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From: jpotter@falcon.lhup.edu (John Potter)
Newsgroups: comp.std.c++
Subject: Re: Are literals const?
Date: Thu, 23 Aug 2001 21:33:24 GMT
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On Wed, 22 Aug 2001 20:17:28 GMT, pdimov@mmltd.net (Peter Dimov) wrote:

> What do you think about this piece of code:
> 
> int main()
> {
>   int const & r = 5;
>   const_cast<int &>(r) = 6;
> }
> 
> Is this legal? I think that it is. Literals aren't const (they are
> about 90% const, but not 100% const.)

Sure, its "legal", with undefined behaviour.

> Similarly:
> 
> int f()
> {
>   return 5;
> }
> 
> int main()
> {
>   int const & r = f();
>   const_cast<int &>(r) = 6;
> }

Same here.

Read the fine print on binding a const& to an rvalue.  In the case of
built-ins, a temporary is required.  The temporary may be of const
type and removing const from a const object gives undefined behaviour.
The undefined behaviour usually does what you expect because the temp
is not really in read only memory.  Playing with fire is fun. ;-)

John

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