Index: tools/clang-format/clang-format.py
===================================================================
--- tools/clang-format/clang-format.py
+++ tools/clang-format/clang-format.py
@@ -38,7 +38,10 @@
   text = '\n'.join(buf)
 
   # Determine range to format.
-  cursor = int(vim.eval('line2byte(line("."))+col(".")')) - 2
+  cursor = int(vim.eval('line2byte(line("."))')) # line2byte is 1 based.
+  if cursor == -1: # -1 is an error, e.g. empty file
+    return
+  cursor = (cursor - 1) + vim.current.window.cursor[1] # col is 0 based.
   lines = '%s:%s' % (vim.current.range.start + 1, vim.current.range.end + 1)
 
   # Avoid flashing an ugly, ugly cmd prompt on Windows when invoking clang-format.