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

[Jakub Jelinek <jakub@redhat.com>]

On Tue, Sep 29, 2015 at 04:15:41PM +0100, Jonathan Wakely wrote:
> We set errno=0 in __gnu_cxx::__stoa in order to reliably detect when
> it gets set to ERANGE. This restores the previous value when the
> conversion is successful.
> 
> Tested powerpc64le-linux, committed to trunk.

> commit 412f75dc37b1048e14996c9caafa46c00db8eb30
> Author: Jonathan Wakely <jwakely@redhat.com>
> Date:   Tue Sep 29 15:09:23 2015 +0100
> 
>     Leave errno unchanged by successful std::stoi etc
>     
>     	* include/ext/string_conversions.h (__stoa): Save and restore errno.
>     	* testsuite/21_strings/basic_string/numeric_conversions/char/errno.cc:
>     	New.
> 
> diff --git a/libstdc++-v3/include/ext/string_conversions.h b/libstdc++-v3/include/ext/string_conversions.h
> index f4648a8..58387a2 100644
> --- a/libstdc++-v3/include/ext/string_conversions.h
> +++ b/libstdc++-v3/include/ext/string_conversions.h
> @@ -58,6 +58,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>        _Ret __ret;
>  
>        _CharT* __endptr;
> +      const int __saved_errno = errno;
>        errno = 0;
>        const _TRet __tmp = __convf(__str, &__endptr, __base...);
>  
> @@ -70,6 +71,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>  	std::__throw_out_of_range(__name);
>        else
>  	__ret = __tmp;
> +      errno = __saved_errno;

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.
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.

	Jakub