记得以前学汇编和PE文件的时候知道，系统不会直接调用我们编写的main，而是调用指定的入口地址。实际上这个入口地址，是在链接时候指定的，MS C/C++中使用链接命令/entry:function可以修改默认设置。
那么，默认情况下，我们使用VC编写的应用程序使用的是什么入口函数了？
| 函数 | 默认 |
| mainCRTStartup (or wmainCRTStartup) | An application using /SUBSYSTEM:CONSOLE; calls main (or wmain) |
| WinMainCRTStartup (or wWinMainCRTStartup) | An application using /SUBSYSTEM:WINDOWS; calls WinMain (or wWinMain), which must be defined with __stdcall |
注意，区分入口函数和主函数（main，WinMain）。
默认情况下，控制台程序使用mainCRTStartup作为入口函数，窗口程序使用WinMainCRTStartup作为入口函数。同时，这两个函数都有对应的Unicode版本（前缀加w)。
现在要考虑的是，这些启动函数都做了什么事情？
在vs2008中的crtexe.c文件中可以找到这几个启动函数的定义，如下：
#ifdef _WINMAIN_
#ifdef WPRFLAG
int wWinMainCRTStartup(
#else /* WPRFLAG */
int WinMainCRTStartup(
#endif /* WPRFLAG */
#else /* _WINMAIN_ */
#ifdef WPRFLAG
int wmainCRTStartup(
#else /* WPRFLAG */
int mainCRTStartup(
#endif /* WPRFLAG */
#endif /* _WINMAIN_ */
void
)
{
/*
* The /GS security cookie must be initialized before any exception
* handling targetting the current image is registered. No function
* using exception handling can be called in the current image until
* after __security_init_cookie has been called.
*/
__security_init_cookie();
return __tmainCRTStartup();
}
__declspec(noinline)
int
__tmainCRTStartup(
void
)
{
#ifdef _WINMAIN_
_TUCHAR *lpszCommandLine;
STARTUPINFO StartupInfo;
BOOL inDoubleQuote=FALSE;
__try {
/*
Note: MSDN specifically notes that GetStartupInfo returns no error, and throws unspecified SEH if it fails, so
the very general exception handler below is appropriate
*/
GetStartupInfo( &StartupInfo );
} __except(EXCEPTION_EXECUTE_HANDLER) {
return 255;
}
#endif /* _WINMAIN_ */
/*
* Guard the initialization code and the call to user's main, or
* WinMain, function in a __try/__except statement.
*/
__try
{
/*
* There is a possiblity that the module where this object is
* linked into is a mixed module. In all the cases we gurantee that
* native initialization will occur before managed initialization.
* Also in anycase this code should never be called when some other
* code is initializing native code, that's why we exit in that case.
*
* Do runtime startup initializers.
*
* Note: the only possible entry we'll be executing here is for
* __lconv_init, pulled in from charmax.obj only if the EXE was
* compiled with -J. All other .CRT$XI* initializers are only
* run as part of the CRT itself, and so for the CRT DLL model
* are not found in the EXE. For that reason, we call _initterm,
* not _initterm_e, because __lconv_init will never return failure,
* and _initterm_e is not exported from the CRT DLL.
*
* Note further that, when using the CRT DLL, executing the
* .CRT$XI* initializers is only done for an EXE, not for a DLL
* using the CRT DLL. That is to make sure the -J setting for
* the EXE is not overriden by that of any DLL.
*/
void *lock_free=0;
void *fiberid=((PNT_TIB)NtCurrentTeb())->StackBase;
int nested=FALSE;
while((lock_free=InterlockedCompareExchangePointer((volatile PVOID *)&__native_startup_lock, fiberid, 0))!=0)
{
if(lock_free==fiberid)
{
nested=TRUE;
break;
}
/* some other thread is running native startup/shutdown during a cctor/domain unload.
