lib/nextelem.c

   1 /* Return the next element of a path.
   2    Copyright (C) 1992 Free Software Foundation, Inc.
   3
   4    This program is free software; you can redistribute it and/or modify
   5    it under the terms of the GNU General Public License as published by
   6    the Free Software Foundation; either version 2, or (at your option)
   7    any later version.
   8
   9    This program 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 General Public License for more details.
  13
  14    You should have received a copy of the GNU General Public License
  15    along with this program; if not, write to the Free Software
  16    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307,
  17    USA.
  18 */
  19
  20 /* Written by David MacKenzie <djm@gnu.ai.mit.edu>,
  21    inspired by John P. Rouillard <rouilj@cs.umb.edu>.  */
  22
  23 #ifdef HAVE_CONFIG_H
  24 #include <config.h>
  25 #endif
  26
  27 #include <stdio.h>
  28 #if defined(HAVE_STRING_H) || defined(STDC_HEADERS)
  29 #include <string.h>
  30 #else
  31 #include <strings.h>
  32 #ifndef strchr
  33 #define strchr index
  34 #endif
  35 #endif
  36 #if defined(STDC_HEADERS)
  37 #include <stdlib.h>
  38 #endif
  39
  40 /* Return the next element of a colon-separated path.
  41    A null entry in the path is equivalent to "." (the current directory).
  42
  43    If NEW_PATH is non-NULL, set the path and return NULL.
  44    If NEW_PATH is NULL, return the next item in the string, or
  45    return NULL if there are no more elements.  */
  46
  47 char *
  48 next_element (char *new_path, int curdir_ok)
  49 {
  50   static char *path = NULL;     /* Freshly allocated copy of NEW_PATH.  */
  51   static char *end;             /* Start of next element to return.  */
  52   static int final_colon;       /* If zero, path didn't end with a colon.  */
  53   char *start;                  /* Start of path element to return.  */
  54
  55   if (new_path)
  56     {
  57       if (path)
  58         free (path);
  59       end = path = strdup (new_path);
  60       final_colon = 0;
  61       return NULL;
  62     }
  63
  64   if (*end == '\0')
  65     {
  66       if (final_colon)
  67         {
  68           final_colon = 0;
  69           return curdir_ok ? "." : NULL;
  70         }
  71       return NULL;
  72     }
  73
  74   start = end;
  75   final_colon = 1;              /* Maybe there will be one.  */
  76
  77   end = strchr (start, ':');
  78   if (end == start)
  79     {
  80       /* An empty path element.  */
  81       *end++ = '\0';
  82       return curdir_ok ? "." : NULL;
  83     }
  84   else if (end == NULL)
  85     {
  86       /* The last path element.  */
  87       end = strchr (start, '\0');
  88       final_colon = 0;
  89     }
  90   else
  91     *end++ = '\0';
  92
  93   return start;
  94 }
  95
  96 #ifdef TEST
  97 int
  98 main ()
  99 {
 100   char *p;
 101
 102   next_element (getenv ("PATH"));
 103   while (p = next_element (NULL))
 104     puts (p);
 105   exit (0);
 106 }
 107 #endif /* TEST */