-/* Return the leading directories part of PATH,
- allocated with malloc. If out of memory, return 0.
- Assumes that trailing slashes have already been
- removed. */
+ /* Advance prefix_length beyond important leading slashes. */
+ prefix_length += (prefix_length != 0
+ ? (FILE_SYSTEM_DRIVE_PREFIX_CAN_BE_RELATIVE
+ && ISSLASH (file[prefix_length]))
+ : (ISSLASH (file[0])
+ ? ((DOUBLE_SLASH_IS_DISTINCT_ROOT
+ && ISSLASH (file[1]) && ! ISSLASH (file[2])
+ ? 2 : 1))
+ : 0));
+
+ /* Strip the basename and any redundant slashes before it. */
+ for (length = last_component (file) - file;
+ prefix_length < length; length--)
+ if (! ISSLASH (file[length - 1]))
+ break;
+ return length;
+}
+
+
+/* In general, we can't use the builtin `dirname' function if available,
+ since it has different meanings in different environments.
+ In some environments the builtin `dirname' modifies its argument.
+
+ Return the leading directories part of FILE, allocated with xmalloc.
+ Works properly even if there are trailing slashes (by effectively
+ ignoring them). Unlike POSIX dirname(), FILE cannot be NULL.
+
+ If lstat (FILE) would succeed, then { chdir (dir_name (FILE));
+ lstat (base_name (FILE)); } will access the same file. Likewise,
+ if the sequence { chdir (dir_name (FILE));
+ rename (base_name (FILE), "foo"); } succeeds, you have renamed FILE
+ to "foo" in the same directory FILE was in. */