Copyright © 1995, 1996 Free Software Foundation, Inc.

Introduction
************

Welcome to CC Mode, version 4.  This is a GNU Emacs mode for editing files containing C, C++, Objective-C, and Java code. This incarnation of the mode is descendant from c-mode.el (also called "Boring Old C Mode" or BOCM :-), and c++-mode.el version 2, which I have been maintaining since 1992.  CC Mode represents a significant milestone in the mode's life.  It has been fully merged back with Emacs 19's c-mode.el. Also a new, more intuitive and flexible mechanism for controlling indentation has been developed.

CC Mode version 4 supports the editing of K&R and ANSI C, ARM (``The Annotated C++ Reference Manual'', by Ellis and Stroustrup.) C++, Objective-C, and Java files.  In this way, you can easily set up consistent coding styles for use in editing all C, C++, Objective-C, and Java programs. CC Mode does not handle font-locking (a.k.a. syntax coloring, keyword highlighting) or anything of that nature, for any of the 4 modes.  Those are handled by other Emacs packages.

This manual will describe the following:

  * How to get started using CC Mode.

  * How the new indentation engine works.

  * How to customize the new indentation engine.

Note that the name of this package is ``CC Mode''.  The main file for CC Mode is cc-mode.el, but other files are included in the CC Mode distribution.  There is no top level cc-mode entry point.  All of the variables, commands, and functions in CC Mode are prefixed with c-<THING>, and c-mode, c++-mode, objc-mode, and java-mode entry points are provided.  This file is intended to be a replacement for c-mode.el and c++-mode.el.

The major version number was incremented to 4 with the addition of objc-mode. To find the minor revision number of this release, use M-x c-version RET.

As of this writing (27-Feb-1997), Emacs 19.34, XEmacs 19.14, and XEmacs 20.0 are all distributed with CC Mode, but they may not have the latest releases.  You may therefore, want to upgrade your copy of CC Mode.  See Getting the latest CC Mode release.

This distribution also contains a file called cc-compat.el which should ease your transition from BOCM to CC Mode.  It currently comes unguaranteed and unsupported, but this may change for future versions.  If you have a BOCM configuration you are really happy with, and want to postpone learning how to configure CC Mode, take a look at that file.  It maps BOCM configuration variables to CC Mode's new indentation model.

A special word of thanks goes to Krishna Padmasola for his work in converting the original README file to texinfo format.

Getting Connected
*****************

cc-mode.el works well with the three main branches of Emacs: XEmacs 19 and XEmacs 20, both maintained by xemacs.org, and Emacs 19 maintained by the Free Software Foundation.  Emacs users will want to use version 19.21 or better, XEmacs users will want 19.6 or better. Earlier versions of these Emacsen have deficiencies and/or bugs which will adversely affect the performance and usability of CC Mode.  You are better off just getting the latest version of Emacs or XEmacs.

cc-mode.el will work with Emacs 18 if you use the cc-mode-18.el compatibility file, but only moderately well.  A word of warning though, Emacs 18 lacks some fundamental
functionality and ultimately, using Emacs 18 is a losing
battle.  Hence CC Mode under Emacs 18 is no longer supported and it is highly recommended that you upgrade to Emacs 19.  If you use CC Mode under Emacs 18, you're on your own.  With CC Mode version 5, Emacs 18 support will be dropped altogether.

Note that as of XEmacs 19.13 and Emacs 19.30, your Emacs already comes with CC Mode version 4 preconfigured for your use.  You should be able to safely skip the rest of the setup information in this chapter, unless you want to install the latest version of CC Mode into one of these Emacsen.

The first thing you will want to do is put cc-mode.el somewhere on your load-path so Emacs can find it.  Do a C-h v load-path RET to see all the directories Emacs looks at when loading a file.  If none of these directories are appropriate, create a new directory and add it to your load-path:

[in the shell]

     % cd
     % mkdir mylisp
     % mv cc-mode.el mylisp
     % cd mylisp

[in your .emacs file add]

     (setq load-path (cons "~/mylisp" load-path))

Next you want to byte compile cc-mode.el.  The mode uses a lot of macros so if you don't byte compile it, things will be unbearably slow.  You can ignore all byte-compiler warnings!  They are the result of the supporting different versions of Emacs, and none of the warnings have any effect on operation. Let me say this again: You really can ignore all byte-compiler warnings!

