Re: [patch] Leave errno unchanged by successful std::stoi etc

[Jakub Jelinek <jakub@redhat.com>]

On Tue, Sep 29, 2015 at 05:10:20PM +0100, Jonathan Wakely wrote:
> >That looks wrong to me, you only restore errno if you don't throw :(.
> >If you throw, then errno might remain 0, which is IMHO undesirable.
> 
> My thinking was that a failed conversion that throws an exception
> should be allowed to modify errno, and that the second case sets it to
> ERANGE sometimes anyway.

Well, you can modify errno, you just shouldn't change it from non-zero to
zero as far as the user is concerned.

http://pubs.opengroup.org/onlinepubs/009695399/functions/errno.html
"No function in this volume of IEEE Std 1003.1-2001 shall set errno to 0."
Of course, this part of STL is not POSIX, still, as you said, it would be
nice to guarantee the same.
> 
> But I suppose it would be better to consistently set it to non-zero
> when an exception is thrown, or consistently restore the original
> value in all cases.
> 
> >So, I'd say you want to restore it earlier, right after __convf, and
> >immediately before that copy the current errno to some other temporary
> >for the use in the condition?  Or restore errno = __saved_errno;
> >in all the 3 spots instead of just one.
> 
> Or in a destructor so it happens however we exit the function, like
> this ...

Works for me.

	Jakub