lib/concat-filename.c

   1 /* Construct a full filename from a directory and a relative filename.
   2    Copyright (C) 2001-2004, 2006-2025 Free Software Foundation, Inc.
   3
   4    This file is free software: you can redistribute it and/or modify
   5    it under the terms of the GNU Lesser General Public License as
   6    published by the Free Software Foundation; either version 2.1 of the
   7    License, or (at your option) any later version.
   8
   9    This file 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
  12    GNU Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public License
  15    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  16
  17 /* Written by Bruno Haible <haible@clisp.cons.org>.  */
  18
  19 #include <config.h>
  20
  21 /* Specification.  */
  22 #include "concat-filename.h"
  23
  24 #include <errno.h>
  25 #include <stdlib.h>
  26 #include <string.h>
  27
  28 #include "filename.h"
  29
  30 /* Concatenate a directory filename, a relative filename and an optional
  31    suffix.  The directory may end with the directory separator.  The second
  32    argument may not start with the directory separator (it is relative).
  33    Return a freshly allocated filename.  Return NULL and set errno
  34    upon memory allocation failure.  */
  35 char *
  36 concatenated_filename (const char *directory, const char *filename,
  37                        const char *suffix)
  38 {
  39   char *result;
  40   char *p;
  41
  42   if (strcmp (directory, ".") == 0)
  43     {
  44       /* No need to prepend the directory.  */
  45       result = (char *) malloc (strlen (filename)
  46                                 + (suffix != NULL ? strlen (suffix) : 0)
  47                                 + 1);
  48       if (result == NULL)
  49         return NULL; /* errno is set here */
  50       p = result;
  51     }
  52   else
  53     {
  54       size_t directory_len = strlen (directory);
  55       int need_slash =
  56         (directory_len > FILE_SYSTEM_PREFIX_LEN (directory)
  57          && !ISSLASH (directory[directory_len - 1]));
  58       result = (char *) malloc (directory_len + need_slash
  59                                 + strlen (filename)
  60                                 + (suffix != NULL ? strlen (suffix) : 0)
  61                                 + 1);
  62       if (result == NULL)
  63         return NULL; /* errno is set here */
  64       memcpy (result, directory, directory_len);
  65       p = result + directory_len;
  66       if (need_slash)
  67         *p++ = '/';
  68     }
  69   p = stpcpy (p, filename);
  70   if (suffix != NULL)
  71     stpcpy (p, suffix);
  72   return result;
  73 }