non-const copy ctor

John Love-Jensen
Sat Apr 8 02:22:00 GMT 2006

Hi Christian,

> Hmm, I would say *usually* it is a const reference.-- But eventually it is
> not, like in my case or in the case of std::auto_ptr.

In C++, a copy constructor is a const reference.

> Of course you could say this isn't a copy constructor because it doesn't take
a const reference.

It's not a copy constructor.

> But I think it is anyway because it still has the semantic of a copy

Regardless, it's not a copy constructor.

> Anyway, I need to have a constructor taking a non-const reference which g++
> doesn't allow.

You can implement similar facilities like auto_ptr for your class to have
the behavior you are inquiring about.

> And I still don't know why g++ is acting this way here and how  to work around

On this particular issue, g++ is complying with ISO 14882.  VC7 is not.

More information in The Design and Evolution of C++:

I don't recall if the particular point you raised is covered.

I believe it (copy constructor being a const reference) has to do with
catastrophic slicing if it were not a const, and infinite recursion if it
were not a reference.


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