Re: Erase in a map

From:

"freak" <farid.mehrabi@gmail.com>

Newsgroups:

microsoft.public.vc.stl

Date:

19 Mar 2007 02:43:21 -0700

Message-ID:

<1174297401.488107.309760@b75g2000hsg.googlegroups.com>

On Mar 16, 9:35 pm, Charles Zhang <CharlesZh...@newsgroups.nospam>
wrote:

I want to erase items in a map based on some criteria. However, as soon
as the erase is called, iterator become invalid. I would like someone
to tell me the better way to do it.

Here is the source code I am using, and it is crashing.

   for ( pos = connectionMap.begin(); pos != connectionMap.end(); ++pos){
         ConnectionInfo* conn = pos->second;

         if ( current - conn->lastRequestTime > 60 * timeOut ) {
           connectionMap.erase(pos);
         }
    }

To overcome the problem, I start the loop from the beginning after a
item is removed. But this is too slow.

Thanks

Charles Zhang

use standard library:
#include <algorithm>

/*assuming that TConnectionMap implements std::map<long,ConnectionInfo
*> */

typedef std::map<long,ConnectionInfo *> TConnectionMap;

struct ConnExpired{//define a predicate class;

     ConnExpired(const long cur): current(cur) {};

     bool operator () (const TConnectionMap::value_type& conn)
const
     {
           return current - conn.second->lastRequestTime > 60 *
timeOut ;
     };

private:
    const long current;
};

{//somewhere in the code:
     TConnectionMap connectionMap;
     long current;
     std::remove_if
(connectionMap.begin(),connectionMap.end(),ConnExpired(current));
};

and do not worry about the validity of the iterators because the
STL(standard template library) is responsible for it.