[cfe-dev] [libcxx] C++03 support level?

[Eric Fiselier via cfe-dev]

> It is my understanding that libc++ is fully C++03 compatible. Or is this
not the case? (I couldn't find this fact explicitly documented on
libcxx.llvm.org).

We don't provide a  conforming C++03 mode.
Libc++ uses the C++11  as its base document. C++03 support is really just
the C++11 STL without C++11 language features.

> If the underlying C-library does not provide those C99 functions (as
expected for -std=C++03), this usage will result in a compiler error.

That's problematic. If a header exists in C++03 then users should be able
to include it without error in C++03.
If certain C libraries require extra guards around C99 declarations then we
should support that.
However most C libraries provide the C99 extensions in C++03 and libc++
should continue to provide them as well.

>  Do we need to be more lenient with libc++?

Probably not. I think we should fix libc++ to support strict C library
implementations.

> Or is this a regression from D12747?

I don't think it's a regression because we never provided strict C++03
conformance.

> If there is a common senses on this, I'd like to at least document in on
libcxx.llvm.org.

Agreed. I'll work on creating some docs.

/Eric

On Thu, Aug 25, 2016 at 8:47 AM, Asiri Rathnayake <
asiri.rathnayake at gmail.com> wrote:

> Hi All,
>
> I've got a couple of questions:
>
> It is my understanding that libc++ is fully C++03 compatible. Or is this
> not the case? (I couldn't find this fact explicitly documented on
> libcxx.llvm.org).
>
> Following the split of <cfoo> headers into <cfoo> and <foo.h> headers in
> [1], any compilation including <foo.h> will end up picking the libc++
> header instead of directly including the underlying C library's <foo.h>
> header. This can be a bit problematic for -std=c++03 in some cases. For
> example, <math.h> header provided by libc++ makes references C99 math
> functions unconditionally, which is OK for -std=c++11 and beyond, but not
> OK for -std=c++03. If the underlying C-library does not provide those C99
> functions (as expected for -std=C++03), this usage will result in a
> compiler error.
>
> Am I missing something here? We have a C library which is quite strict
> about standards conformance (e.g. it won't make C99 math functions visible
> if being used under -std=c++03). Do we need to be more lenient with libc++?
> Or is this a regression from D12747?
>
> If there is a common senses on this, I'd like to at least document in on
> libcxx.llvm.org.
>
> Thanks.
>
> / Asiri
>
> [1] https://reviews.llvm.org/D12747
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/cfe-dev/attachments/20160828/bd2bc625/attachment.html>