Re: multimap and abstract class

James Kanze <>
Fri, 21 Aug 2009 02:44:27 -0700 (PDT)
asOn Aug 20, 10:30 am, Barry <> wrote:

I have an abstract class called "Event" and a number of
classes which inherit from it, including "NoteOn" and

I am now attempting to create a multimap called EventList, as
follows -

#ifndef EVENT_LIST_H

#include <map>
#include "Event.h"

class EventList : public std::multimap<double,Event>
        virtual ~EventList(void);

#ifndef EVENT_H

class Event
        virtual void dummy() = 0;
        virtual ~Event(void);

but this isn't allowed according to my compiler because
'Event' : cannot instantiate abstract class.

I don't understand why I get this fail since I haven't even
created a EventList object yet.

What is the issue here?

You've used std::multimap< double, Event > in a context where a
complete type definition is required, so you've instantiated the
class template. The standard says that this is undefined
behavior if you do it over a type which doesn't support a
minimum of required operations: copy construction and
assignment, for example. An abstract class doesn't fit the
bill, so the compiler can do anything it wants. Good compilers
(or library implementations) generate a compile time error.

James Kanze (GABI Software)
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