Question

when and how are iterators invalidated in a map when using the erase method ?

for example :

std :: map < int , int > aMap ;

aMap [ 33 ] = 1 ;
aMap [ 42 ] = 10000 ;
aMap [ 69 ] = 100 ;
aMap [ 666 ] = -1 ;

std :: map < int , int > :: iterator itEnd = aMap.lower_bound ( 50 ) ;

for ( std :: map < int , int > :: iterator it = aMap.begin ( ) ;
      it != itEnd ;
      // no-op
    )
{
   aMap.erase ( it ++ ) ;
}

the erased iterator will surely become invalid (it’s incremented while still valid)
but what about the others?

if I’m not wrong the standard says that a map has to be a balanced binary tree or a structure with equivalent key-search complexity

in case the map is implemented with a tree, can I assume that not erased iterators remain valid ?

what about other possible ways to implement a map ?

Answer 1

Only the erased iterator is invalid, the rest are guaranteed by the standard to remain valid.

See Iterator invalidation rules