Indent preprocessor directives as C code in emacs

Question

Emacs, by default, does not indent pre-processor code. I know it has historical roots that are obsolete by now.

However, having a code with a lot of #ifdef unindented is hard to read.

So I would like to make emacs automatic indentation give me something like that:

void myfunc() {
    int foo;

    #ifdef BAR
    printf(foo);
    #endif

    return foo;
}

Instead of what I get now :

void myfunc() {
    int foo;

#ifdef BAR
    printf(foo);
#endif

    return foo;
}

Any leads on that issue you emacs hackers :) ?

Answer 1

You can simply tell Emacs to add an offset to the pre-processor lines.

• Put the cursor (point) in a pre-processor line
• then press C-c C-o (control-c control-o)
• the minibuffer should say Syntactic symbol to change:,
• type cpp-macro, press Enter
• Enter the new offset (number - usually 0)

Then a TAB on each pre-processor line should indent it correctly. (or M-xindent-region ...).

To have the change set permanently, you can for instance add the required lines in your .emacs file.
An easy way to copy a previously entered command is c-x ESC ESC and use the arrow keys to find the (c-set-offset ...) Elisp command.

That should be

(c-set-offset (quote cpp-macro) 0 nil)