Re: Problems removing an element from a std::set using a reverse_iterator

Carl Barron <>
Wed, 25 Jul 2007 18:51:28 CST
In article <>,
irotas <> wrote:

However, if it's really
true that there's no good way to remove elements from a container
while iterating over it in reverse, that seems to be a severe language

  Just use iterators and decrement operations as appropriate:
  UIntSet::iterator it(uis.end());
   while(it !=uis.begin() && pred(*--it)) uis.erase(it++);

note there is no dereference of iterators pointing to erased items.
and no gyrations needed using reverse_iterator.
 // easiest way to get the SFINAE class that tests for
// typedef ... key_type;
#include <boost/mpl/has_xxx.hpp>

template <class C,class B=has_key_type<C>::type>
struct erase_struct
   typedef typename C::iterator iterator;
   static iterator exec(C &c,iterator it)
      // emulate recent drafts
      return it;

template <class C>
struct erase_struct<C,boost::mpl::false_>
   typedef typename C::iterator iterator;
   static iterator exec(C &c,iterator it)
      return c.erase(it);

template <class C,class Pred>
void erase_backward_if(C &c,Pred pred)
   typename C::iterator it(c.end());
   while( it != c.begin() && pred(*--it))

looks generic. but not tested.
note no dereferencing of invalid iterators in all cases.

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