I have noticed following problem. It's OK to run all *.c like
"ruby ..\ruby\bin\rdoc ..\ruby\*.c -d -o \temp".

E:\ruby-cvs\win32>ruby ..\ruby\bin\rdoc ..\ruby\dir.c -d -o \temp

                              dir.c: c..........................
Generating HTML...
Diagrams: E:/ruby-cvs/ruby/lib/rdoc/diagram.rb:187:in `add_classes': undefined m
ethod `file_relative_name' for nil:NilClass (NoMethodError)
        from E:/ruby-cvs/ruby/lib/rdoc/generators/html_generator.rb:1205:in `eac
h_with_index'
        from E:/ruby-cvs/ruby/lib/rdoc/diagram.rb:186:in `add_classes'
        from E:/ruby-cvs/ruby/lib/rdoc/diagram.rb:74:in `draw'
        from E:/ruby-cvs/ruby/lib/rdoc/generators/html_generator.rb:1205:in `eac
h_with_index'
        from E:/ruby-cvs/ruby/lib/rdoc/diagram.rb:53:in `draw'
        from E:/ruby-cvs/ruby/lib/rdoc/rdoc.rb:262:in `document'
        from ../ruby/bin/rdoc:63

Date: 2008-09-22 06:21
Sender: Designing Patterns

I think that this is fixed in RDoc 2.2; RDoc now is smart enough
to handle encountering a method for a class before encountering
the class definition.

Date: 2006-03-01 09:46
Sender: Hirokazu Yamamoto

This happens because File's method is defined in dir.c.

    rb_define_singleton_method(rb_cFile,"fnmatch",
file_s_fnmatch, -1);
    rb_define_singleton_method(rb_cFile,"fnmatch?",
file_s_fnmatch, -1);