Which one is better std::prev(itr) or --itr?

Question

I am iterating through a bidirectional data structure. I can do it either by using (++ , --) or (std::prev,std::next,std::advance). Is there a advantage of using later over the other?

Answer 1

They slightly do different things. So neither is better in general.

In particular std::prev doesn't modify itr. So, it is better when itr shouldn't or couldn't (see S.M.'s answer for example of latter) be modified. --itr and std::advance do modify itr, so they are better when itr must be modified.

An advantage of std::prev and std::advance over --itr is their argument n which allows avoiding writing a loop when you need to advance multiple steps. They're more efficient than a loop if the iterator is random access.