Question

In my code I have a vector of pointers to objects of SomeClass and a (custom comparison) vector-based priority queue that contains pointers to objects of SomeClass:

std::vector<SomeClass*> my_vector;
std::priority_queue<SomeClass*, vector<SomeClass*>, CustomCompare> my_queue;

Initially my_vector is empty and my_queue is full. Gradually my_queue is emptied into my_vector like this:

my_vector.push_back(my_queue.top());
my_queue.pop();

My question is: Will my_queue.pop() delete the memory that was allocated to the SomeClass object that was pushed back to my_vector therefore causing the element of my_vector to be a dangling pointer? Or otherwise, does the vector make a deep or a shallow copy of the object pointed to by the pointer returned by my_queue.top()?

Answer 1

No deletions will be made. The only thing being copied/removed/pushed_back are pointers. The objects these point to remain alive, provided they have been dynamically allocated. In that case, you will have to do the clean-up yourself.

Depending on the behaviour desired, you may want to use smart poitners to avoid manual memory management, store SomeClass objects instead of pointers, or leave things as they are and make sure to make a cleanup at the end. Bear in mind that it can be difficult to guarantee that your program will safely get to the point where the memory is released, which is one reason smart pointers are preferred over raw pointers to dynamically allocated objects.