Question

Emacs doesn’t automatically indent line for me. For example:

int main() {
   int a;
int b; // this line still don't indent with int a
}

So, how to indent line in Emacs ? And moreover, each time I type {, how to make Emacs automatically indent a tab like other IDEs (eclipse, netbean …) ?

Answer 1

Emacs normal behaviour is to reserve the RET (Enter) key for inserting the carriage return literally, while it uses C-j (Ctrl+J) for entering and indenting. This is also so because of a range of other keys that can cause line to be re-indented. By tradition, the commands that cause re-indentation have “electric” as part of their name. c-mode has a bunch of “electric” commands. To find them, when editing a C source, you can do:

• C-h b (Ctrl+H B) – list all key bindings in the buffer.

• M-s o (Alt PC or Option Mac + S O) – invoke occur command, alternatively, you can M-xoccur.

• Type “electric” when occur prompts you for input (after the previous step, the point will be in minibuffer, so just continue typing).

It will open an additional buffer with the content similar to this:

12 matches for "electric" in buffer: *Help*
    706:C-d             c-electric-delete-forward
    709:#               c-electric-pound
    710:( .. )          c-electric-paren
    711:*               c-electric-star
    712:,               c-electric-semi&comma
    713:/               c-electric-slash
    714::               c-electric-colon
    715:;               c-electric-semi&comma
    716:{               c-electric-brace
    717:}               c-electric-brace
    718:DEL             c-electric-backspace
    726:C-c C-l         c-toggle-electric-state

This lists all the commands and the keys assigned to them, which do some “electric” action. You can move point to any of them and by pressing C-h f (Ctrl+H F) RET it will open the help page describing what exactly the command does. For example, if you request help on c-electric-colon it will show you this:

c-electric-colon is an interactive compiled Lisp function in
`cc-cmds.el'.

(c-electric-colon ARG)

Insert a colon.

If `c-electric-flag' is non-nil, the colon is not inside a literal and a
numeric ARG hasn't been supplied, the command performs several electric
actions:

(a) If the auto-newline feature is turned on (indicated by "/la" on
the mode line) newlines are inserted before and after the colon based on
the settings in `c-hanging-colons-alist'.

(b) Any auto-newlines are indented.  The original line is also
reindented unless `c-syntactic-indentation' is nil.

(c) If auto-newline is turned on, whitespace between two colons will be
"cleaned up" leaving a scope operator, if this action is set in
`c-cleanup-list'.

[back]

You can continue reading the manual from here by moving the point to the item which looks like a hyperlink (usually it is underlined, or has different visual appearance, then the rest of the text), and hit RET. You can use C-b and C-f in *Help* mode to navigate back and forward between the pages you’ve already visited (or move the point to the [back] or [forward] buttons and press RET).