LIBCMT.LIB(crt0.obj) : error LNK2001: unresolved external symbol _main错误的解决

最近写一个ATL的项目，最终realease的时候出现了这个问题，当时吓了一跳，后来发现了问题，代码没有错误是配置搞错了，因为debug没有任何问题。
出错原因：使用了CRT函数，这些函数需要CRT启动代码，就会出现这种链接错误。因为Release配置的Preprocessor definitions中定义了_ATL_MIN_CRT，它把将CRT启动代码从Dll中删除了。
最简单的办法就是工程设置中删除_ATL_MIN_CRT,但是这样以来就会增加编译后文件的大小。或者工程设置的ignore libraries中输入Libcmt.lib。再次链接时，到几个“unresolved external”的错误，然后你就开始Look for things that you think may be pulling in the startup code and remove them if you can.Instead, use their Win32 equivalents. For example, use lstrcmp() instead of strcmp(). Known functions that require CRT startup code are some of the string and floating point functions.
看了看微软的文档
ATL支持把一个服务器编连优化成最小尺寸或者依赖性最小。我们可以定义三个预处理器符号来影响服务器的优化。
_ATL_MIN_CRT             服务器不链接标准的C/C++运行库
_ATL_DLL                  服务器动态链接工具函数库atl.dll
_ATL_STATIC_REGISTRY    服务器静态链接对组件注册的支持

如果定义了预处理器符号_ATL_MIN_CRT，将不链接C/C++运行库，并且ATL提供了函数malloc、realloc、new和delete的一个实现。当定义了这个符号时，不能调用任何其他的C/C++运行库的函数。
ATL向导生成的ATL工程为所有的Release版本的编连定义了_ATL_MIN_CRT，但是没有为Debug版本定义这个符号。
Debug配置没有定义这三个符号中的任何一个。
RelMinSize配置定义了_ATL_MIN_CRT和_ATL_DLL。
RelMinDependency配置定义了_ATL_MIN_CRT和_ATL_STATIC_REGISTRY。
隐约记得，VC的sp6确实解决了这个bug，还是我比较懒，没有给vc打servicepack6。发现  打开stdafx.cpp，注释掉#include <atlimpl.cpp>也是可以的。
msdn描述
INFO:   LNK2001   Error   ATL   Release   Build  
  ID:   Q165076    
   
   
   
  --------------------------------------------------------------------------------  
  The   information   in   this   article   applies   to:  
   
  Microsoft   Active   Template   Library,   versions   2.0,   2.1,   3.0  
   
  --------------------------------------------------------------------------------  
   
   
  SUMMARY  
  Microsoft   Active   Template   Library   COM   AppWizard   generates   a   release   build   of   your   project   using   macro   _ATL_MIN_CRT.   Selecting   this   configuration   causes   the   C   run-time   (CRT)   library   startup   code   to   not   be   linked   into   your   project.   If   you   use   functions   or   code   in   your   project   that   require   the   use   of   the   C   run-time   library   startup   code,   you   may   experience   LNK2001   -   unresolved   external   errors   when   you   try   to   build   the   release   version   of   your   project.    
   
   
   
  MORE   INFORMATION  
  You   can   use   some   C   run-time   functions   without   requiring   the   CRT   startup   code.   Examples   include   the   mem*   functions.   Other   functions   require   the   CRT   startup   code.   CRT   string   comparisons   for   example   require   the   startup   code   as   the   CRT   initializes   some   tables   used   for   comparing.   Global   objects   that   have   constructors   also   require   the   startup   code.   In   Visual   C++   5.0,   statically   linking   the   startup   code   adds   about   25K   to   your   image   (in   Visual   C++   4.2   it   is   about   20K).    
   
  Following   are   some   suggestions   for   finding   the   cause   of   the   LNK2001   errors:    
   
  In   the   linker   options   there   is   an   "ignore   libraries"   edit   box.   Enter   Libcmt.lib   into   it,   and   build.   You   get   several   unresolved   externals.   This   list   is   everything   that   you   are   using   from   the   CRT.   Look   for   things   that   you   think   may   be   pulling   in   the   startup   code   and   remove   them   if   you   can.    
   
   
  Don't   ignore   Libcmt.lib,   but   turn   on   the   verbose   flag   for   the   linker.   From   this,   you   can   see   what   is   triggering   CRT   startup   code   to   get   pulled   in.    
   
   
  If   you   decide   that   you   really   need   the   startup   code,   then   remove   the   _ATL_MIN_CRT   define   from   the   project   settings.   You   can   also   dynamically   link   to   the   CRT,   which   reduces   your   image   size   but   requires   the   CRT's   DLL.   If   you   turn   on   exception   handling   you   have   to   pull   in   the   startup   code.   Even   when   building   minsize   the   default   is   to   statically   link   to   the   CRT   and   use   _ATL_MIN_CRT.