vector::at vs. vector::operator[]

Question

I know that at() is slower than [] because of its boundary checking, which is also discussed in similar questions like C++ Vector at/[] operator sp

Answer 1

Note: It appears some new folks are downvoting this answer without having courtesy of telling what is wrong. Below answer is correct and can be verified here.

There is really only one difference: at does bounds checking while operator[] doesn’t. This applies to debug builds as well as release builds and this is very well specified by the standards. It’s that simple.

This makes at a slower method but it’s also really bad advice to not to use at. You have to look at absolute numbers, not relative numbers. I can safely bet that most of your code is doing fat more expensive operations than at. Personally, I try to use at because I don’t want a nasty bug to create undefined behavior and sneak in to production.