dirname

/*
 *  call-seq:
 *     File.dirname(file_name ) -> dir_name
 *  
 *  Returns all components of the filename given in <i>file_name</i>
 *  except the last one. The filename must be formed using forward
 *  slashes (``<code>/</code>'') regardless of the separator used on the
 *  local file system.
 *     
 *     File.dirname("/home/gumby/work/ruby.rb")   #=> "/home/gumby/work"
 */

static VALUE
rb_file_s_dirname(klass, fname)
    VALUE klass, fname;
{
    const char *name, *root, *p;
    VALUE dirname;

    name = StringValueCStr(fname);
    root = skiproot(name);
#ifdef DOSISH_UNC
    if (root > name + 1 && isdirsep(*name))
        root = skipprefix(name = root - 2);
#else
    if (root > name + 1)
        name = root - 1;
#endif
    p = strrdirsep(root);
    if (!p) {
        p = root;
    }
    if (p == name)
        return rb_str_new2(".");
#ifdef DOSISH_DRIVE_LETTER
    if (has_drive_letter(name) && isdirsep(*(name + 2))) {
        const char *top = skiproot(name + 2);
        dirname = rb_str_new(name, 3);
        rb_str_cat(dirname, top, p - top);
    }
    else
#endif
    dirname = rb_str_new(name, p - name);
#ifdef DOSISH_DRIVE_LETTER
    if (has_drive_letter(name) && root == name + 2 && p - name == 2)
        rb_str_cat(dirname, ".", 1);
#endif
    OBJ_INFECT(dirname, fname);
    return dirname;
}