diff-save-buffer is a little replacement save-buffer offering a filename in DiffMode based on the parent filename, eg. a diff of foo.c would offer foo.c.diff. Get it from : http://user42.tuxfamily.org/diff-save-buffer/index.html This is designed for use with M-x diff and also M-x vc-diff (the latter actually being compilation-mode). ---- DiffMode