C - Linked List and pointer problem
-
28-09-2019 - |
문제
Hey,
I'm a beginner in C and tried to implement my own linked list implementation, that basically looks like this:
struct Element
{
void *value;
struct Element *next;
};
typedef struct
{
struct Element *first;
struct Element *last;
unsigned int size;
} LinkedList;
void LinkedList_init(LinkedList *this)
{
this->size = 0;
this->first = NULL;
this->last = NULL;
}
void LinkedList_add(LinkedList *this, void *value)
{
struct Element *node = malloc(sizeof(struct Element));
node->value = value;
node->next = NULL;
if (this->size == 0)
this->first = this->last = node;
else
{
this->last->next = node;
this->last = node;
}
this->size++;
}
So in short, I want a linked list that can hold arbitrary types - I heard, this is possible in C by using void pointers. The problem now arises, when I want to use that implementation, for example with a structure as value:
typedef struct
{
int baz;
} Foo;
int main(void)
{
LinkedList list;
Foo bar;
bar.baz = 10;
LinkedList_init(&list);
LinkedList_add(&list, (void *) &bar);
/* try to get the element, that was just added ... */
Foo *firstElement = (Foo *)list.first;
/* ... and print its baz value */
printf("%d\n", firstElement->baz);
return 0;
}
The last printf call just prints values like -1077927056, which look like a memory address. So it's probably a problem with pointers. After searching the web the last few days for a similar issue on the web (I had no luck with that), I tried to throw my own logic away and tested various random *& combinations. Turns out, that was a dead end, too. :(
It's probably something simple for a more experienced C programmer, but I just can't find the answer. Please help :D
해결책
list.fist
is a struct Element
.
Try:
Foo *firstElement = (Foo *)(list.first->value);