Structs and Segmentation Faults.

#include <stdlib.h>
#include <stdio.h>
#include <pthread.h>
#include "threadpool.h"

//forward declarations
struct thread_pool;
struct future;
struct future *list_create(int val);
void *thread_helper(void *arg);

//stores list of futures
struct thread_pool {
	struct future *list;
};

//stores pointer to method call
struct future { 
	thread_pool_callable_func_t data;
	int val;
	struct future *next;
};

//create a list
struct future *list_create(int val) {
	struct future *node;
	if(!(node=malloc(sizeof(struct future)))) return NULL;
	node->val=val;
	node->next=NULL;
	node->data=NULL;

	return node;	
}

int main() {
	struct thread_pool *threadpool;

        /* segmentation fault occurs at threadpool->list assignment */
	threadpool->list = list_create(1);

	return 0;
}