关于c ++：是否有理由为什么std :: make_shared需要默认的构造函数？

is there a reason why std::make_shared would require a default constructor?

我试图找出这是否是谷物的要求。

我一直在收到错误，因为类构造器(默认构造器)是私有的，我将其放置在这里是有原因的。

但是，错误的始发行似乎是std :: make_shared，而不是谷物，后者需要默认构造函数，但已经是一个朋友类，因此应该可以访问它。

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/usr/include/c++/4.7/type_traits: In instantiation of ‘struct std::__is_default_constructible_impl<Concept>’:
/usr/include/c++/4.7/type_traits:116:12: required from ‘struct std::__and_<std::__not_<std::is_void<Concept> >, std::__is_default_constructible_impl<Concept> >’
/usr/include/c++/4.7/type_traits:682:12: required from ‘struct std::__is_default_constructible_atom<Concept>’
/usr/include/c++/4.7/type_traits:703:12: required from ‘struct std::__is_default_constructible_safe<Concept, false>’
/usr/include/c++/4.7/type_traits:709:12: required from ‘struct std::is_default_constructible<Concept>’
/usr/local/include/cereal/types/polymorphic.hpp:157:5: required by substitution of ‘template<class Archive, class T> typename std::enable_if<((! std::is_default_constructible< T >::value) && (! has_load_and_allocate<T, Archive>())), bool>::type cereal::polymorphic_detail::serialize_wrapper(Archive&, std::shared_ptr<_Tp2>&, uint32_t) [with Archive = cereal::XMLInputArchive; T = Concept]’
/usr/local/include/cereal/types/polymorphic.hpp:253:5: [ skipping 16 instantiation contexts ]
/usr/include/c++/4.7/bits/shared_ptr_base.h:525:8: required from ‘std::__shared_count<_Lp>::__shared_count(std::_Sp_make_shared_tag, _Tp*, const _Alloc&, _Args&& ...) [with _Tp = SemanticGraph<Concept>; _Alloc = std::allocator<SemanticGraph<Concept> >; _Args = {const char (&)[16]}; __gnu_cxx::_Lock_policy _Lp = (__gnu_cxx::_Lock_policy)2u]’
/usr/include/c++/4.7/bits/shared_ptr_base.h:997:35: required from ‘std::__shared_ptr<_Tp, _Lp>::__shared_ptr(std::_Sp_make_shared_tag, const _Alloc&, _Args&& ...) [with _Alloc = std::allocator<SemanticGraph<Concept> >; _Args = {const char (&)[16]}; _Tp = SemanticGraph<Concept>; __gnu_cxx::_Lock_policy _Lp = (__gnu_cxx::_Lock_policy)2u]’
/usr/include/c++/4.7/bits/shared_ptr.h:317:64: required from ‘std::shared_ptr<_Tp>::shared_ptr(std::_Sp_make_shared_tag, const _Alloc&, _Args&& ...) [with _Alloc = std::allocator<SemanticGraph<Concept> >; _Args = {const char (&)[16]}; _Tp = SemanticGraph<Concept>]’
/usr/include/c++/4.7/bits/shared_ptr.h:599:39: required from ‘std::shared_ptr<_Tp1> std::allocate_shared(const _Alloc&, _Args&& ...) [with _Tp = SemanticGraph<Concept>; _Alloc = std::allocator<SemanticGraph<Concept> >; _Args = {const char (&)[16]}]’
/usr/include/c++/4.7/bits/shared_ptr.h:615:42: required from ‘std::shared_ptr<_Tp1> std::make_shared(_Args&& ...) [with _Tp = SemanticGraph<Concept>; _Args = {const char (&)[16]}]’
/home/alex/projects/Icarus/trunk/Api/ConnectionHandler/../../Processes/Controller/../../Datatypes/Domain/../../Handlers/SemanticNodeFactory/SemanticNodeFactory.hpp:34:82: required from here
/home/alex/projects/Icarus/trunk/Api/ConnectionHandler/../../Processes/Controller/../../Datatypes/Domain/../Episode/../State/../ConceptGraph/../Concept/Concept.hpp:27:5: error: ‘Concept::Concept()’ is private

有人可以向我解释为什么会发生这种情况，更重要的是，除了将这些构造函数公开之外，如何解决它？

编辑：

原始错误行来自：

1	concept_map = std::make_shared<SemanticGraph<Concept>>("concept_map.xml" );

SemanticGraph Ctor在哪里：

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SemanticGraph
(
const std::string filename
)
:
_fname ( filename )
{
std::ifstream input( _fname );
if ( input.is_open() )
{
cereal::XMLInputArchive archive( input );
archive( _nodes );
}
}