How to access the 'previous' element in a C++ list iterator loop?

Question

I'm trying to access the previously iterated element in a loop going through all the elements of a list.

To be more specific, my loop looks like this:

for (iter=list_object.begin(); iter!= list_object_.end(); iter++)
  {
    function_1(*iter);
    function_2(*PREVIOUS_VALUE_IN_THE_LIST);
  }

How do I access this previous value in the list?

Answer 1

An easy way is to simply keep track of the previous element in the for loop, such as:

for( list_t::iterator iter=obj.begin(), prev=obj.end(); 
    iter != obj.end(); prev=iter, ++iter )
{
  function_1(*iter);
  if( prev != obj.end() )
    function_2(*prev)
}

This will work with iterators which are simply Forward, they don't need to be Bidirectional.