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GNU中的一个软件包，包名叫hello，呵呵，看来很简单啦。

今天就来分析一下，GNU的目的是通过这个说明一下，GNU标准软件包所应遵守的规则，以及一些必须的测试，编译脚本文件等。

俺就不分析其他的了，直接上最具价值的代码，其他忽略，这个程序实在是太小了，最重要的是一个getopt_long函数的应用，

用于解析命令行参数的。

#include <config.h> #include "system.h" #include "errno.h" #include "error.h" #include "progname.h" #include "xalloc.h" static const struct option longopts[] = {   {"greeting", required_argument, NULL, 'g'}, 需要参数   {"help", no_argument, NULL, 'h'},   不需要参数   {"traditional", no_argument, NULL, 't'},   {"version", no_argument, NULL, 'v'},   {NULL, 0, NULL, 0}    通过man getopt_long发现，这个结构体需要以NULL结束。 }; /* Forward declarations.  */ 前向声明，估计调用在实现之前。 static void print_help (void); static void print_version (void); int main (int argc, char *argv[])  关键的入口函数在这里啦。 {   int optc;   int lose = 0;   const char *greeting_msg;   wchar_t *mb_greeting;   size_t len;   set_program_name (argv[0]);   /* Set locale via LC_ALL.  */   setlocale (LC_ALL, ""); #if ENABLE_NLS   /* Set the text message domain.  */   bindtextdomain (PACKAGE, LOCALEDIR);   textdomain (PACKAGE); #endif   /* Having initialized gettext, get the default message. */   greeting_msg = _("Hello, world!");  常指针指向一个字符串常量，C语言中有_()这个用法吗？难道是GNU的扩展？？？   /* Even exiting has subtleties.  On exit, if any writes failed, change      the exit status.  The /dev/full device on GNU/Linux can be used for      testing; for instance, hello >/dev/full should exit unsuccessfully.      This is implemented in the Gnulib module "closeout".  */   atexit (close_stdout);   这个函数用于处理命令行参数，字符后面跟一个冒号表示需要一个参数。   该函数返回短命令符，下面的程序通过case判断。   while ((optc = getopt_long (argc, argv, "g:htv", longopts, NULL)) != -1)     switch (optc)       {     /* --help and --version exit immediately, per GNU coding standards.  */       case 'v':     print_version ();     exit (EXIT_SUCCESS);     break;       case 'g':     greeting_msg = optarg; // extern char *optarg;一个全局变量，getopt用它来保存参数     break;       case 'h':     print_help ();     exit (EXIT_SUCCESS);     break;       case 't':     greeting_msg = _("hello, world");     break;       default:     lose = 1;     break;       }   if (lose || optind < argc)     {       /* Print error message and exit.  */       error (0, 0, "%s: %s", _("extra operand"), argv[optind]);       print_help ();     }   len = mbsrtowcs(NULL, &greeting_msg, 0, NULL);   if (len == (size_t)-1)     error (EXIT_FAILURE, errno, _("conversion to a multibyte string failed"));   mb_greeting = xmalloc((len + 1) * sizeof(wchar_t));   mbsrtowcs(mb_greeting, &greeting_msg, len + 1, NULL);   /* Print greeting message and exit. */   wprintf (L"%ls\n", mb_greeting);   free(mb_greeting);   exit (EXIT_SUCCESS); } /* Print help info.  This long message is split into    several pieces to help translators be able to align different    blocks and identify the various pieces.  */ static void print_help (void) {   /* TRANSLATORS: --help output 1 (synopsis)      no-wrap */   printf (_("\ Usage: %s [OPTION]...\n"), program_name);   /* TRANSLATORS: --help output 2 (brief description)      no-wrap */   fputs (_("\ Print a friendly, customizable greeting.\n"), stdout);   puts ("");   /* TRANSLATORS: --help output 3: options 1/2      no-wrap */   fputs (_("\   -h, --help          display this help and exit\n\   -v, --version       display version information and exit\n"), stdout);   puts ("");   /* TRANSLATORS: --help output 4: options 2/2      no-wrap */   fputs (_("\   -t, --traditional       use traditional greeting\n\   -g, --greeting=TEXT     use TEXT as the greeting message\n"), stdout);   printf ("\n");   /* TRANSLATORS: --help output 5+ (reports)      TRANSLATORS: the placeholder indicates the bug-reporting address      for this application.  Please add _another line_ with the      address for translation bugs.      no-wrap */   printf (_("\ Report bugs to: %s\n"), PACKAGE_BUGREPORT); #ifdef PACKAGE_PACKAGER_BUG_REPORTS   printf (_("Report %s bugs to: %s\n"), PACKAGE_PACKAGER,       PACKAGE_PACKAGER_BUG_REPORTS); #endif #ifdef PACKAGE_URL   printf (_("%s home page: <%s>\n"), PACKAGE_NAME, PACKAGE_URL); #else   printf (_("%s home page: <http://www.gnu.org/software/%s/>\n"),       PACKAGE_NAME, PACKAGE); #endif   fputs (_("General help using GNU software: <http://www.gnu.org/gethelp/>\n"),      stdout); } /* Print version and copyright information.  */ static void print_version (void) {   printf ("%s (%s) %s\n", PACKAGE, PACKAGE_NAME, VERSION);   /* xgettext: no-wrap */   puts ("");   /* It is important to separate the year from the rest of the message,      as done here, to avoid having to retranslate the message when a new      year comes around.  */   printf (_("\ Copyright (C) %d Free Software Foundation, Inc.\n\ License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>\n\ This is free software: you are free to change and redistribute it.\n\ There is NO WARRANTY, to the extent permitted by law.\n"), COPYRIGHT_YEAR); }

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