Should only happen if this DLL was built using the Everett-compat loader lock fix in vcclrit.h
*/
/* wait for the other thread to complete init before we return */
Sleep(1000);
}
if (__native_startup_state == __initializing)
{
_amsg_exit( _RT_CRT_INIT_CONFLICT);
}
else if (__native_startup_state == __uninitialized)
{
__native_startup_state = __initializing;
#ifndef _SYSCRT
if (_initterm_e( __xi_a, __xi_z ) != 0)
{
return 255;
}
#else /* _SYSCRT */
_initterm((_PVFV *)(void *)__xi_a, (_PVFV *)(void *)__xi_z);
#endif /* _SYSCRT */
}
else
{
has_cctor = 1;
}
/*
* do C++ constructors (initializers) specific to this EXE
*/
if (__native_startup_state == __initializing)
{
_initterm( __xc_a, __xc_z );
__native_startup_state = __initialized;
}
_ASSERTE(__native_startup_state == __initialized);
if(!nested)
{
/* For X86, the definition of InterlockedExchangePointer wrongly causes warning C4312 */
#pragma warning(push)
#pragma warning(disable:4312)
InterlockedExchangePointer((volatile PVOID *)&__native_startup_lock, 0);
#pragma warning(pop)
}
/*
* If we have any dynamically initialized __declspec(thread)
* variables, then invoke their initialization for the primary
* thread used to start the process, by calling __dyn_tls_init
* through a callback defined in tlsdyn.obj.
*/
if (__dyn_tls_init_callback != NULL &&
_IsNonwritableInCurrentImage((PBYTE)&__dyn_tls_init_callback))
{
__dyn_tls_init_callback(NULL, DLL_THREAD_ATTACH, NULL);
}
/* Enable buffer count checking if linking against static lib */
_CrtSetCheckCount(TRUE);
#ifdef _WINMAIN_
/*
* Skip past program name (first token in command line).
* Check for and handle quoted program name.
*/
#ifdef WPRFLAG
/* OS may not support "W" flavors */
if (_wcmdln == NULL)
return 255;
lpszCommandLine = (wchar_t *)_wcmdln;
#else /* WPRFLAG */
lpszCommandLine = (unsigned char *)_acmdln;
#endif /* WPRFLAG */
while (*lpszCommandLine > SPACECHAR ||
(*lpszCommandLine&&inDoubleQuote)) {
/*
* Flip the count from 1 to 0 or 0 to 1 if current character
* is DOUBLEQUOTE
*/
if (*lpszCommandLine==DQUOTECHAR) inDoubleQuote=!inDoubleQuote;
#ifdef _MBCS
if (_ismbblead(*lpszCommandLine)) {
if (lpszCommandLine) {
lpszCommandLine++;
}
}
#endif /* _MBCS */
++lpszCommandLine;
}
/*
* Skip past any white space preceeding the second token.
*/
while (*lpszCommandLine && (*lpszCommandLine <= SPACECHAR)) {
lpszCommandLine++;
}
#ifdef WPRFLAG
mainret = wWinMain(
#else /* WPRFLAG */
mainret = WinMain(
#endif /* WPRFLAG */
(HINSTANCE)&__ImageBase,
NULL,
lpszCommandLine,
StartupInfo.dwFlags & STARTF_USESHOWWINDOW
? StartupInfo.wShowWindow
: SW_SHOWDEFAULT
);
#else /* _WINMAIN_ */
#ifdef WPRFLAG
__winitenv = envp;
mainret = wmain(argc, argv, envp);
#else /* WPRFLAG */
__initenv = envp;
mainret = main(argc, argv, envp);
#endif /* WPRFLAG */
#endif /* _WINMAIN_ */
/*
* Note that if the exe is managed app, we don't really need to
* call exit or _c_exit. .cctor should be able to take care of
* this.
*/
if ( !managedapp )
exit(mainret);
if (has_cctor == 0)
_cexit();
}
__except ( _XcptFilter(GetExceptionCode(), GetExceptionInformation()) )
{
/*
* Should never reach here
*/
mainret = GetExceptionCode();
/*
* Note that if the exe is managed app, we don't really need to
* call exit or _c_exit. .cctor should be able to take care of
* this.
*/
if ( !managedapp )
_exit(mainret);
if (has_cctor == 0)
_cexit();
} /* end of try - except */
return mainret;
}