How to prevent cursor shift when using <C-O>{delete cmd} at the end of a line?

Question

<C-w> deletes a (small-)word in insert mode, but I often want to delete the Word (to last whitespace) I've most recently typed. I tried

inoremap <C-_> <C-o>dB

which kind-of works -- except that at the end of the line, <C-o> moves the cursor left one character (and so the last character survives the deletion).

Other options? More generally, how do I use <C-o> in insert-mode mappings without the end-of-line off-by-one problem? Can the normal-mode cursor (which is what <C-o> summons) be placed "temporarily" beyond the line-end?

Answer 1

All you need to do is insert <C-\> before the <C-o>.

inoremap <C-_> <C-\><C-o>dB

Help for i_CTRL-\_CTRL-O says:

CTRL-\ CTRL-O : like CTRL-O but don't move the cursor

That's it. Well except for a caveat or two which I'll reproduce here for your convenience ;) ...

The CTRL-O command sometimes has a side effect: If the cursor was beyond the end of the line, it will be put on the last character in the line. In mappings [you can] use CTRL-\ CTRL-O, but then beware of the cursor possibly being beyond the end of the line. Note that the command following CTRL-\ CTRL-O can still move the cursor, it is not restored to its original position.

While quickly testing your mapping with the fix against the scenario you describe I didn't see any issues so you can probably safely ignore all of that.