使用memcpy列表中的分段错误

Question

I'm trying to copy a list into another list with memcpy, but I'm getting a segmentation fault everytime I try to access the value I copied.

I've already tried moving pointers around, but the problem still occurs. create_list creates a new head node for the list and returns it. Here is some of the code:

/* The n variable shows the number of elements in the list for the head */
struct list {
    union{
        void *data;
        struct {
            unsigned num;
            List *end;
        };
    };
    List *node;
};
List *
create_list()
{
    List *head;

    head = malloc(sizeof(List));
    if (head == NULL)
        return NULL;
    head->num = 0;
    head->end = NULL;
    head->node = NULL;

    return head;
}
int
cpy_list(List *l1, List **l2)
{
    List *iter;
    void *data_aux;

    *l2 = create_list();
    iter = l1->node;
    while (iter != l1->end) {
        memcpy(&data_aux, iter->data, sizeof(iter->data));
        //printf("data_aux: %s\n", data_aux);
        insert_list(*l2, data_aux, NULL);
        //printf("iter->data: %s\n", iter->data);
        iter = iter->node;
    }

    return 1;
}

void
print_list(List *head)
{
    List *iter;
    iter = head->node;
    printf("[");
    while (iter != head->end) {
        printf("\"%s\",", iter->data);
        iter = iter->node;
    }
    printf("\"%s\"", iter->data);
    printf("]");
    printf("\n");
}

int
main(int argc, char *argv[])
{

    List *l1, *l2;
    char *str[] = {"Test0", "Test1", "Test2", "Test3", "Test4"};
    void *data_aux;
    l1 = create_list();

    for (int k = 0; k < 5; k++) {
        insert_list(l1 ,str[k], NULL);
    }
    printf("l1: ");
    print_list(l1);

    cpy_list(l1, &l2);
    print_list(l2);

    return 0;
}

Answer 1

memcpy(&data_aux, iter->data, sizeof(iter->data));

I'll assume this is a typo problem (let me know if it is not and you intended to use it like that). &data_aux will return the address of variable data_aux , not the address pointed by data_aux . This code is likely causing a stack overflow as you are probably writing data beyond the boundaries of the local variable data_aux (which have the size of a pointer - 4 bytes on x86 or 8 bytes on x64). If iter->data have a significant size you will corrupt the stack and have undefined behavior.

What you probably want is to allocate a buffer to be pointed by data_aux . Something like:

data_aux = malloc(sizeof(iter->data));

And then pass data_aux instead of &data_aux in your call to memcpy .