GNU hello代码分析

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);
}