Pointer to std::vector

Question

So here is the problem I am having.

I have a pointer to std::vector. So after I initialize the pointer, I don't add any items to the vector, nor remove any. However, at a certain point in my code, my std::vector moves locations, and I end up with a dangling pointer. This seems to happen randomly, even though I never touch the vector after making the pointer

It took me a while debugging this, to figure this problem out. Is there a way to guarantee that my std::vector will not change memory locations? Or is it just a bad idea to have a pointer to a vector.

Answer 1

Or is it just a bad idea to have a pointer to a vector?

In general, I would say it is a bad idea to have raw pointers for controlling an object's lifetime. Don't use raw pointers and automatic memory management, try using smart pointers with the appropriate ownership semantics ( std::shared_ptr<> or std::unique_ptr<> ). Use raw pointers only for observing pointers (and if you want to be able to verify at run-time whether they are dangling, use weak_ptr<> ).

Also, in many cases you may realize you do not need a pointer at all. In that case, just use an object with automatic storage, which can be efficiently moved around or passed/returned by value in C++11 thanks to move semantics.

Answer 2

This seems to happen randomly

No, it doesn't. As long as it stays in scope it has the same address. What is probably happening is that the vector is going out of scope, and since it was automatically allocated (sounds like) it is getting destroyed at that time. What you can do is allocate the vector on the heap (for eg int s):

std::vector<int>* pv = new std::vector<int>();

Then you will not have this problem. However you must remember to explicitly delete it with

delete vp;

before pv goes out of scope or you'll get a memory leak.