Question

I want to loop through a vector and erase certain elements that correspond to a certain criteria, for example:

vector<int> myvector;
vector<int>::iterator it;

myvector.push_back(1);
myvector.push_back(2);
myvector.push_back(3);
myvector.push_back(4);

for(it = myvector.begin(); it != myvector.end(); ++it){

    if((*it) == 4){
        it = myvector.erase(it);
    }
}

Now this works fine unless the criterion erases the last item like in the code above. How do you avoid this behaviour ?

Thanks.

EDIT————————————

Now the reason I was looping through it was that there are actually 4 vectors I need to delete the element from (but the criterion is only on one vector):

In this case, is this how to go ?

vector<int> myvector;
vector<int> myvector2;
vector<int> myvector3;
vector<int> myvector4;
vector<int>::iterator it;
vector<int>::iterator it2;
vector<int>::iterator it3;
vector<int>::iterator it4;

myvector.push_back(1);
myvector.push_back(2);
myvector.push_back(3);
myvector.push_back(4);

(assume myvector2/3/4 have values inside them)

it2 = myvector2.begin()
it3 = myvector3.begin()
it4 = myvector4.begin()

for(it = myvector.begin(); it != myvector.end();){

    if((*it) == 4){
        it = myvector.erase(it);
        it2 = myvector2.erase(it2);
        it3 = myvector3.erase(it3);
        it4 = myvector4.erase(it4);
    }
    else{
    ++it;
    ++it2;
    ++it3;
    ++it4;
    }
}

Is there a modification to the erase/remove idiom valid in this case ?

Answer 1

Don’t do this with a for loop, there’s already a well-debugged algorithm for you.

myvector.erase(std::remove(myvector.begin(), myvector.end(), 4), myvector.end());