C++ iterator

I was meaning to understand in C++ what are iterator , I have gone through whats on the web , however still did not get it. could someone please provide explanation , with some example ,
I have always found , seeing an example helps me better than just plain words.

An iterator object is associated to a container so that it points to one element of that container or to an invalid pseudo element which signals the end of the iteration. The iterator provides a function 'next' - mostly via the ++ operator - which makes the iterator object pointing to the next element.

Code:

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// the container
std::vector<int> cont;
cont.push_back(1);
cont.push_back(2);
// the iterator (pointing to nowhere and not yet associated to the container)
std::vector<int>::iterator iter;

for (iter = cont.begin();  // now iter is associated to the container and points to first element
      iter !=cont.end();    // and runs until the iter is end iterator of the container
      ++iter)                    // points to next element after each cycle
{
    int i = *iter;    // get value of element from iterator by dereferencing (it is 1 or 2)
    std::cout << i << std::endl;
}

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thank you , except for the obvious , as looping through the container , what are there practical uses.

Quote:

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Originally Posted by aamir121a

thank you , except for the obvious , as looping through the container , what are there practical uses.

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Well, looping through a container seems to be a very practical use to me, especially for a container such as a std::list or std::map that can't be simply indexed like a vector can.

Due to their ability to make any kind of container "look the same", iterators are also used in almost every STL algorithm such as std::transform() as a generic way to specify data without caring where it's stored.

thanks again much appreciated

Custom iterators can also be useful when you want to iterate from something other than 'first to last'. Many standard containers have a reverse iterator, where incrementing will step backwards through the container. This means that only one algorithm need be written which assumes the availability of a ++ operator in the iterator. It's up to the iterator to define what ++ actually does.