How to iterate over a vector?

Question

I need to iterate over a vector strictly in the order the elements were pushed back into it. For my particular case it's better use iterators than iterating though the for-each loop as follows:

std::vector<int> vector;
for(int i = 0; i < vector.size(); i++)
   //not good, but works

My question is if it's realiably to iterate over the vector through iterator like that:

std::vector<int> v;
for(typename std::vector<int>::iterator i = v.iterator(); i != v.end(); i++)
   //good, but I'm not strictly sure about the iterating order.

So, can I use iterators safely with my requirements? Is it standartized?

Answer 1

If you have access to C++11 you can use range-based for loops

for (auto i : v)

Otherwise you should use begin() and end()

for (std::vector<int>::iterator i = v.begin(); i != v.end(); ++i)

You can also use std::begin and std::end (these require C++11 as well)

for (std::vector<int>::iterator i = std::begin(v); i != std::end(v); ++i)

begin will return an iterator to the first element in your vector. end will return an iterator to one element past the end of your vector. So the order in which you get the elements iterating this way is both safe and defined.

Answer 2

if you want to use iterators, your approach is fine

for(auto it = v.begin(); it != v.end(); ++it)

the iteration order depends in fact on the container and the actual used iterator. for a std::vector this code iterates always over the elements in their order in the vector. if you'd use v.rbegin() or v.rend() instead, the order would be reversed. for another container the order is different, for a std::set the very same code would iterate the elements in ascending order of their sorting criterion.