std::vector::reserve and reducing memory reallocations

[Carmelo908]

Channel

C++Weekly

Topics

It's said that you shouldn't add elements to a std::vector while iterating it, because it may cause a reallocation and this will cause all iterators to be left dangling. But what if we use std::vector::reserve before creating those iterators to avoid reallocation? what is the frequency with which std::vector has to reallocate itself when adding new elements? If I know my final size before hand, how much of a performance difference will make to call vector::reserve before my operations?

Length

I don't think this would take more than 10 minutes to explain

[LB--]

There's not much to explain, the standard guarantees that no reallocations will occur if you stay within the reserve size you requested, so if you reserve the final size in advance there will be no reallocations and no iterator invalidations.

[Carmelo908]

Well, I find it very strange that I don't see anyone talking about reserve (which is also in std::string by the way)