c++工厂模式使用模板进行自注册

我的问题对应于约翰内斯的回答是否有一种方法从持有其类名的字符串实例化对象?以及斯宾塞·罗斯最近的评论因为我不能在这里添加评论，所以我决定开始一个新问题。

约翰的建议正是我所需要的。我以完全相同的方式实现了它，但我使用VS2008有一个未解决的外部符号链接器错误，这似乎与地图有关。这几天我一直在努力解决这个问题。今天我读了斯宾塞的评论，加上了他建议的那行

BaseFactory::map_type BaseFactory::map = new map_type();

到Base.hpp。现在我得到一个LNK2005错误

Derivedb.obj : error LNK2005:
"private: static class std::map<class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >,class Base * (__cdecl*)(void),struct std::less<class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > >,class std::allocator<struct std::pair<class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > const ,class Base * (__cdecl*)(void)> > > * BaseFactory::map"
(?map@BaseFactory@@0PAV?$map@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@P6APAVBase@@XZU?$less@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@2@V?$allocator@U?$pair@$$CBV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@P6APAVBaser@@XZ@std@@@2@@std@@A)
already defined in Switcher.obj
Project.exe : fatal error LNK1169: one or more multiply defined symbols found) 

代替LNK2001错误

(Switcher.obj : error LNK2001: unresolved external symbol "private: static class std::map<class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >,class Base * (__cdecl*)(void),struct std::less<class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > >,class std::allocator<struct std::pair<class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > const ,class Base * (__cdecl*)(void)> > > * BaseFactory::map" (?map@BaseFactory@@0PAV?$map@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@P6APAVBase@@XZU?$less@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@2@V?$allocator@U?$pair@$$CBV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@P6APAVBase@@XZ@std@@@2@@std@@A)
1>Derivedb.obj : error LNK2001: unresolved external symbol "private: static class std::map<class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >,class Base * (__cdecl*)(void),struct std::less<class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > >,class std::allocator<struct std::pair<class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > const ,class Base * (__cdecl*)(void)> > > * BaseFactory::map" (?map@BaseFactory@@0PAV?$map@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@P6APAVBase@@XZU?$less@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@2@V?$allocator@U?$pair@$$CBV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@P6APAVBase@@XZ@std@@@2@@std@@A)
1>Project.exe : fatal error LNK1120: 1 unresolved externals)

意味着我可能已经定义了它两次??请斯宾塞或有人张贴改进的基础。hpp代码。这是一个非常重要的解决方案，它肯定会对更多的c++编程新手有所帮助。

第二个问题:——>这个问题解决了!谢谢!

我需要在base.hpp中的一些函数声明。这些应该在基类中抽象，并在子类中实现(例如Derivedb.cpp)。但

public:
       virtual ReadInFile(std::string path, std::string filename) = 0;

base.hpp中的

出现编译错误。移除"= 0"解决了编译器错误。但现在我有另一个无法解决的外部符号LNK2001错误

Derivedb.obj: error LNK2001: unresolved external symbol
"public: virtual __thiscall Base::ReadInFile(class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >,class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >)"
(?ReadInFile@Base@@UAE_NPAV@@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@1@Z).

在另一个cpp文件

中调用

Base* importer =  BaseFactory::createInstance("DerivedB");
importer->ReadInFile(m_path, m_filename);

也许是不清楚哪个函数(基或子类)需要被调用，因为它不是抽象的基类?有办法解决这个问题吗?谢谢你！

class BaseFactory
{
private:
    static int map;
};

int BaseFactory::map = 392;