[boost] Re: Re: about change to lexical_cast

From: Stéphane Bronsart (stephane.bronsart_at_[hidden])
Date: 2002-07-24 05:11:48

Ok, I'm agree with you that the error is well in the STLPort 4.5.3.
But from now, what can I do ?
Is some developers from STLPort aware about that ?  If no, how comminucate
with them about this bug ?

Thank a lot for all.
Stéphane.

"Terje Slettebø" <tslettebo_at_[hidden]> wrote in message
news:0b0a01c232f5$e3ba2a00$60fb5dd5_at_pc...
>From: "Stéphane Bronsart" <stephane.bronsart_at_[hidden]>

> A signed long can hold value from -2147483648 to 2147483647
>
> signed long l;
>
> 1) l=lexical_cast<signed long>("2147483647"); // Ok l = 2147483647
> 2) l=lexical_cast<signed long>("2147483648"); // False : no exception
>                                                                         //
> and l = -2147483648
> 3) l=lexical_cast<signed long>("2147483650"); // OK exception occurs
>
> > Why case 2 don't throw exception and case 3 yes ?
> > If lexical_cast throw exption with a value 3 unit greater than the
limit,
> > why not with a value 1 greater than the limit ?
>
> Kevlin say : "Some they the error is in the stream operator for long in
the
> STLport 4.5.3."

Like I said in the earlier thread, I agree with Kevlin. The error is in the
library, with stringstream, not lexical_cast.

I tried it now, here. STLPort gives the above error, while the MSVC library
gives exception when it's suppposed to, also in the second case above.

Regards,

Terje

> "Terje Slettebø" <tslettebo_at_[hidden]> wrote in message
> news:0a5901c232ec$5d7785e0$60fb5dd5_at_pc...
> >From: "Stéphane Bronsart" <stephane.bronsart_at_[hidden]>
>
> > Some week ago, I've alerted about a problem using lexical_cast with
signed
> > number.
> >
> > ex : signed int number = lexical_cast<signed int>("60000");
> > return a bad value (the complement) without throwing an exception.
> >
> > Kevlin email me that that the real problem was certainly in the "local"
> > implementation (used by iostream, thus by lexical_cast).  How to solve
> these
> > problem.  Who is responsible for that.  Who will correct it ?
>
> Like it was mentioned in that thread, you can use something like this:
>
> template<class Target, class Source>
> Target checked_lexical_cast(Source arg)
> {
>   long l=boost::lexical_cast<long>(arg);
>
>   return boost::numeric_cast<Target>(l);
> }
>
> At least this works for integers. A problem here is that when it reads the
> value from the string, like "60000", it doesn't know how big the value
will
> be, or what kind of value it is. It needs to be told that. So, above here,
> "long" is used, as it should be able able to handle all integers. Then,
you
> may use a checked conversion like numeric_cast, to convert this to the
> required type.
>
> Anybody else have any ideas about this?
>
>
> Regards,
>
> Terje

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