hcc_nextitem
while ((item = hcc_nextitem(trans, head, item)) == NULL) {
struct HCLeaf *hcc_nextitem(hctransaction_t trans, struct HCHead *head, struct HCLeaf *item);
#define hcc_firstitem(trans, head) hcc_nextitem(trans, head, NULL)
item = hcc_nextitem(trans, head, item))