C++期望的主表達式編譯錯誤

Question

#include <boost/format.hpp> 
#include <boost/scoped_ptr.hpp> 
#include <stdexcept> 
#include <unordered_map> 
#include <functional> 
#define DECLARE_OBJECT(classname) namespace {core::declare_object<classname> __declarartion_#classname;} 

namespace core { 
    class dungeon; 
    class object; 
    typedef std::function<object* (dungeon *)> object_creator; 
    namespace library_type { 
    enum type { 
     landscape = 0, walker, foe, bonus,object = 42 
    }; 
    }; 
    struct library_error : public std::logic_error 
    { 
    explicit library_error(const std::string &what) : std::logic_error(what) {}; 
    }; 
    template <enum library_type::type type> 
    class library { 
    public: 
    static library<type> *instance() { 
     if (!m_instance) 
     m_instance = new library<type>(); 
     return m_instance; 
    } 
    template<typename T> 
    void add_object() { 
     boost::scoped_ptr<T> obj(T::create(nullptr)); 
     m_library.insert(obj->name(), T::create); 
    } 
    const object_creator& get_object(const std::string &key) { 
     auto lookup_iterator = m_library.find(key); 
     if (lookup_iterator == m_library.end()) 
     throw library_error(boost::format("Object creator for key `%1%' not found\n") % key); 
     return *lookup_iterator; 
    } 
    private: 
    library() {}; 
    static library<type> *m_instance; 
    std::unordered_map<std::string, object_creator> m_library; 
    }; 
    template <enum library_type::type type> 
    library<type>* library<type>::m_instance; 
    template <enum library_type::type type, typename T> 
    struct declare_object 
    { 
    declare_object() { 
     auto instance = library<type>::instance(); 
     auto method = instance->add_object<T>; 
     method(); 
    } 
    }; 
}; 
int main() 
{ 

} 

你好。這個簡單的C++ 0x代碼給我錯誤declare_object構造

example.cpp: In constructor ‘core::declare_object<type, T>::declare_object()’: 
example.cpp:52:43: error: expected primary-expression before ‘>’ token 
example.cpp:52:44: error: expected primary-expression before ‘;’ token 

我真的不知道我在哪裏錯了。也許清晰的觀點和建議？ 對不起長列表。編輯：答案是auto method = instance -> template add_object<T>;。爲什麼你刪除了你的答案？

Answer 1

要獲得指向成員函數的指針，您需要遵循其他答案中的語法。

由於成員函數是另外一個模板，你需要指出這一點，因爲它是一個從屬名稱：

auto method = &library_type<type>::template add_object<T>; 

否則C++將在add_object<T>解析尖括號爲小於和大於運營商。

Answer 2

struct declare_object 
    { 
    declare_object() { 
     auto instance = library<type>::instance(); 
     auto method = &library<type>::template add_object<T>; 
     (instance->*method)(); 
    } 
    };