Title says it all really, but to elaborate, in my preferences.txt file, I've changed the editor.tabs.size variable to 4, which works wonderfully, and now produces 4-space tabs as do my other IDEs for all the languages I write in.

However, I was told that using the Tools->AutoFormat feature would update all lines in my previously-written sketches that had the standard 2-space tabs with the new 4-space tab layout.

This isn't so. Whether I CTRL-a to select all and run the Auto Format function, or whether I leave everything de-selected, nothing happens.

Should auto-format "fix" the 'incorrect' indenting to the new style? If so, what am I missing?

I'm currently on Arduino IDE 1.8.5 on Linux Mint, if that makes a difference.

1 Answer 1


The auto formatter (astyle) uses a separate configuration to the editor (crazy, I know, but that's the Arduino mentality for you...).

It uses a separate configuration, which is in the lib folder of your Arduino program, called formatter.conf.

  • Copy that file to the same location as preferences.txt so it doesn't get overwritten when you upgrade the IDE.
  • Edit the file and change indent=spaces=2 to indent=spaces=4

The auto format should now be the same as the editor format.

  • Good grief. I'll test it here shortly @Majenko. Thanks
    – stevieb
    Commented Sep 9, 2019 at 21:24
  • Wow. What a meticulously ridiculous way to do things. Answer accepted as it worked. I'll have to make notes for this and update my automation routines, as I can see this going downhill in the future on new setups.
    – stevieb
    Commented Sep 9, 2019 at 21:28
  • 1
    The auto formatter (astyle) uses a separate configuration to the editor - with what possible justification?
    – Nick Gammon
    Commented Sep 10, 2019 at 9:51
  • @NickGammon I wish I knew. When I implemented astyle in UECIDE it just read the same formatting settings (plus extras that don't apply) for the editor...
    – Majenko
    Commented Sep 10, 2019 at 10:25

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