Problem to get a list of list in C++ predicate

I have a problem with a C predicate I've written. I have a list of
list in input ([[1,2,3],[4,5,6]]). And I would like to put that in a
short **. I don't know how I can do that.

I have these lines in my fonction :
/*************************************************************************/
i=0;
for(ecword_list = ecword_liste_trou ; ecword_list.is_list(car,cdr) ==
EC_succeed; ecword_list = cdr)//walk through the main list
{//construction of the list but I'm not sure, I think the problem is here
	list_tmp = list(car,cdr); 
	nb = liste_taille_domaine[i]; //get the length of the list
	if(nb>0)
	{
		liste_trou[i] = (short *)malloc(nb*sizeof(short)); // allocation of memory
		j=0;
		for(ecword_list2 = list_tmp ; ecword_list2.is_list(car2,cdr2) ==
EC_succeed; ecword_list2 = cdr2)//walk through the little list
		{
			res = car2.is_long(&x);//recuperation of the element
			if (res != EC_succeed) return res;
			liste_trou[i][j]=x;//I put element in my short **
			j++;
		}
	}
	i++;
}
/*************************************************************************/

The problem is when I would like to build the list which in the other list.