On Wed, 28 Jan 2026 at 09:45, Tomasz Kaminski <[email protected]> wrote:
>
>
>
> On Tue, Jan 27, 2026 at 7:15 PM Jonathan Wakely <[email protected]> wrote:
>>
>> On targets where wchar_t is unsigned we get warnings during the
>> libstdc++ build:
>>
>> ctype_members.cc: In member function ‘virtual char
>> std::ctype<wchar_t>::do_narrow(wchar_t, char) const’:
>> ctype_members.cc:224:14: warning: comparison of unsigned expression in ‘>=
>> 0’ is always true [-Wtype-limits]
>> 224 | if (__wc >= 0 && __wc < 128 && _M_narrow_ok)
>> | ~~~~~^~~~
>> ctype_members.cc: In member function ‘virtual const wchar_t*
>> std::ctype<wchar_t>::do_narrow(const wchar_t*, const wchar_t*, char, char*)
>> const’:
>> ctype_members.cc:247:21: warning: comparison of unsigned expression in ‘>=
>> 0’ is always true [-Wtype-limits]
>> 247 | if (*__lo >= 0 && *__lo < 128)
>> | ~~~~~~^~~~
>>
>> This introduces a helper function that converts the wchar_t to an
>> unsigned type and then does the comparison. This means the comparison is
>> not target-dependent, and there's no more warning.
>>
>> libstdc++-v3/ChangeLog:
>>
>> * config/locale/gnu/ctype_members.cc (use_table): New function.
>> (ctype<wchar_t>::do_narrow): Use use_table.
>> ---
>>
>> Tested x86_64-linux and aarch64-linux.
>
> LGTM, assuming using C++11 features is fine (see question below).
>>
>>
>>
>>
>> libstdc++-v3/config/locale/gnu/ctype_members.cc | 13 +++++++++++--
>> 1 file changed, 11 insertions(+), 2 deletions(-)
>>
>> diff --git a/libstdc++-v3/config/locale/gnu/ctype_members.cc
>> b/libstdc++-v3/config/locale/gnu/ctype_members.cc
>> index 183babb6c3f6..b34446a61ee1 100644
>> --- a/libstdc++-v3/config/locale/gnu/ctype_members.cc
>> +++ b/libstdc++-v3/config/locale/gnu/ctype_members.cc
>> @@ -217,11 +217,20 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>> return __hi;
>> }
>>
>> + // True if c can be looked up in _M_narrow.
>> + [[gnu::always_inline]]
>> + static inline bool
>> + use_table(wchar_t c)
>> + {
>> + using U = std::make_unsigned<wchar_t>::type;
>
> This is C++11 feature, and ctype facet in C++98, so at first glance this
> seems like a problem.
> However, this is part of the object file and it is compiled during build, so
> it strictly depends on what standard
> we compile the source file. What is the approach here? If it is documented
> somewhere, just drop a link.
These files are built by src/c++11/Makefile.am
# Source files linked in via configuration/make substitution for a
# particular host.
host_sources = \
ctype_configure_char.cc \
ctype_members.cc
ctype_configure_char.cc:
${glibcxx_srcdir}/$(OS_INC_SRCDIR)/ctype_configure_char.cc
$(LN_S) ${glibcxx_srcdir}/$(OS_INC_SRCDIR)/ctype_configure_char.cc
. || true
ctype_members.cc: ${glibcxx_srcdir}/$(CCTYPE_CC)
$(LN_S) ${glibcxx_srcdir}/$(CCTYPE_CC) . || true
And the objects built by that makefile are compiled with:
AM_CXXFLAGS = \
-std=gnu++11 \
