According to the Vim help, using g CTRL-A with visual mode should change several lines in A to that in B:





In my Vim, the CTRL-A is working in normal mode, which increments a number. But when I am using visual mode, whether it is linewise, block or visual, it will not work. For example, when I press CTRL-A in a help file, it will have this error:

E21: Cannot make changes, 'modifiable' is off

But if I use visual mode, there is no such error and no change happens. The same goes for g CTRL-A and for an editable file.

How can I solve this problem? There are no requisites listed on the manual of this feature, so I probably won't need to recompile the Vim again?


  1. E21 is not the real problem, I just want to use it as an indicator that it doesn't work, i.e. it doesn't change or try to change anything.

  2. :ver first line output:

     VIM - Vi IMproved 7.4 (2013 Aug 10, compiled Apr 13 2016 12:09:32)

    Included patches: 1-1725

  • IIRC using <C-a> in visual mode was added fairly recently. Which Vim version are you using? Apr 5, 2016 at 4:59
  • Just for the record where is the doc saying that g CTRL-A increments numbers in visual mode? My Vim 7.4 :h g_CTRL-A says that it is used to print memory usage statistics for debugging Vim.
    – statox
    Apr 5, 2016 at 7:27
  • @statox see :h v_g_CTRL-A. I think Carpetsmoker's right and this has to do with the Vim version. On Arch, or with the pi-rho PPA on Ubuntu 14.04, this works, but on Ubuntu 14.04 with the repository Vim (7.4, patches 1-52), it doesn't work.
    – muru
    Apr 5, 2016 at 7:54
  • @muru Thanks for the link I didn't find the topic because it is not included in my version so I think you and Carpetsmoker are right it must be because OP doesn't have the correct version.
    – statox
    Apr 5, 2016 at 8:11
  • How can we download such a version of Vim? I have updated mine and it still is not correct. Cloning the git file on github is also not working. May 3, 2016 at 21:56

1 Answer 1


Seems like c-a has been mapped to some plugin in your vim. (In that plugin, c-a is mapped to some 'modifiable' action, so that you get that error message....) You might try :vmap to list all key mappings in visual mode and check if there is some plugin or custom key binding who is using c-a.

  • This doesn't account for g<C-a> not working... Apr 5, 2016 at 5:45
  • ah....i read the post again, and found out it could be related to 'help files', if you try to 'modify' in that read-only split window, E21 is the error message. Just tried that and got E21, this could be the reason, but it has nothing to do with a normal editable file, just provide more clues here.
    – Philia Fan
    Apr 5, 2016 at 5:53
  • 1
    Actually not only help buffer are affected by the modifiable setting: The user can use set nomodifiable to other buffers if he wishes. See :h 'modifiable'
    – statox
    Apr 5, 2016 at 7:32
  • Actually, E21 is not the problem, I just want to use it as an indicator that it doesn't work, i.e. it doesn't change or try to change anything.
    – Chromium
    May 4, 2016 at 3:21

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