1  /* dirname.c -- return all but the last element in a file name
       2  
       3     Copyright (C) 1990, 1998, 2000-2001, 2003-2006, 2009-2023 Free Software
       4     Foundation, Inc.
       5  
       6     This file is free software: you can redistribute it and/or modify
       7     it under the terms of the GNU Lesser General Public License as
       8     published by the Free Software Foundation; either version 2.1 of the
       9     License, or (at your option) any later version.
      10  
      11     This file 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
      14     GNU Lesser General Public License for more details.
      15  
      16     You should have received a copy of the GNU Lesser General Public License
      17     along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
      18  
      19  #include <config.h>
      20  
      21  #include "dirname.h"
      22  
      23  #include <stdlib.h>
      24  #include <string.h>
      25  
      26  /* Return the length of the prefix of FILE that will be used by
      27     dir_name.  If FILE is in the working directory, this returns zero
      28     even though 'dir_name (FILE)' will return ".".  Works properly even
      29     if there are trailing slashes (by effectively ignoring them).  */
      30  
      31  size_t
      32  dir_len (char const *file)
      33  {
      34    size_t prefix_length = FILE_SYSTEM_PREFIX_LEN (file);
      35    size_t length;
      36  
      37    /* Advance prefix_length beyond important leading slashes.  */
      38    prefix_length += (prefix_length != 0
      39                      ? (FILE_SYSTEM_DRIVE_PREFIX_CAN_BE_RELATIVE
      40                         && ISSLASH (file[prefix_length]))
      41                      : (ISSLASH (file[0])
      42                         ? ((DOUBLE_SLASH_IS_DISTINCT_ROOT
      43                             && ISSLASH (file[1]) && ! ISSLASH (file[2])
      44                             ? 2 : 1))
      45                         : 0));
      46  
      47    /* Strip the basename and any redundant slashes before it.  */
      48    for (length = last_component (file) - file;
      49         prefix_length < length; length--)
      50      if (! ISSLASH (file[length - 1]))
      51        break;
      52    return length;
      53  }
      54  
      55  
      56  /* In general, we can't use the builtin 'dirname' function if available,
      57     since it has different meanings in different environments.
      58     In some environments the builtin 'dirname' modifies its argument.
      59  
      60     Return the leading directories part of FILE, allocated with malloc.
      61     Works properly even if there are trailing slashes (by effectively
      62     ignoring them).  Return NULL on failure.
      63  
      64     If lstat (FILE) would succeed, then { chdir (dir_name (FILE));
      65     lstat (base_name (FILE)); } will access the same file.  Likewise,
      66     if the sequence { chdir (dir_name (FILE));
      67     rename (base_name (FILE), "foo"); } succeeds, you have renamed FILE
      68     to "foo" in the same directory FILE was in.  */
      69  
      70  char *
      71  mdir_name (char const *file)
      72  {
      73    size_t length = dir_len (file);
      74    bool append_dot = (length == 0
      75                       || (FILE_SYSTEM_DRIVE_PREFIX_CAN_BE_RELATIVE
      76                           && length == FILE_SYSTEM_PREFIX_LEN (file)
      77                           && file[2] != '\0' && ! ISSLASH (file[2])));
      78    char *dir = malloc (length + append_dot + 1);
      79    if (!dir)
      80      return NULL;
      81    memcpy (dir, file, length);
      82    if (append_dot)
      83      dir[length++] = '.';
      84    dir[length] = '\0';
      85    return dir;
      86  }