编译器链接启动代码crtexe.c

你是否想过为什么有时候main（）函数是入口地址，在win32中winmain()函数又是入口地址，其实是编译器在动态链接到crt[C runtime library(part of the C standard library)]时候设置的

程序设置断点，我们来看crtexe.c代码

第一个static int __cdecl pre_c_init(void)

*       The code in mainCRTStartup that was executed before executing C   initializers was shifted in this function. Also this funciton is the   first thing that is executed in c init section.

什么意思不用详细说，老外的注释很给力

static int __cdecl pre_c_init(void){    /*     * Determine if this is a managed application     */    managedapp = check_managed_app();    /*     * Set __app_type properly     */#ifdef _WINMAIN_    //根据WINMAIN宏来设置应用程序是GUI程序还是控制台程序    __set_app_type(_GUI_APP);#else  /* _WINMAIN_ */    __set_app_type(_CONSOLE_APP);#endif  /* _WINMAIN_ */    /*     * Mark this module as an EXE file so that atexit/_onexit     * will do the right thing when called, including for C++     * d-tors.     */    __onexitbegin = __onexitend = (_PVFV *)_encode_pointer((_PVFV *)(-1));    /*     * Propogate the _fmode and _commode variables to the DLL     */    *_IMP___FMODE = _fmode;    *_IMP___COMMODE = _commode;#ifdef _M_IX86    /*     * Set the local copy of the Pentium FDIV adjustment flag     */    _adjust_fdiv = * _imp___adjust_fdiv;#endif  /* _M_IX86 */    /*     * Run the RTC initialization code for this DLL     */#ifdef _RTC    _RTC_Initialize();#endif  /* _RTC */    /*     * Call _setargv(), which will trigger a call to __setargv() if     * SETARGV.OBJ is linked with the EXE.  If SETARGV.OBJ is not     * linked with the EXE, a dummy _setargv() will be called.     */#ifdef WPRFLAG    _wsetargv();#else  /* WPRFLAG */    _setargv();#endif  /* WPRFLAG */    /*     * If the user has supplied a _matherr routine then set     * __pusermatherr to point to it.     */    if ( !__defaultmatherr )        __setusermatherr(_matherr);#ifdef _M_IX86    _setdefaultprecision();#endif  /* _M_IX86 */    /* Enable per-thread locale if user asked for it */    if(__globallocalestatus == -1)    {        _configthreadlocale(-1);    }    return 0;}

这个函数在crt0dat.c中被调用，详细介绍，略去

第二个函数

static void __cdecl pre_cpp_init(void)

static void __cdecl pre_cpp_init(void){#ifdef _RTC    atexit(_RTC_Terminate);  //注册程序退出时的清理工#endif  /* _RTC */    /*     * Get the arguments for the call to main. Note this must be     * done explicitly, rather than as part of the dll's     * initialization, to implement optional expansion of wild     * card chars in filename args     */    startinfo.newmode = _newmode;#ifdef WPRFLAG    argret = __wgetmainargs(&argc, &argv, &envp,                            _dowildcard, &startinfo);#else  /* WPRFLAG */    argret = __getmainargs(&argc, &argv, &envp,                           _dowildcard, &startinfo);#endif  /* WPRFLAG */#ifndef _SYSCRT    if (argret < 0)        _amsg_exit(_RT_SPACEARG);#endif  /* _SYSCRT */}

下面是程序的第一个入口处

staticint__tmainCRTStartup(         void         );#ifdef _WINMAIN_#ifdef WPRFLAGint wWinMainCRTStartup(#else  /* WPRFLAG */int WinMainCRTStartup(#endif  /* WPRFLAG */#else  /* _WINMAIN_ */#ifdef WPRFLAGint 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();}

/***
*mainCRTStartup(void)
*wmainCRTStartup(void)
*WinMainCRTStartup(void)
*wWinMainCRTStartup(void)
*
*Purpose:
*       These routines do the C runtime initialization, call the appropriate
*       user entry function, and handle termination cleanup.  For a managed
*       app, they then return the exit code back to the calling routine, which
*       is the managed startup code.  For an unmanaged app, they call exit and
*       never return.
*
*       Function:               User entry called:
*       mainCRTStartup          main
*       wmainCRTStartup         wmain
*       WinMainCRTStartup       WinMain
*       wWinMainCRTStartup      wWinMain
就是为程序找到入口地址，具体的判断是在函数__tmainCRTStartup()中

关键代码：

#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_ */

我们看到，根据宏WPRFLAG来判断是wWinmain（）还是WinMain()，根据_WINMAIN_来判断入口函数是main（），wmain（）还是WinMain(),wWinMain()

wmain()和wWinMain(）是unicode版的，main()和WinMain()是ANSI版的 不过在程序中始终没有找到宏WPRFLAG是在哪里定义的，有空了再详细研究

然后就找到对应的入口程序执行。