[英]Self-referential use of unordered_map causes problems for gcc 5.3 but not clang
以下代码无法在gcc 5.3下编译 (这是从较大代码段中获取的简化版本):
#include <unordered_map>
#include <string>
class Foo {
std::unordered_map<std::string, Foo> m; //"self-referential"
};
int main()
{
Foo f;
return 0;
}
出现以下错误:
g++ --std=c++1y -c rh.cpp
In file included from /usr/local/include/c++/5.3.0/utility:70:0,
from /usr/local/include/c++/5.3.0/unordered_map:38,
from rh.cpp:1:
/usr/local/include/c++/5.3.0/bits/stl_pair.h: In instantiation of ‘struct std::pair<const int, Foo>’:
/usr/local/include/c++/5.3.0/ext/aligned_buffer.h:85:34: required from ‘struct __gnu_cxx::__aligned_buffer<std::pair<const int, Foo> >’
/usr/local/include/c++/5.3.0/bits/hashtable_policy.h:246:43: required from ‘struct std::__detail::_Hash_node_value_base<std::pair<const int, Foo> >’
/usr/local/include/c++/5.3.0/bits/hashtable_policy.h:292:12: required from ‘struct std::__detail::_Hash_node<std::pair<const int, Foo>, false>’
/usr/local/include/c++/5.3.0/bits/hashtable_policy.h:1896:60: required from ‘struct std::__detail::_Hashtable_alloc<std::allocator<std::__detail::_Hash_node<std::pair<const int, Foo>, false> > >’
/usr/local/include/c++/5.3.0/bits/hashtable.h:170:11: required from ‘class std::_Hashtable<int, std::pair<const int, Foo>, std::allocator<std::pair<const int, Foo> >, std::__detail::_Select1st, std::equal_to<int>, std::hash<int>, std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash, std::__detail::_Prime_rehash_policy, std::__detail::_Hashtable_traits<false, false, true> >’
/usr/local/include/c++/5.3.0/bits/unordered_map.h:101:18: required from ‘class std::unordered_map<int, Foo>’
rh.cpp:4:32: required from here
/usr/local/include/c++/5.3.0/bits/stl_pair.h:102:11: error: ‘std::pair<_T1, _T2>::second’ has incomplete type
_T2 second; /// @c second is a copy of the second object
^
rh.cpp:3:7: note: forward declaration of ‘class Foo’
class Foo {
使用clang的代码没有问题(我在Linux上测试了3.8,在OSX上测试了3.9):
clang++ --std=c++1y --stdlib=libc++ -c rh.cpp
在Linux上,使用clang + libstdc ++也会失败。
问题似乎归结为在其哈希映射实现中使用__gnu_cxx::__aligned_buffer
libstdc ++ ,它需要完整的类型。
当使用std :: map时,两个标准库都可以正常工作,但这不是我可以接受的解决方案。 映射的值类型也不是指向Foo的指针。
为了使代码在gcc / libstdc ++上运行,我还可以进行其他更改吗?
谢谢!
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