C++ : deleting multiple elements of a list while iterating the list

c++, erase, iterator, list

Solution

In general, the way to remove elements from a list based depending on a condition is to use the `std::list::remove_if` member function.

bool pred(const Treenode* t) { .... }
currentNewLevel.remove_if(pred);

The predicate can be a functor, so it can keep any state that is required to implement the removal criteria:

#include <algorithm> // for std::find_if
#include <list>

// unary predicate functor. Returns true if an element of a reference
// list satisfies "something" and the functor call argument satisfies "somethingDifferent"
struct Pred
{
  Pred(const std::list<Treenode*>& nodes) : nodes_(nodes) {}
  bool (const Treenode* t) const
  {
    return std::find_if(nodes_.begin(), nodes_.end(), something) != nodes_.end() &&
           somethingDifferent(t);
  }
 private:
  const std::list<Treenode*>& nodes_;
};

then

Pred p(currentLevel);
currentLevel.remove_if(p);

Problem

I know how do erase elements of a list, and that erase return a valid iterater. My problem is, that I want to remove not just one element but multiple. Actuall my code is like ``` for(list<Treenode*>::iterator it=currentLevel->begin(); it!=currentLevel->end(); ++it){ if(something(*it)) { for(list<Treenode*>::iterator it2=currentNewLevel->begin();it2!=currentNewLevel->end();){ if (somethingDifferent(*it2)) { it2=currentLevel->erase(it2); } else { ++it2; } } } } ``` of course this could not work, because `it` is not changed. I don't know how to change the iterator but stay on this iteration-step. Thank you for reading. I hope someone know the answer.

Original source