1.2.1.6 Erasure

• So, in short: generally speaking, you should not delete the items from the list while iterating through it, because the deletion may invalidate the iterator (and the program will possibly crash). If you are however completely sure that the items which you delete are not the values referenced by any of the iterators which you use at the moment of deletion, you may delete.
• Beware that for the other STL containers (e.g. vectors) the constraint is even more strict: deleting from the container invalidates not only iterators pointing to the deleted item, but possibly other iterators, too! So deleting from that containers while iterating through them is even more problematic.
• Choose carefully among erasing options: To eliminate all objects in a container that have a particular value.
  1. For vector, string or deque, use erase-remove. Don’t use for loop, it will invalid the iterator.
  2. For a list, use it’s own remove or remove_if.
  3. For associative container, use its erase member function.
  vect.erase(remove(vect.begin(), vect.end(),1963), vect.end()); 
  list.remove(1963); 
  map.erase(1963);
• To eliminate all objects in a container that satisfy a particular predicate, 1)for vector, string or deque, use erase-remove. 2) for a list, use remove_if, 3) for associative container, write loop being sure to postincrement your iterator. detail can be sen in effective STL item 9;
  bool badValue(int x); 
  vc.erase(remove(vc.begin(), vc.end(), badValue), 
                                            vc.end()); 
   
  lsit.remove_if(badValue); 
  for(auto i = map.begin();i!=map.end(); /* no ++i here*/) { 
          if(badVaue(*i)) map.erase(i++); 
          // or i = map.erase(i); 
          else  ++i; 
  }
• To do something inside the loop (in addition to erasing objects); You can’t use remove, just write a loop,
  bool badValue(int x); 
  for(vect<int>::iterator i = vect.begin();i!=vect.end(); ){ 
          if(badVaue(*i)) { 
                  i = vect.erase(i); 
                  ...do something else 
          } 
          else  ++i; 
  }