c-function changes without checking out source code

Hi, 
I am trying to get the c-function changes between two cvs versions without checking out the source.  Currently ifI have the source checked out, this command does the job: cvs -d base:root diff -p -u -r1 -r2 path.

However if I don't have the code checked out, I get: cvs [diff aborted]: no such directory `path' 

rdiff shows the changes without checking out the code but then there is no -p option to display the c-functions changes. Are there any suggestions to get the c-function changes without  checking out the code?

Thanks
Venkat