misc/dirname.c

   1 /* dirname - return directory part of PATH.
   2    Copyright (C) 1996-2024 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #include <libgen.h>
  20 #include <string.h>
  21
  22
  23 char *
  24 dirname (char *path)
  25 {
  26   static const char dot[] = ".";
  27   char *last_slash;
  28
  29   /* Find last '/'.  */
  30   last_slash = path != NULL ? strrchr (path, '/') : NULL;
  31
  32   if (last_slash != NULL && last_slash != path && last_slash[1] == '\0')
  33     {
  34       /* Determine whether all remaining characters are slashes.  */
  35       char *runp;
  36
  37       for (runp = last_slash; runp != path; --runp)
  38         if (runp[-1] != '/')
  39           break;
  40
  41       /* The '/' is the last character, we have to look further.  */
  42       if (runp != path)
  43         last_slash = __memrchr (path, '/', runp - path);
  44     }
  45
  46   if (last_slash != NULL)
  47     {
  48       /* Determine whether all remaining characters are slashes.  */
  49       char *runp;
  50
  51       for (runp = last_slash; runp != path; --runp)
  52         if (runp[-1] != '/')
  53           break;
  54
  55       /* Terminate the path.  */
  56       if (runp == path)
  57         {
  58           /* The last slash is the first character in the string.  We have to
  59              return "/".  As a special case we have to return "//" if there
  60              are exactly two slashes at the beginning of the string.  See
  61              XBD 4.10 Path Name Resolution for more information.  */
  62           if (last_slash == path + 1)
  63             ++last_slash;
  64           else
  65             last_slash = path + 1;
  66         }
  67       else
  68         last_slash = runp;
  69
  70       last_slash[0] = '\0';
  71     }
  72   else
  73     /* This assignment is ill-designed but the XPG specs require to
  74        return a string containing "." in any case no directory part is
  75        found and so a static and constant string is required.  */
  76     path = (char *) dot;
  77
  78   return path;
  79 }