Emacs C++-mode incorrect indentation?

问题:

I'm running emacs 23 with c++-mode and having some indentation problems. Suppose I have this code:

void foo()
{
   if (cond)
     { <---
        int i;
        ...
     } <---
}

This seems to be the default behavior of the automatic indentation. However I'd like to change it so it'll be like this:

void foo()
{
   if (cond)
   {
      int i;
      ...
   }
}

Is there a way to do this easily by configuring c++ mode or my .emacs file?

回答1:

I have the following in my .emacs file:

(defun my-c++-mode-hook ()
  (setq c-basic-offset 4)
  (c-set-offset 'substatement-open 0))
(add-hook 'c++-mode-hook 'my-c++-mode-hook)

You can determine which offset to edit by hitting [ctrl-c ctrl-s] on any line. On the first line with a brace after the if it will say substatement-open.

回答2:

This is mine... this matches the default setup for visual studio.

(defun my-c-mode-common-hook ()
 ;; my customizations for all of c-mode, c++-mode, objc-mode, java-mode
 (c-set-offset 'substatement-open 0)
 ;; other customizations can go here

 (setq c++-tab-always-indent t)
 (setq c-basic-offset 4)                  ;; Default is 2
 (setq c-indent-level 4)                  ;; Default is 2

 (setq tab-stop-list '(4 8 12 16 20 24 28 32 36 40 44 48 52 56 60))
 (setq tab-width 4)
 (setq indent-tabs-mode t)  ; use spaces only if nil
 )

(add-hook 'c-mode-common-hook 'my-c-mode-common-hook)

回答3:

Short answer: Put this line into your .emacs file:

(c-set-offset 'substatement-open 0)

Long answer: ...

For those of us who are new to emacs-lisp, there is a pretty simple method at http://www.cs.cmu.edu/:

• Go to the line you want to indent

• Type C-C C-O (that's the letter "O", not zero)

• Press Enter to accept the default suggestion

• Type "0" (that's a zero) for no extra indentation, press Enter

• Type Tab to reindent the line.

• Future "{" in this situation will have the correct tab setting, until you restart emacs.

The nice thing about this method, is that you can actually see the lisp code that you want to change. You can put in your .emacs file:

(c-set-offset 'SYNTACTIC-SYMBOL OFFSET)

Additionally, you may want to check out the program AStyle to automatically format C++ source outside of emacs.

回答4:

The accepted answer is actually wrong. Emacswiki won't help.

Insert following code into ~/.emacs:

(defun fix-c-indent-offset-according-to-syntax-context (key val)
  ;; remove the old element
  (setq c-offsets-alist (delq (assoc key c-offsets-alist) c-offsets-alist))
  ;; new value
  (add-to-list 'c-offsets-alist '(key . val)))

(add-hook 'c-mode-common-hook
          (lambda ()
            (when (derived-mode-p 'c-mode 'c++-mode 'java-mode)
              ;; indent
              (fix-c-indent-offset-according-to-syntax-context 'substatement-open 0))
            ))

See http://blog.binchen.org/posts/ccjava-code-indentation-in-emacs.html for technical details.

The key issue is c-set-offset is not reliable to detect syntax context any more (Emacs24.3.1). So the only reliable way is to analyze the original emacs code. The detailed steps to hack the code is listed in my article, basically you need read the function c-indent-line which is defined in /usr/share/emacs/24.3/lisp/progmodes/cc-cmds.el

Some people complained that my setup does not work. Actually it works in all stable versions of Emacs (23.4, 24.3, 24.4) if you don't change default setup (The indention has different profiles, my setup is based on default profile).

My key point is, on this specific issue, you need read the code.

回答5:

Before tuning individual offsets, configure preferable style. I use stroustrup, you my try some others, see http://www.emacswiki.org/emacs/IndentingC#toc1 for names and http://en.wikipedia.org/wiki/Indent_style#Variant:_Stroustrup for examples

M-x customize-variable c-default-style (and set your preferred for C++_