Speed accessing a std::vector by iterator vs by operator[]/index?

Question

Say, I have a

std::vector v;

in my code and I need to access its elements very often in the program, looping them forwa

Answer 1

I'd go for iterators, but what I would optimize is calling end() in the loop and would change preincrement to postincrement. I.e. I'd

std::vector v;
std::vector::iterator i,ie;
std::vector::reverse_iterator j,je;

// i loops forward, j loops backward
for( i=v.begin(),ie=v.end(), j=v.rbegin(),je=v.rend(); i!=ie && j!=je; ++i,++j ){
    // some operations on v items
}

And I don't think it's premature microoptimization, it's just writing better code. Much less evil than calling every attempt to write efficient code premature microoptimization and substituting thinking with profiling.