,在套接字上通过网络发送其内容.

可以编写一些自己的实用程序,在单个内存块中管理一个非常简单的关联数组(或哈希).如果数据量很小,它可以使用简单的线性搜索条目,并且是一个相当紧凑的代码.

Answer 3

试试uthash,一个在C中实现哈希表的头库.它很小,而且相当容易使用.

Answer 4

这是一个旧线程，但我认为这对于寻找实现的任何人来说仍然有用。不需要太多代码；我在没有任何额外库的情况下用了约 100 行代码完成了我的工作。我称它为字典，因为它（某种程度上）与 python 数据类型相似。这是我的代码：

#include <stdlib.h>
#include <stdio.h>
#include <stdbool.h>

typedef struct hollow_list hollow_list;

struct hollow_list{
    unsigned int size;
    void *value;
    bool *written;
    hollow_list *children;
};

//Creates a hollow list and allocates all of the needed memory
hollow_list hollow_list_create(unsigned int size){
    hollow_list output;
    output = (hollow_list) {.size = size, .value = (void *) 0, .written = calloc(size, sizeof(bool)), .children = calloc(size, sizeof(hollow_list))};
    return output;
}

//Frees all memory of associated with a hollow list and its children
void hollow_list_free(hollow_list *l, bool free_values){
    int i;
    for(i = 0; i < l->size; i++){
        hollow_list_free(l->children + i, free_values);
    }
    if(free_values){
        free(l->value);
    }
    free(l);
}

//Reads from the hollow list and returns a pointer to the item's data
void *hollow_list_read(hollow_list *l, unsigned int index){
    if(index == 0){
        return l->value;
    }
    unsigned int bit_checker;
    bit_checker = 1<<(l->size - 1);
    int i;
    for(i = 0; i < l->size; i++){
        if(bit_checker & index){
            if(l->written[i] == true){
                return hollow_list_read(l->children + i, bit_checker ^ index);
            } else {
                return (void *) 0;
            }
        }
        bit_checker >>= 1;
    }
}

//Writes to the hollow list, allocating memory only as it needs
void hollow_list_write(hollow_list *l, unsigned int index, void *value){
    if(index == 0){
        l->value = value;
    } else {
        unsigned int bit_checker;
        bit_checker = 1<<(l->size - 1);
        int i;
        for(i = 0; i < l->size; i++){
            if(bit_checker & index){
                if(!l->written[i]){
                    l->children[i] = hollow_list_create(l->size - i - 1);
                    l->written[i] = true;
                }
                hollow_list_write(l->children + i, bit_checker ^ index, value);
                break;
            }
            bit_checker >>= 1;
        }
    }
}

typedef struct dictionary dictionary;

struct dictionary{
    void *value;
    hollow_list *child;
};

dictionary dictionary_create(){
    dictionary output;
    output.child = malloc(sizeof(hollow_list));
    *output.child = hollow_list_create(8);
    output.value = (void *) 0;
    return output;
}

void dictionary_write(dictionary *dict, char *index, unsigned int strlen, void *value){
    void *hollow_list_value;
    dictionary *new_dict;
    int i;
    for(i = 0; i < strlen; i++){
        hollow_list_value = hollow_list_read(dict->child, (int) index[i]);
        if(hollow_list_value == (void *) 0){
            new_dict = malloc(sizeof(dictionary));
            *new_dict = dictionary_create();
            hollow_list_write(dict->child, (int) index[i], new_dict);
            dict = new_dict;
        } else {
            dict = (dictionary *) hollow_list_value;
        }
    }
    dict->value = value;
}

void *dictionary_read(dictionary *dict, char *index, unsigned int strlen){
    void *hollow_list_value;
    dictionary *new_dict;
    int i;
    for(i = 0; i < strlen; i++){
        hollow_list_value = hollow_list_read(dict->child, (int) index[i]);
        if(hollow_list_value == (void *) 0){
            return hollow_list_value;
        } else {
            dict = (dictionary *) hollow_list_value;
        }
    }
    return dict->value;
}

int main(){
    char index0[] = "hello, this is a test";
    char index1[] = "hello, this is also a test";
    char index2[] = "hello world";
    char index3[] = "hi there!";
    char index4[] = "this is something";
    char index5[] = "hi there";

    int item0 = 0;
    int item1 = 1;
    int item2 = 2;
    int item3 = 3;
    int item4 = 4;

    dictionary d;
    d = dictionary_create();
    dictionary_write(&d, index0, 21, &item0);
    dictionary_write(&d, index1, 26, &item1);
    dictionary_write(&d, index2, 11, &item2);
    dictionary_write(&d, index3, 13, &item3);
    dictionary_write(&d, index4, 17, &item4);

    printf("%d\n", *((int *) dictionary_read(&d, index0, 21)));
    printf("%d\n", *((int *) dictionary_read(&d, index1, 26)));
    printf("%d\n", *((int *) dictionary_read(&d, index2, 11)));
    printf("%d\n", *((int *) dictionary_read(&d, index3, 13)));
    printf("%d\n", *((int *) dictionary_read(&d, index4, 17)));
    printf("%d\n", ((int) dictionary_read(&d, index5, 8)));
}

不幸的是，您无法复制 list[x] 语法，但这是我想出的最佳替代方案。