Re: Using std::set::erase with iterators

From:
Ondra Holub <ondra.holub@post.cz>
Newsgroups:
comp.lang.c++
Date:
Mon, 3 Mar 2008 02:20:58 -0800 (PST)
Message-ID:
<f4854fd6-e6de-49cc-89f8-a807dc5ec02b@q78g2000hsh.googlegroups.com>
On 3 B=F8e, 10:43, mathieu <mathieu.malate...@gmail.com> wrote:

Hi,

  I do not understand how I am supposed to use erase when looping over
elements in a set, here is what I am trying to do (*). Could someone
please indicate how was I supposed to do it properly ? All I can think
of is something like this (very cumbersome):

    if( *it % 2 )
      {
      std::set<int>::const_iterator duplicate = it;
      ++it;
      s.erase( duplicate );
      }
    else
      {
      ++it;
      }

Thanks
-Mathieu

(*)
#include <set>
#include <iostream>

int main()
{
  std::set<int> s;
  for(int i =0; i < 10; ++i)
    {
    s.insert( i );
    }

  for( std::set<int>::const_iterator it = s.begin(); it != s.end(); +
+it)
    {
    if( *it % 2 )
      s.erase( it );
    }

  for( std::set<int>::const_iterator it = s.begin(); it != s.end(); +
+it)
    {
    std::cout << *it << std::endl;
    }

  return 0;

}


If you erase some item, iterators become invalid. So you cannot
continue with the cycle driven by invalid iterators.

Use std::remove_if and std::set::erase(std::remove_if(begin, end,
condition), end) instead. (begin and end are range limits in your set)

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