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c++for-looppush-backstdlistfor-range

inserting into the back of std::list during range based for loop

I came across "Add elements to a vector during range-based loop c++11", and wasn't surprised it's not allowed using std::vector because the append can invalidate iterators. However, inserting into std::list doesn't invalidate any of the iterators, so I was wondering if it would be allowed with std::list instead of std::vector.

e.g.

std::list<int> list({1});
for (int &cur : list)
{
    std::cout << cur << " ";
    if (cur < 10)
    {
        list.push_back(cur + 1);
    }
}

It seems to compile fine, but I'm worried it's undefined behaviour.

Solution

  • Yes, inserting / removing elements of a std::list does not invalidate pointers, references, or iterators to elements, except for the removed element. Not even the end-iterator is changed or invalidated.

    Thus, it is safe.

    But as one has to carefully ponder about safety, it is still inadvisable.