How to (re)move from a container if predicate is satisfied?

Question

How can I move the element into aux_list using STL algorithm module?

std::remove_copy_if( list.begin( ), list.end( ), std::back_inserter( aux_list ),
                     []( const value_type& item_ptr )
                     {
                         return !item_ptr->is_valid( );
                     } );

So instead of copying from `list` to `aux_list` you want to move the elements? — NathanOliver, Nov 18 '16 at 14:43
Note that, contrary to what the name suggests, `remove_copy_if` does not actually remove anything. — Baum mit Augen, Nov 18 '16 at 14:46
I actually asked a similar question before. https://stackoverflow.com/questions/27320577/remove-elements-from-range-and-copy-removed-elements-to-new-range — Baum mit Augen, Nov 18 '16 at 14:47
Is your container an actual `std::list`? In that case you should use the `splice` member functions. — Kerrek SB, Nov 18 '16 at 16:20

score 1 · Accepted Answer · answered Nov 18 '16 at 14:44

Use move iterators:

std::remove_copy_if(
    std::make_move_iterator(list.begin()),
    std::make_move_iterator(list.end()),
    std::back_inserter(aux_list),
    [](const value_type& item_ptr) { return !item_ptr->valid(); });

Note that the elements still all exist in list - they weren't actually removed (this is a weirdly named algorithm - think of it as copy_unless()). So now you will have a bunch of elements in an unspecified state.

How to (re)move from a container if predicate is satisfied?

1 Answers1