Indentation of preprocessor directives

Question

In my vimrc I have the following line, which figures all the indentation of my files.

filetype plugin indent on

When writing C programs sometimes I use preprocessor directives like #ifdef foo and #endif. When writing one such directive inside a block Vim indents the directive like this.

int main()
{
#ifdef foo
...
#endif
}

But I would like them to be indented as any other statement, i.e.

int main()
{
    #ifdef foo
    ...
    #endif
}

indentkeys might be able to do the job. From :help 'indentkeys'

A list of keys that, when typed in Insert mode, cause reindenting of the current line. Only happens if 'indentexpr' isn't empty.

But my indentexpr is empty and I have no idea what I should put there; or if there is a better solution.

On the Vim wiki I have read

If you plan on using file type based indentation, don't set 'smartindent' or 'cindent'. You may still set 'autoindent', since it doesn't interfere.

So, since I am using file type based indentation I don't want to use smartindent nor cindent.

How can I achieve my intended indentation for preprocessor directives?

Answer 1

This specific behavior is handled by the 'cinkeys' option. 'cinkeys' is similar to 'indentkeys' but is only used when 'cindent' is enabled.

By default, it contains the 0# setting which causes the leading indentation to be removed when a line starts with #. To disable this, you could add

setlocal cinkeys-=0#

to ~/.vim/after/indent/c.vim and ~/.vim/after/indent/cpp.vim.