This is the mail archive of the
gcc-patches@gcc.gnu.org
mailing list for the GCC project.
Re: [PATCH v2] libstdc++: Add hexfloat/defaultfloat io manipulators.
- From: Luke Allardyce <lukeallardyce at gmail dot com>
- To: Jonathan Wakely <jwakely dot gcc at gmail dot com>
- Cc: Jonathan Wakely <jwakely at redhat dot com>, RÃdiger Sonderfeld <ruediger at c-plusplus dot de>, "libstdc++" <libstdc++ at gcc dot gnu dot org>, gcc-patches <gcc-patches at gcc dot gnu dot org>
- Date: Wed, 16 Apr 2014 14:26:17 +0900
- Subject: Re: [PATCH v2] libstdc++: Add hexfloat/defaultfloat io manipulators.
- Authentication-results: sourceware.org; auth=none
- References: <20140327133723 dot GA13599 at redhat dot com> <1901588 dot qodTErPe42 at descartes> <20140327162714 dot GA13192 at redhat dot com> <CAFW6PZC0u5=i-KqQZZsbkmg5iWr6u2WVnnBQVqG8V2Bt6oOzOg at mail dot gmail dot com> <CAH6eHdTyy5_98zcGCDNOkwTnfmLYHnb+r9m=ktNMCDw2LXWzqA at mail dot gmail dot com>
>> Also the old standard seems to require that ios_base::fixed |
>> ios_base::scientific (or any other combination) falls through to the
>> uppercase test; I was trying to use abi_tag for a solution as not only
>> would two versions of _S_format_float be necessary, but also num_get
>> due to the pre-instantiated templates for <char> and <wchar>, which
>> led me to http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60642. It might
>> just be more trouble than it's worth.
>
> I don't think we need to worry about that, if I understand correctly
> the combination of fixed|scientific has unspecified behaviour in
> C++03, so we can make our implementation do exactly what it does in
> C++11.
It seems to me that it is well defined, going from [lib.facet.num.put.virtuals]
> 6 All tables used in describing stage 1 are ordered. That is, the first line whose condition is true applies.
> A line without a condition is the default behavior when none of the earlier lines apply.
So fixed|scientific would be equivalent to specifying neither
according to table 58, and the resulting specifier would be %g or %G
depending on whether uppercase is set or not.