(1) I am curious about a certain aspect of how the g++ optimizer works at -O3. If I have a for-loop, there are times when it is beneficial to have a function call in the while-condition. For instance: vector<int> v; ... for ( int i=1; i < v.size(); ++i) Now, I if v is not changing inside of that for-loop, then this would appear at first glance to be more efficient: int max = v.size(); for ( int i=1; i < max; ++i) By using 'max' instead of v.size(), I am eliminating a function call from every iteration of the for loop. If the loop is iterated a large number of times, this could have an advantage. However, is it all the same when you are optimizing? Does g++ remove the need for the second method? Before I end this email, I am sure that at least someone is thinking, "Wait, you're using a vector, and using an old style for loop to traverse it instead of iterators!" Well, yes, that's true. But I'm doing that for two reasons -- 1) I'm interested in the question as it stands, so I asked it the way I did, and 2) My next question will already cover that, as it involves a comparison between traversing an array as I do above and using iterators. (2) Is there a big difference in speed between using a standard for-loop for vector traversal and using iterators? I already verified that I can get a significant speed improvement (with very large N) by accessing the vector directory with v[i] instead of using the at() method. But what about iterators? If I write it with iterators instead, will that be optimized out at -O3 to reduce to essentially the same thing?
