Memory allocating array of structure pointers in c

Question

I'd like to pass an array of pointers of structure addresses which has varying size and access structure members. But by passing the array of structure objects the data is irregular and library functions are giving SIGABRT signal. This is a part of my code-

struct data *device_info;

device_info = malloc(device_count*sizeof(void );
ipbt_database_manager_get_device_info(device_info, "all", device_count);

This is the function definition-

bool ipbt_database_manager_get_device_info(struct data *dev_info_ptr, char *device_id, int device_count)
{
    struct node *current_device_info = first_device_info;
    int count = 0;

    if (!strcmp(device_id,"all")) {
        while (current_device_info != NULL) {
            dev_info_ptr[count] = current_device_info->node_data;
            count++;
            current_device_info = current_device_info->next;
        }
}

I'm curious. What do you think sizeof(void) is supposed to give you? — StoryTeller - Unslander Monica
– StoryTeller - Unslander Monica, Commented Feb 16, 2017 at 13:27
It gives enough space to store address of structure right? size of void is 4 bytes. — Govindh
– Govindh, Commented Feb 16, 2017 at 13:29
node struct id declared and malloc' ed in a different c file. It is an existing database ie a linked list. — Govindh
– Govindh, Commented Feb 16, 2017 at 13:31

StoryTeller - Unslander Monica · Accepted Answer · 2017-02-16 14:20:58Z

4

Your function expects a pointer to a structure, (possibly one of many the lie in consecutive memory).

This should allocate enough memory, which is the memory for a single struct data times device_count:

struct data *device_info = malloc(sizeof(*device_info) * device_count);
ipbt_database_manager_get_device_info(device_info, "all", device_count);

I omitted that check for NULL (which you must preform), and I united the pointer definition with its initialization.

edited Feb 16, 2017 at 14:20

answered Feb 16, 2017 at 13:30

StoryTeller - Unslander Monica

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7 Comments

Govindh Over a year ago

Does it copy the data to newly allocated memory or just copy the address of the original database(structure)?

StoryTeller - Unslander Monica Over a year ago

@Govindh - It passes a consecutive buffer to ipbt_database_manager_get_device_info.

Govindh Over a year ago

I just need to save the starting addresses of the structure database,not the whole thing. Is there any way to do that.

chux Over a year ago

@StoryTeller Curious, any particular reason for malloc(count * sizeof *ptr) vs. malloc(sizeof *ptr * count)? I find the 2nd form better when malloc(sizeof *ptr * row * col) insures at least size_t math throughout the product calculation.

StoryTeller - Unslander Monica Over a year ago

@chux - personal style preference. I just find the second form odd to read when the asterisk serves different purposes. Operator precedence while correct doesn't feel "natural" to me.

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