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Re: [patch] Leave errno unchanged by successful std::stoi etc
- From: Jakub Jelinek <jakub at redhat dot com>
- To: Jonathan Wakely <jwakely at redhat dot com>
- Cc: libstdc++ at gcc dot gnu dot org, gcc-patches at gcc dot gnu dot org
- Date: Tue, 29 Sep 2015 17:25:15 +0200
- Subject: Re: [patch] Leave errno unchanged by successful std::stoi etc
- Authentication-results: sourceware.org; auth=none
- References: <20150929151541 dot GZ12094 at redhat dot com>
- Reply-to: Jakub Jelinek <jakub at redhat dot 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