vector iterator not incrementable, which is related to the operation of iterator and erase

Question

I am searching for a long time on net. But no use. Please help or try to give some ideas how to solve this problem.

class Solution{
public:
    int removeElement(vector<int> &nums, int val)
    {

        for (auto &it = nums.begin(); it != nums.end(); ++it)
        {
            if (*it == val)
            {
                it = nums.erase(it);
            }
        }
        return nums.size();
    }
};
int main(void)
{
    Solution s; 
    vector<int> vi = { 3, 2, 2, 3 };
    cout << "size = " << s.removeElement(vi, 3) << endl;
    for (auto &i : vi)
    {
        cout << i << " ";
    }
    cout << endl;

    return 0;
}

which are the class body and main function body of my code. But when i run it, compiler popped a window:

enter image description here

That's not the compiler showing an error, that is your program *crashing*. — Some programmer dude, May 15 '16 at 07:48
By the way: http://stackoverflow.com/a/347478/440119 -- It's not only convenient, it's more runtime efficient than your method. — Benjamin Lindley, May 15 '16 at 08:06
@BenjaminLindley Thanks for your guide. Those answers of that question wide my mind — Bowen Peng, May 15 '16 at 08:14

score 2 · Accepted Answer · answered May 15 '16 at 07:48

After erasing the last element, it becomes nums.end() and incrementing it is not allowed.

You shouldn't increment it after erasing. This will also fix problem that one element is skipped after erasure.

Also the & in auto &it = nums.begin() should be removed because having it will make it invalid initialization of non-const reference.

Try this:

#include <iostream>
#include <vector>

using std::vector;
using std::cout;
using std::endl;

class Solution{
public:
    int removeElement(vector<int> &nums, int val)
    {

        for (auto it = nums.begin(); it != nums.end();)
        {
            if (*it == val)
            {
                it = nums.erase(it);
            } else
            {
                ++it;
            }
        }
        return nums.size();
    }
};
int main(void)
{
    Solution s; 
    vector<int> vi = { 3, 2, 3, 3, 2, 3 }; // added testcase of consecutive 3
    cout << "size = " << s.removeElement(vi, 3) << endl;
    for (auto &i : vi)
    {
        cout << i << " ";
    }
    cout << endl;

    return 0;
}

Thanks for your help, Now I understand the reason why my program crashed. — Bowen Peng, May 15 '16 at 07:51

vector iterator not incrementable, which is related to the operation of iterator and erase

1 Answers1