具有clang ++ v4和gcc 6.3库的自定义分配器

Question

在带有gcc 6.3.1的库的系统（arch linux）上，将自定义分配器与clang ++ 4.0.0一起使用时，我遇到了很多麻烦。 这是一个最小的无效示例：

#include <string>

struct myalloc : std::allocator<char> {
  using std::allocator<char>::allocator;
};

struct mystring 
  : std::basic_string<char, std::char_traits<char>, myalloc> {
  using std::basic_string<char, std::char_traits<char>, myalloc>::basic_string;
};

int
main()
{
  mystring r = "hello";
  mystring s (std::move(r));
}

我的意图显然是让myalloc是一个自定义分配器，其行为与系统std::allocator完全相同，而mystring与std::string相同，只是它使用myalloc 。 这应该是引起问题的可能性最小的情况。 （很显然，一旦这起作用了，我想进一步自定义分配器。）

代码可以使用g++ -std=c++14 -Wall -Werror干净地编译，但是clang++ -std=c++14失败并显示：

In file included from strerror.cc:1:
In file included from /usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/6.3.1/../../../../include/c++/6.3.1/string:52:
/usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/6.3.1/../../../../include/c++/6.3.1/bits/basic_string.h:477:9: error: 
      no matching constructor for initialization of
      'std::__cxx11::basic_string<char, std::char_traits<char>,
      myalloc>::_Alloc_hider'
      : _M_dataplus(_M_local_data(), std::move(__str._M_get_allocator()))
        ^           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
strerror.cc:7:8: note: in instantiation of member function
      'std::__cxx11::basic_string<char, std::char_traits<char>,
      myalloc>::basic_string' requested here
struct mystring 
       ^
/usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/6.3.1/../../../../include/c++/6.3.1/bits/basic_string.h:109:2: note: 
      candidate constructor not viable: no known conversion from 'typename
      std::remove_reference<allocator<char> &>::type' (aka
      'std::allocator<char>') to 'const myalloc' for 2nd argument
        _Alloc_hider(pointer __dat, const _Alloc& __a = _Alloc())
        ^
/usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/6.3.1/../../../../include/c++/6.3.1/bits/basic_string.h:107:14: note: 
      candidate constructor (the implicit move constructor) not viable: requires
      1 argument, but 2 were provided
      struct _Alloc_hider : allocator_type // TODO check __is_final
             ^
/usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/6.3.1/../../../../include/c++/6.3.1/bits/basic_string.h:107:14: note: 
      candidate constructor (the implicit copy constructor) not viable: requires
      1 argument, but 2 were provided
1 error generated.

这仅仅是clang或gcc库中的错误，还是我的代码在概念上有问题？

Answer 1

对您的最小示例的最小修复是添加此成员以struct myalloc

template<class> struct rebind {
    using other = myalloc;
};

当然，最好不要继承自std :: allocator（在这种情况下，您无需重新绑定），也不要继承自字符串，这些类都不打算用作公共基础。