Use pointers to items in a vector, and deleting items from the vector

Question

I have std::vector of some class, and in my program I have some pointers to several items in the vector, the problem is when I delete one item, for example the first item, all pointers are wrong, this is an example of code:

vector<int> numbers;
numbers.push_back(100);
numbers.push_back(200);
numbers.push_back(300);

int *pNum = & numbers[1]; // pNum pointer to 200

numbers.erase(numbers.begin()); // now pNum pointer to 300

I understand why it happens, the question is whether there is a way to solve the problem?

Answer 1

You could use a node-based structure, such as an std::list . This guarantees that iterators other than those to erased elements remain valid.

The drawbacks are that you have no random access, and that the data aren't contiguous.

Answer 2

You can save pointers in the vector. This way, you separate the data from the vector, and your reference points to the real data.

vector<int*> numbers;

numbers.push_back(new int(100));
numbers.push_back(new int(200));
numbers.push_back(new int(300));

int * pNum  = numbers[1];

// memory leak!!!
numbers.erase( numbers.begin() );

cout << *pNum << endl;

It's safe, if you use c++11, to put shared_ptr s instead of raw pointers.