fwd_cmp
fwd->tree = rbtree_create(fwd_cmp);
int fwd_cmp(const void* k1, const void* k2);
else if(fptr == &fwd_cmp) return 1;
fwd->tree = rbtree_create(fwd_cmp);
int fwd_cmp(const void* k1, const void* k2);
else if(fptr == &fwd_cmp) return 1;