sysdeps/unix/getlogin.c

   1 /* Copyright (C) 1991, 1992, 1996 Free Software Foundation, Inc.
   2 This file is part of the GNU C Library.
   3
   4 The GNU C Library is free software; you can redistribute it and/or
   5 modify it under the terms of the GNU Library General Public License as
   6 published by the Free Software Foundation; either version 2 of the
   7 License, or (at your option) any later version.
   8
   9 The GNU C Library is distributed in the hope that it will be useful,
  10 but WITHOUT ANY WARRANTY; without even the implied warranty of
  11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12 Library General Public License for more details.
  13
  14 You should have received a copy of the GNU Library General Public
  15 License along with the GNU C Library; see the file COPYING.LIB.  If
  16 not, write to the Free Software Foundation, Inc., 675 Mass Ave,
  17 Cambridge, MA 02139, USA.  */
  18
  19 #include <errno.h>
  20 #include <unistd.h>
  21 #include <string.h>
  22 #include <stdio.h>
  23 #include <limits.h>
  24 #include <fcntl.h>
  25
  26 #include <utmp.h>
  27
  28 /* Return the login name of the user, or NULL if it can't be determined.
  29    The returned pointer, if not NULL, is good only until the next call.  */
  30
  31 char *
  32 getlogin (void)
  33 {
  34   char tty_pathname[2 + 2 * NAME_MAX];
  35   char *real_tty_path = tty_pathname;
  36   char *result = NULL;
  37   struct utmp_data utmp_data = { ut_fd: -1 };
  38   static char name[UT_NAMESIZE + 1];
  39   struct utmp *ut, line;
  40
  41   /* Get name of tty connected to fd 0.  Return NULL if not a tty or
  42      if fd 0 isn't open.  Note that a lot of documentation says that
  43      getlogin() is based on the controlling terminal---what they
  44      really mean is "the terminal connected to standard input".  The
  45      getlogin() implementation of DEC Unix, SunOS, Solaris, HP-UX all
  46      return NULL if fd 0 has been closed, so this is the compatible
  47      thing to do.  Note that ttyname(open("/dev/tty")) on those
  48      systems returns /dev/tty, so that is not a possible solution for
  49      getlogin().  */
  50   if (__ttyname_r (0, real_tty_path, sizeof (tty_pathname)) < 0)
  51     return NULL;
  52
  53   real_tty_path += 5;           /* Remove "/dev/".  */
  54
  55   __setutent_r (&utmp_data);
  56   strncpy (line.ut_line, real_tty_path, sizeof line.ut_line);
  57   if (__getutline_r (&line, &ut, &utmp_data) < 0)
  58     {
  59       if (errno == ESRCH)
  60         /* The caller expects ENOENT if nothing is found.  */
  61         __set_errno (ENOENT);
  62       result = NULL;
  63     }
  64   else
  65     {
  66       strncpy (name, ut->ut_user, UT_NAMESIZE);
  67       name[UT_NAMESIZE] = '\0';
  68       result = name;
  69     }
  70
  71   __endutent_r (&utmp_data);
  72
  73   return result;
  74 }