Removing item from vector while iterating?

Question

I have a vector that holds items that are either active or inactive. I want the size of this vector to stay small for performance issues, so I want items that have been mark

Answer 1

You might want to consider using a std::list instead of a std::vector for your data structure. It is safer (less bug prone) to use when combining erasure with iteration.

Answer 2

Removing items from the middle of a vector will invalidate all iterators to that vector, so you cannot do this (update: without resorting to Wilx's suggestion).

Also, if you're worried about performance, erasing items from the middle of a vector is a bad idea anyway. Perhaps you want to use an std::list?

Answer 3

As they said, vector's iterators get invalidated on vector::erase() no matter which form of iterator increment you use. Use an integer index instead.

Answer 4

I agree with wilx's answer. Here is an implementation:

// curFiles is: vector < string > curFiles;

vector< string >::iterator it = curFiles.begin();

while(it != curFiles.end()) {

    if(aConditionIsMet) {

        it = curFiles.erase(it);
    }
    else ++it;
}

Answer 5

You can do that but you will have to reshuffle your while() a bit, I think. The erase() function returns an iterator to the element next after the erased one: iterator erase(iterator position);. Quoting from the standard from 23.1.1/7:

The iterator returned from a.erase(q) points to the element immediately following q prior to the element being erased. If no such element exists, a.end() is returned.

Though maybe you should be using the Erase-remove idiom instead.

Answer 6

If someone need working on indexes

vector<int> vector;
for(int i=0;i<10;++i)vector.push_back(i);

int size = vector.size();
for (int i = 0; i < size; ++i)
{
    assert(i > -1 && i < (int)vector.size());
    if(vector[i] % 3 == 0)
    {
        printf("Removing %d, %d\n",vector[i],i);
        vector.erase(vector.begin() + i);
    }

    if (size != (int)vector.size())
    {
        --i;
        size = vector.size();
        printf("Go back %d\n",size);
    }
}