misc/dirname.c

   1 /* dirname - return directory part of PATH.
   2    Copyright (C) 1996-2017 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4    Contributed by Ulrich Drepper <drepper@cygnus.com>, 1996.
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Lesser General Public
   8    License as published by the Free Software Foundation; either
   9    version 2.1 of the License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library; if not, see
  18    <http://www.gnu.org/licenses/>.  */
  19
  20 #include <libgen.h>
  21 #include <string.h>
  22
  23
  24 char *
  25 dirname (char *path)
  26 {
  27   static const char dot[] = ".";
  28   char *last_slash;
  29
  30   /* Find last '/'.  */
  31   last_slash = path != NULL ? strrchr (path, '/') : NULL;
  32
  33   if (last_slash != NULL && last_slash != path && last_slash[1] == '\0')
  34     {
  35       /* Determine whether all remaining characters are slashes.  */
  36       char *runp;
  37
  38       for (runp = last_slash; runp != path; --runp)
  39         if (runp[-1] != '/')
  40           break;
  41
  42       /* The '/' is the last character, we have to look further.  */
  43       if (runp != path)
  44         last_slash = __memrchr (path, '/', runp - path);
  45     }
  46
  47   if (last_slash != NULL)
  48     {
  49       /* Determine whether all remaining characters are slashes.  */
  50       char *runp;
  51
  52       for (runp = last_slash; runp != path; --runp)
  53         if (runp[-1] != '/')
  54           break;
  55
  56       /* Terminate the path.  */
  57       if (runp == path)
  58         {
  59           /* The last slash is the first character in the string.  We have to
  60              return "/".  As a special case we have to return "//" if there
  61              are exactly two slashes at the beginning of the string.  See
  62              XBD 4.10 Path Name Resolution for more information.  */
  63           if (last_slash == path + 1)
  64             ++last_slash;
  65           else
  66             last_slash = path + 1;
  67         }
  68       else
  69         last_slash = runp;
  70
  71       last_slash[0] = '\0';
  72     }
  73   else
  74     /* This assignment is ill-designed but the XPG specs require to
  75        return a string containing "." in any case no directory part is
  76        found and so a static and constant string is required.  */
  77     path = (char *) dot;
  78
  79   return path;
  80 }