Re: [gentoo-musl] [GSoC] _GNU_SOURCE in C++

[Lei Zhang]

2016-06-21 12:54 GMT+08:00 Lei Zhang <zhanglei.april@×××××.com>:
> 2016-06-17 20:44 GMT+08:00 Lei Zhang <zhanglei.april@×××××.com>:
>> After putting about eight "#define _GNU_SOURCE"s in various *.cpp
>> files, it seems to work now :)
>
> I was wrong; it doesn't work... I still can't figure out a good solution :(
>
> Take glibc's strtoll_l for example: it's hidden by _GNU_SOURCE in
> stdlib.h and used exclusively by libc++'s header <locale>; but
> defining _GNU_SOURCE in <locale> could be too late, since stdlib.h
> might be included prior to <locale>.
>
> Though glibc's stdlib.h is only explicitly included in <cstdlib>,
> defining _GNU_SOURCE in <cstdlib> doesn't work either. It turns out
> strtoll_l (and others) is not directly protected by _GNU_SOURCE, but
> by __USE_GNU, which is in turn defined in features.h according to
> _GNU_SOURCE. That means "#define _GNU_SOURCE" must appear before the
> inclusion of features.h, and it's not very clear where "#undef
> _GNU_SOURCE" should be put.
>
> Any suggestions?

So far the only feasible solution I can think of is to wrap every
inclusion of C headers in libc++ with a pair of "#define _GNU_SOURCE"
and "#undef _GNU_SOURCE", thus making sure _GNU_SOURCE is defined
before any implicitly inclusion of features.h. It is cumbersome, but
works. I haven't really figured out if this solution is 100%
error-proof.

P.S.: sorry for my previous mis-sent message.


Lei