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]

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;

[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]

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;

[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);

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

myclass* mc = iter->second;

regards
frank