Clang,std :: shared_ptr和std :: less/operator <

Question

拥有以下代码

#include <memory>

int main() {
    std::shared_ptr<int> ptr0( new int );
    std::shared_ptr<int> ptr1( new int );

    bool result = ptr0 < ptr1;
}

使用clang编译时产生以下错误(版本3.1,LLVM 3.1,Debian GNU/Linux Sid)

/usr/bin/../lib/gcc/x86_64-linux-gnu/4.7/../../../../include/c++/4.7/bits/shared_ptr.h:364:14: error: no matching function for call to object of type 'std::less<_CT>'
      return std::less<_CT>()(__a.get(), __b.get());
             ^~~~~~~~~~~~~~~~
foo.cpp:9:21: note: in instantiation of function template specialization 'std::operator<<int, int>' requested here
        bool result = ptr0 < ptr1;
                           ^
/usr/bin/../lib/gcc/x86_64-linux-gnu/4.7/../../../../include/c++/4.7/bits/stl_function.h:236:7: note: candidate function not viable: no known conversion from 'int *' to 'int *&&&' for
      1st argument;
      operator()(const _Tp& __x, const _Tp& __y) const
      ^

使用GCC(版本4.7.0)编译相同的代码不会抛出任何错误消息.运算符<()是否适用于clang中的共享指针？

Answer 1

clang ++和libstdc ++完全不匹配.您可以执行以下操作之一:

• 切换到libc ++(使用clang++ -stdlib=libc++ -std=c++11 ...)

• 应用以下补丁/usr/include/c++/4.7.0/type_traits(如http://clang.llvm.org/cxx_status.html中所述):

  Index: include/std/type_traits
  ===================================================================
  --- include/std/type_traits (revision 185724)
  +++ include/std/type_traits (working copy)
  @@ -1746,7 +1746,7 @@
  
     template<typename _Tp, typename _Up>
       struct common_type<_Tp, _Up>
  -    { typedef decltype(true ? declval<_Tp>() : declval<_Up>()) type; };
  +    { typedef typename decay<decltype(true ? declval<_Tp>() : declval<_Up>())>::type type; };
  
     template<typename _Tp, typename _Up, typename... _Vp>
       struct common_type<_Tp, _Up, _Vp...>
  

如果你检查bits/shared_ptr.h确实发现了std::common_type,并且clang开发人员声称它实际上是libstdc ++的一个错误,虽然我不相信libstdc ++的错误会导致不存在的类型int*&&&出现.