Re: [boost] [facets] strict_num_put design problem

From: Robert Ramey (ramey_at_[hidden])
Date: 2006-08-22 11:38:14

Johan Råde wrote:

> 3. Formatting always succeeds.

Hmmm - formatting a NaN results in something like "+inf".  Personally, I 
wouldn't characterize that as a success.

<snip>

> This makes it difficult to implement strict_num_put.
> What should it do when validation fails?
> It can not set the failbit of the stream.
> The only thing it can do, is to throw an exception.
> The stream will catch that exception and set the badbit!
> At least with VC++ 7.1.

Its better than nothing.  Personally I would be fine with this.

> Why? The stream probably assumes that formatting facets do not throw
> exceptions,
> so it concludes that the exception was thrown by the stream buffer.
> When the stream buffer is corrupted, the stream sets the badbit.

> However, setting the badbit when data validation fails, is a bad idea.

How come?

>
>    Suggested solution:
>      Throw out the facets strict_num_put and strict_num_get.
>
>    Comments?

You've already investigated the issue more than I have so I'm happy to defer 
to your judgement.

On the other hand, the attempt to serialize a NaN is an indication of a 
broken program I would like to see it trapable.  On the other hand, it seems 
that I'm the only one who thinks this.  Oh well.

>
> The documentation of the library has been updated to reflect this
> problem.

thanks for taking this on.

Robert Ramey