Is clang's c++11 support reliable? - c++

Question

I ran into an interesting issue when trying to mix clang (Apple LLVM version 6.0 (clang-600.0.56) (based on LLVM 3.5svn, Target: x86_64-apple-darwin14.0.0), c++11 and CGAL (via MacPorts).
It seems that whether or not I call std::vector<>::reserve will determine whether my program will even compile.
I've trimmed down the problem into a minimal example (as minimal as CGAL examples get):
#include <vector>
#include <CGAL/Exact_predicates_inexact_constructions_kernel.h>
#include <CGAL/AABB_tree.h>
#include <CGAL/AABB_traits.h>
#include <CGAL/AABB_triangle_primitive.h>
// CGAL::Epeck works fine, suggesting the problem is in CGAL::Epick
typedef CGAL::Epick Kernel;
typedef CGAL::Triangle_3<Kernel> Triangle_3;
typedef typename std::vector<Triangle_3>::iterator Iterator;
typedef CGAL::AABB_triangle_primitive<Kernel, Iterator> Primitive;
typedef CGAL::AABB_traits<Kernel, Primitive> AABB_triangle_traits;
typedef CGAL::AABB_tree<AABB_triangle_traits> Tree;
typedef typename Tree::Point_and_primitive_id Point_and_primitive_id;
typedef CGAL::Point_3<Kernel> Point_3;
template <typename BKernel>
void A()
{
const CGAL::AABB_tree<
CGAL::AABB_traits<BKernel,
CGAL::AABB_triangle_primitive<BKernel,
typename std::vector<CGAL::Triangle_3<BKernel> >::iterator
>
>
> tree;
Point_and_primitive_id pp = tree.closest_point_and_primitive(Point_3());
}
void B()
{
std::vector<Triangle_3> T;
#ifdef MAGIC
T.reserve(0);
#endif
return A<Kernel>();
}
Issuing:
clang++ -std=c++11 -c example.cpp -I/opt/local/include
This fails to compile. Giving errors like:
In file included from example.cpp:1:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/vector:265:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/__bit_reference:15:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/algorithm:626:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/utility:157:
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/__tuple:228:60: error:
no member named 'value' in 'std::__1::is_convertible<const CGAL::Point_3<CGAL::Epick> &,
CGAL::Point_3<CGAL::Epick> >'
is_convertible<_Tp0, _Up0>::value &&
~~~~~~~~~~~~~~~~~~~~~~~~~~~~^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/__tuple:242:14: note:
in instantiation of template class 'std::__1::__tuple_convertible_imp<true, std::__1::__tuple_types<const
CGAL::Point_3<CGAL::Epick> &, const CGAL::Vector_3<CGAL::Epick> &>,
std::__1::__tuple_types<CGAL::Point_3<CGAL::Epick>, CGAL::Vector_3<CGAL::Epick> > >' requested here
: public __tuple_convertible_imp<tuple_size<typename remove_reference<_Tp>::type>::value ==
However, this does compile if I make this magic call to std::vector::reserve, issuing:
clang++ -std=c++11 -c example.cpp -I/opt/local/include -DMAGIC
or by disabling c++11
clang++ -c example.cpp -I/opt/local/include
Is this a bug in CGAL or clang?
What explanation can there be for such erratic compiler behavior?
Is there a clean way of avoiding this (hopefully without really changing the templating or function prototype set up as I need the solution to fit my larger project).

Answer 1

Since Apple's GCC is outdated (latest GPL v2 version from 2007, GCC 4.2.1) and not C++11 feature complete (hence the libstdc++ provided with it), you can install a more modern version of GCC through MacPorts (sudo port install gcc48 or sudo port install gcc49) and that will provide you a more modern version of libstdc++. I tested your code with:
/opt/local/bin/g++-mp-4.8 -std=c++11 -c example.cpp -I/opt/local/include
and it compiled succesfully.
If you prefer this solution and want a cleaner compiler call; you can set MacPorts' GCC as the default using gcc_select with the command (in my case for gcc48):
sudo port select --set gcc mp-gcc48
only once. Then, you can compile it with just
g++ -std=c++11 -c example.cpp -I/opt/local/include
in a new terminal session.