[cfe-dev] Current state of libcxx compatibility with libstdc++
Jonathan Roelofs via cfe-dev
cfe-dev at lists.llvm.org
Tue Aug 9 06:53:24 PDT 2016
On 8/9/16 4:03 AM, Jeroen Ooms via cfe-dev wrote:
> [ This is probably a FAQ, however Google gives a lot of conflicting and
> outdated information... ]
> We are trying to add support for compiling R packages with C++11 code on
> CentOS 6/7 using standard compilers from CentOS/EPEL repositories.
> Because gcc/libstdc++ on CentOS are too old (4.4.7), Tom Callaway has
> recently added libcxx and libcxxabi [1,2] to Fedora/EPEL. We can now
> build C++11 code natively on CentOS with clang:
> clang++ -stdlib=libc++ -std=c++11 example.cpp
> Awesome. However for code which links to c++ system libraries (which are
> compiled with gcc) this sometimes results in linking errors. For example
> a test application geometry.cpp  which links to the
> "ImageMagick-c++-devel" package:
> clang++ -stdlib=libc++ -std=c++11 geometry.cpp $(pkg-config --cflags
> --libs ImageMagick++)'
> This fails with:
> geometry.cpp:(.text+0xd9): undefined reference to
> std::__1::char_traits<char>, std::__1::allocator<char> > const&)'
> geometry.cpp:(.text+0x2ed): undefined reference to
> `Magick::Geometry::operator std::__1::basic_string<char,
> std::__1::char_traits<char>, std::__1::allocator<char> >() const'
> Is this expected?
> Is there any way we can work around this to link c++
> programs compiled with libcxx against system libraries which are
> compiled with gcc?
"compiled with gcc" isn't the issue. The issue is that you have one set
of objects *built against libstdc++* and you're trying to link them
against another set *built against libcxx*. This can only work if your
interface between them does not contain things from the standard library.
Let me re-iterate: it is ok to link against both standard libraries
(their symbols won't collide). What's not going to work is to use the
headers from one library against the binaries from the other.
> If not, might this be possible for future versions of
> libcxx or are the two simply incompatible on this level?
The compatibility you're looking for here is never going to happen.
>  https://bugzilla.redhat.com/show_bug.cgi?id=1332306
>  https://bugzilla.redhat.com/show_bug.cgi?id=1332307
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> cfe-dev at lists.llvm.org
jonathan at codesourcery.com
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