Extern 的问题 && error LNK2001: unresolved external symbol "class WTL::CAppModule _Module" (?_Module@@3VCAppModule@WTL@@A)

, luther baker <lutherbaker@...> wrote:

> I am walking through this tutorial in visual studio 2008

> http://www.codeproject.com/KB/wtl/wtl4mfc2.aspx


> I am about half way down and per the tutorial, I have implemented

stdafx.h, main.cpp and MyWindow.h. When I try to build this for the

first time, I am receiving:

> error LNK2001: unresolved external symbol "class WTL::CAppModule

_Module" (?_Module@@3VCAppModule@WTL@@A)

>C:/home/lbaker/dev/vstudio/real-estate-czar/vs2008/Debug/real-

estate-czar.exe : fatal error LNK1120: 1 unresolved externals

> I most definitely have this line in my stdafx.h file:

> extern CAppModule _Module;

> But I'm not sure where this gets resolved and I'm having trouble

drilling down to find it.

> Does anyone have some suggestions?

 Thanks,

> -Luther

Defining an "extern" will only make the variable visible across the

source files. You still have to define "CAppModule _Module;"

somewhere in your source code .cpp file. If you are working on

Project.exe, Project.cpp would be a perfect place to define it.

Best regards,

He Shiming



附：http://www.cnblogs.com/luliang/archive/2008/08/21/1272746.html（extern的用法链接）

      http://www.cppblog.com/Macaulish/archive/2008/06/17/53689.html（extern"C"的深入分析）

      http://www.cnblogs.com/skynet/archive/2010/07/10/1774964.html（C++项目中的extern "C" {}）