[cfe-dev] [libc++] Is namespace "index" a special kind of a namespace in libc++?

[Richard Smith via cfe-dev]

On 31 October 2017 at 05:00, Klemen Forstnerič via cfe-dev <
cfe-dev at lists.llvm.org> wrote:

> Thanks for your reply. When I try to build my previously posted example
> (index.hpp and index.cpp) with the flags "-U_GNU_SOURCE -D_ISOC99_SOURCE"
> it works, but when I try it on my production code, I get random errors in
> all sorts of places. Having tried that, is there anything else I can do,
> besides renaming my namespace index to something else?
>
> Should I have rebuilt libc++ itself with those flags instead of my code?
>

No, you did the right thing. Most likely either your code or one of your
dependencies (maybe even libc++) depends on an extension that's disabled by
-U_GNU_SOURCE. If you can figure out which one, you should be able to
re-enable that extension with the relevant *_SOURCE macro.


> I should note, though, using the command "clang++ index.cpp" (which uses
> the system's libstdc++ 4.8) to build my previously posted example, doesn't
> require me to undefine _GNU_SOURCE and define _ISOC99_SOURCE to make it
> compile. What does libstdc++ do differently than libc++?
>

Its <algorithm> header presumably has a different set of #includes.


> Thanks again.
>
> On Tue, Oct 31, 2017 at 12:04 AM, Richard Smith <richard at metafoo.co.uk>
> wrote:
>
>> On 30 October 2017 at 07:52, Klemen Forstnerič via cfe-dev <
>> cfe-dev at lists.llvm.org> wrote:
>>
>>> Hi Richard,
>>>
>>> thanks replying. So if I understood correctly, undefining _GNU_SOURCE
>>> and defining _ISOC99_SOURCE instead, should be a good fix until this
>>> gets patched in libc++? :-)
>>>
>>
>> There's nothing that libc++ can do about it; the 'index' function is
>> coming from your libc implementation. But yes, undefining _GNU_SOURCE and
>> defining _ISOC99_SOURCE (and maybe also _ISOC11_SOURCE) should probably
>> work.
>>
>>
>>> Cheers,
>>> Klemen
>>>
>>> On Sun, Oct 29, 2017 at 11:14 PM, Richard Smith <richard at metafoo.co.uk>
>>> wrote:
>>>
>>>> Looks like glibc provides it in <string.h> too if _GNU_SOURCE is
>>>> defined, which it *always* is when compiling in C++ mode (unless explicitly
>>>> undefined). :-(
>>>>
>>>> Is it still the case that glibc requires _GNU_SOURCE to be defined in
>>>> order for it to provide the symbols that C++ compilation requires? A quick
>>>> test seems to show that _ISOC99_SOURCE (or sometimes _ISOC11_SOURCE) is
>>>> actually sufficient. Perhaps we should provide a mode that doesn't define
>>>> _GNU_SOURCE (ideally, -std=c++XX would have that effect, but that's
>>>> probably going to break too much).
>>>>
>>>>
>>>> On 29 October 2017 at 13:14, Richard Smith <richard at metafoo.co.uk>
>>>> wrote:
>>>>
>>>>> There is a ::index function in strings.h on some platforms that might
>>>>> be leaking into <algorithm>.
>>>>>
>>>>> On 29 Oct 2017 13:10, "Klemen Forstnerič via cfe-dev" <
>>>>> cfe-dev at lists.llvm.org> wrote:
>>>>>
>>>>> Hi libc++ developers,
>>>>>
>>>>> I'm having a problem compiling the following code:
>>>>>
>>>>> Header (index.hpp):
>>>>>
>>>>> #ifndef INDEX_HPP_
>>>>> #define INDEX_HPP_
>>>>>
>>>>> #include <algorithm>
>>>>>
>>>>> namespace index {
>>>>>
>>>>> class Index {
>>>>>  public:
>>>>>   Index();
>>>>> };
>>>>>
>>>>> }
>>>>>
>>>>> #endif // INDEX_HPP_
>>>>>
>>>>> Source (index.cpp):
>>>>>
>>>>> #include "index.hpp"
>>>>>
>>>>> namespace index {
>>>>>
>>>>> Index::Index() {
>>>>> }
>>>>>
>>>>> }
>>>>>
>>>>> These are the errors I get:
>>>>>
>>>>> index.cpp:5:1: error: use of undeclared identifier 'Index'; did you
>>>>> mean '::index::Index'?
>>>>> Index::Index() {
>>>>> ^~~~~
>>>>> ::index::Index
>>>>> ./index.hpp:8:7: note: '::index::Index' declared here
>>>>> class Index {
>>>>>       ^
>>>>> index.cpp:5:8: error: cannot define or redeclare 'Index' here because
>>>>> namespace 'index' does not enclose namespace 'Index'
>>>>> Index::Index() {
>>>>> ~~~~~~~^
>>>>> 2 errors generated.
>>>>>
>>>>> This is my compile command:
>>>>> clang++ --stdlib=libc++ index.cpp
>>>>>
>>>>> clang version:
>>>>> clang version 5.0.0 (tags/RELEASE_500/final)
>>>>> Target: x86_64-unknown-linux-gnu
>>>>> Thread model: posix
>>>>> InstalledDir: /usr/local/bin
>>>>>
>>>>> libc++ version is today's trunk
>>>>>
>>>>> System: Linux trusty64 3.16.0-55-generic #74~14.04.1-Ubuntu SMP Tue
>>>>> Nov 17 10:15:59 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux
>>>>>
>>>>>
>>>>> If I don't include <algorithm> or if I change the name of the
>>>>> namespace to something other than "index", the code compiles.
>>>>>
>>>>> Is this a libc++ bug?
>>>>>
>>>>> Cheers,
>>>>> Klemen
>>>>>
>>>>> _______________________________________________
>>>>> cfe-dev mailing list
>>>>> cfe-dev at lists.llvm.org
>>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
>>>>>
>>>>>
>>>>>
>>>>
>>>
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>>
>
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