What's difference between git log and whatchanged?

There is a common request in CI, which is check coding style for changed files.

Original idea is get last commited file list, just like what I did in svn diff --summarize, but didn't get the right way in git.

Finnally, I find git whatchanged -n 1 --name-only --pretty="" almost satisfied my requirement. But if you read man git-whatchanged page, it encouraged you to use git log instead. So, what's difference between git log and whatchanged?

Actually, git whatchanged equals git log --no-merges.