Delete elements in a vector using a list of iterators?

Question

Lets suppose I have a unsorted list of iterators to delete defined as

std::vector<std::vector<int>::iterator>  _unsortedIterList;

Of another vector defined as:

std::vector<int> _listValues;

Then this code will not work (since erasing will invalidate the remaining iterators).

for ( auto it: _unsortedIterList)
{
   _listValues.erase(it);
}

Is there a way to erase all of the iterators properly?

Barry · Accepted Answer · 2017-12-14 18:16:38Z

4

Erasing invalidates iterators at or after the point of erase. So all you have to do is ensure that we erase back to front:

// because random access iterators are comparable
std::sort(_unsortedIterList.begin(), _unsortedIterList.end(),
    std::greater<>{});

// now this is back-to-front, so each erase will keep every other iterator valid
for (auto it : _unsortedIterList) {
    _listValues.erase(it);
}

answered Dec 14, 2017 at 18:16

Barry

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