stl map question

[Thomas]

I have a question about how the stl map class works. I have a subscription
class that I use to manage client application subscriptions. These are
stored in a map. Periodically, I need to update the subscriptions in the map
to reflect changes to data. When I iterate over the map, I expect to get a
reference to the object stored in the map using

myclass mc = *iter->second;

What I am finding is that the copy constructor is getting invoked resulting
in a copy getting returned instead of a reference.
I tried the alternate approach using the operator[] but get the same
results.

At this point the workaround is to put the modified object back into the map
which seems terribly inefficient.

I checked the SGI website and it looks like it should be returning a
reference and not a copy. But I am not certain.

This is on Solaris 2.8 with 6.2 compiler.

Does this sound correct? Should I expect this to be the defined behavior or
am I missing something?

Thanks,

Thomas

[Buster Copley]

Re: stl map question

Thomas wrote:[color=blue]
> I have a question about how the stl map class works. I have a subscription
> class that I use to manage client application subscriptions. These are
> stored in a map. Periodically, I need to update the subscriptions in the map
> to reflect changes to data. When I iterate over the map, I expect to get a
> reference to the object stored in the map using
>
> myclass mc = *iter->second;[/color]
[snip]

C++ is not Java. This declares an object of class mc and copy-
initializes it from the reference returned by "* (iter->second)".

If you want "mc" to be a reference to a myclass object, declare
it as such:

myclass & mc = * (iter->second);

Regards,
Buster.

[Frank Schmitt]

Re: stl map question

Buster Copley <buster@none.co m> writes:
[color=blue]
> Thomas wrote:[color=green]
> > I have a question about how the stl map class works. I have a subscription
> > class that I use to manage client application subscriptions. These are
> > stored in a map. Periodically, I need to update the subscriptions
> > in the map
> > to reflect changes to data. When I iterate over the map, I expect to get a
> > reference to the object stored in the map using
> > myclass mc = *iter->second;[/color]
> [snip]
>
> C++ is not Java. This declares an object of class mc and copy-
> initializes it from the reference returned by "* (iter->second)".
>
> If you want "mc" to be a reference to a myclass object, declare
> it as such:
>
> myclass & mc = * (iter->second);[/color]

Alternatively, since you seem to store pointers to myclass in the map, just
use pointers:

myclass* mc = iter->second;

regards
frank

--
Frank Schmitt
4SC AG phone: +49 89 700763-0
e-mail: frankNO DOT SPAMschmitt AT 4sc DOT com