Question

I am writing an email application that interfaces with a MySQL database. I have two tables that are sourcing my data, one of which contains unsubscriptions, the other of which is a standard user table. As of now, I’m creating a vector of pointers to email objects, and storing all of the unsubscribed emails in it, initially. I then have a standard SQL loop in which I’m checking to see if the email is not in the unsubscribe vector, then adding it to the global send email vector. My question, is, is there a more efficient way of doing this? I have to search the unsub vector for every single email in my system, up to 50K different ones. Is there a better structure for searching? And, a better structure for maintaining a unique collection of values? Perhaps one that would simply discard the value if it already contains it?

Answer 1

If your C++ Standard Library implementation supports it, consider using a std::unordered_set or a std::hash_set.

You can also use std::set, though its overhead might be higher (it depends on the cost of generating a hash for the object versus the cost of comparing two of the objects several times).

If you do use a node based container like set or unordered_set, you also get the advantage that removal of elements is relatively cheap compared to removal from a vector.