描述:
我在一个空的ATL com项目中，想使用
#include <string>
#include <fstream>
#include <sstream>
#include <iostream>
这几个头文件中的类，
结果在Debug时，一切OK没有问题，
但我在Release minsize时，就报
Generating Code...
Linking...
Creating library ReleaseMinSize/ATLTest.lib and object ReleaseMinSize/ATLTest.exp
LIBCMT.lib(crt0.obj) : error LNK2001: unresolved external symbol _main
ReleaseMinSize/ATLTest.dll : fatal error LNK1120: 1 unresolved externals
Error executing link.exe.
但我能够包含比如＃include <vector>
这样的stl头文件，但不能使用上面的四个，而且是Debug可以，release不可以。
不知是为什么？
解决方案1:
ATL工程里如果用到了C运行库函数,就不能再用这个宏了.
The following also applies to ATL 3.0:
A. This usually happens when the C Run-Time (CRT) startup code is required for some CRT functions. You can either remove all references to the CRT functions that require the startup code or remove the _ATL_MIN_CRT preprocessor definition from your compiler settings.
You can link statically or dynamically to the CRT. Statically linking causes the CRT code to be placed in your executable image and you do not need to have the CRT DLL (Msvcrt.dll). If you dynamically link to the CRT, references to the code in Msvcrt.dll are placed in your image. For your image to run, Msvcrt.dll must be present. Even when dynamically linking to the CRT, there can still be some code statically linked, such as DllMainCRTStartup.
An entry point, explicitly or implicitly specified when linking, is called by the operating system after loading the image. For a DLL, the default entry point is DllMainCRTStartup. For an EXE, it is WinMainCRTStartup. You can override the default with the /ENTRY linker option. The CRT provides an implementation for DllMainCRTStartup, WinMainCRTStartup, and wWinMainCRTStartup (UNICODE entry point for an EXE). These entry points (CRT startup code) call constructors on global objects and initialize some data structures used by some CRT functions. This startup code adds about 25K to your image when statically linking.
Some CRT functions can be used without the CRT startup code, for example, functions with the mem prefix, wcslen, wcscmp, and strlen. The following require the CRT startup code:
String comparison routines
Memory allocation routines
Global objects with constructors
C++ exception handling (/GX)
ATL is aimed at minimizing the image size and the reliance on run-time DLLs. It provides alternative implementations for common CRT APIs that would otherwise require the CRT startup code. The use of these APIs is controlled by the _ATL_MIN_CRT macro. Using _ATL_MIN_CRT does not mean that you cannot use the CRT routines. However, if you use the routines that require the CRT startup code, then you will get a linker error that _main is unresolved. Providing your own implementation of _main does not solve this problem.
If C++ exceptions (/GX) are enabled, then you must link in the startup code. The _ATL_MIN_CRT macro cannot be used in this case. MFC requires code to be compiled with the /GX option. Therefore, you cannot use _ATL_MIN_CRT in conjunction with MFC. You can use SEH (structured exception handling), __try, and __except with _ATL_MIN_CRT, because the startup code is not required. In many cases, since most of the CRT source code ships with the product, you can use some of this code and replace only parts of it with system calls to avoid the startup code.
To find out what is causing the problem, do one of the following:
Open the Project Settings dialog box, select the Link tab, and click Input in the Category box. Type LIBCMT.LIB in the Ignore libraries text box. Now do a build. You will get a list of unresolved externals. This list contains the CRT routines you are using. Look for the routines that you think may require the startup code.
Turn on the /VERBOSE linker option. From the resulting linker output, you can find a list of routines that require the CRT startup code.
If you need the startup code, then remove the _ATL_MIN_CRT definition from the Project Settings. You can also dynamically link to CRT. This reduces your image size but requires Msvcrt.dll.
When building as Release, the default option is to statically link to CRT and use _ATL_MIN_CRT. This gives a smaller image size than dynamically linking to CRT, at least when the startup code is avoided and the CRT APIs used by AppWizard are used.