Finding NULL pointers in std vectors

Question

I'm working with vectors and at some point there will be NULL entries; I want to erase all NULL occurrences within the given vectors. My approach so far is not working:

for(int i = sent_flit_list->size() - 1; i >= 0; i--)
if(sent_flit_list[i] == NULL)
    sent_flit_list->erase(sent_flit_list[i]);

for(int i = sent_pkt_list->size() - 1; i >= 0; i--)
if(sent_pkt_list[i] == NULL)
    sent_pkt_list->erase(sent_pkt_list[i]);

Where

vector<Flit*> *sent_flit_list;
vector<Packet*> *sent_pkt_list;

are the vectors. I have tried casting to a type (Flit*)NULL/(Flit*)0 but with no success.

Any help will be greatly appreciated.

Answer 1

Use the Erase-Remove idiom to remove elements based on a predicate from a container.

In your case:

// with a predicate
my_vec.erase(std::remove_if(begin(my_vec), end(my_vec), 
                           [](Flit* x) { return x == nullptr; }), 
             end(my_vec));

// with a value value
my_vec.erase(std::remove(begin(my_vec), end(my_vec), nullptr),
             end(my_vec));

Your current approach isn't working, because vector::erase expects an iterator to an element of the vector and not a value of the stored type.

Frankly, what you are doing seems a little bit strange. You shouldn't store pointers, but values in containers. If you require nullable values, use a Maybe class such as boost::optional.