Compare about using checkout or reset hard to undo git commit

Question

If I use:

$ git reset --hard HEAD~N

or

$ git checkout HEAD~N

Both of two will use the version of HEAD~N to change working directory and stage area.

If there is any different between these two commands?
Thanks.

Answer 1

git checkout HEAD~N is meant to examine the commit and not to be worked on as it will create a detached head state. If you want to reset (the current branch head) to a particular commit, you use git reset [--hard]

Answer 2

• git reset --hard will reset the current branch HEAD to the specified refspec
• git checkout will switch branch, and leave you in a detached head mode.

So with the first, you can start committing right away, in your current branch.
With the second, you need to define a branch first, you (previously) current branch HEAD hasn't move. Only the working directory has been changed. And you are no longer in any branch (hence the "detached mode").