Here's what to do to byte-compile the file [in emacs]:

     M-x byte-compile-file RET ~/mylisp/cc-mode.el RET

If you are running a version of Emacs or XEmacs that comes with CC Mode by default, you can simply add the following to your .emacs file in order to upgrade to the latest version of CC Mode:

     (load "cc-mode")

Users of even older versions of Emacs 19, Emacs 18, or of the older Lucid Emacs will probably be running an Emacs that has BOCM c-mode.el and possible c++-mode.el pre-dumped.  If your Emacs is dumped with either of these files you first need to make Emacs ``forget'' about those older modes.

If you can do a C-h v c-mode-map RET without getting an error, you need to add these lines at the top of your .emacs file:

     (fmakunbound 'c-mode)
     (makunbound  'c-mode-map)
     (fmakunbound 'c++-mode)
     (makunbound  'c++-mode-map)
     (makunbound  'c-style-alist)

After those lines you will want to add the following autoloads to your .emacs file so that CC Mode gets loaded at the right time:

     (autoload 'c++-mode  "cc-mode" "C++ Editing Mode" t)
     (autoload 'c-mode    "cc-mode" "C Editing Mode" t)
     (autoload 'objc-mode "cc-mode" "Objective-C Editing Mode" t)
     (autoload 'java-mode "cc-mode" "Java Editing Mode" t)

Alternatively, if you want to make sure CC Mode is loaded when Emacs starts up, you could use this line instead of the autoloads above:

     (require 'cc-mode)

Next, you will want to set up Emacs so that it edits C files in c-mode, C++ files in c++-mode, Objective-C files in objc-mode, and Java files in java-mode. You should add the following to your .emacs file, which assumes you'll be editing .h and .c files as C, .hh, .cc, .H, and .C files as C++, .m files as Objective-C, and .java files as Java code. YMMV:

     (setq auto-mode-alist
       (append
         '(("\\.C$"    . c++-mode)
           ("\\.H$"    . c++-mode)
           ("\\.cc$"   . c++-mode)
           ("\\.hh$"   . c++-mode)
           ("\\.c$"    . c-mode)
           ("\\.h$"    . c-mode)
           ("\\.m$"    . objc-mode)
           ("\\.java$" . java-mode)
          ) auto-mode-alist))

You may already have some or all of these settings on your auto-mode-alist, but it won't hurt to put them on there again.

That's all you need --- I know, I know, it sounds like a lot :-), but after you've done all this, you should only need to quit and restart Emacs.  The next time you visit a C, C++, Objective-C, or Java file you should be using CC Mode.  You can check this easily by hitting M-x c-version RET; you should see this message in the echo area:

     Using CC Mode version 4.XXX

where XXX is the latest minor release number.

New Indentation Engine
**********************

CC Mode has a new indentation engine, providing a simplified, yet flexible and general mechanism for customizing indentation. It separates indentation calculation into two steps: first, CC Mode analyzes the line of code being indented to determine the kind of language construct it's looking at, then it applies user defined offsets to the current line based on this analysis.

This section will briefly cover how indentation is calculated in CC Mode. It is important to understand the indentation model being used so that you will know how to customize CC Mode for your personal coding style.

Syntactic Analysis
==================

The first thing CC Mode does when indenting a line of code, is to analyze the line, determining the syntactic component list of the construct on that line.  A syntactic component consists of a pair of information (in lisp parlance, a cons cell), where the first part is a syntactic symbol, and the second part is a relative buffer position.  Syntactic symbols describe elements of C code (or C++, Objective-C, or Java code.  In general, for the rest of this manual I'll use the term ``C code'' to refer to all the C-like dialects, unless otherwise noted.), e.g. statement, substatement, class-open, class-close, etc. See Syntactic Symbols, for a complete list of currently recognized syntactic symbols and their semantics.  The variable c-offsets-alist also contains the list of currently supported syntactic symbols.

Conceptually, a line of C code is always indented relative to the indentation of some line higher up in the buffer.  This is represented by the relative buffer position in the syntactic component.

Here is an example.  Suppose we had the following code as the only thing in a c++-mode buffer  (The line numbers in this and future examples don't actually appear in the buffer, of course!):

       1: void swap( int& a, int& b )
       2: {
       3:     int tmp = a;
       4:     a = b;
       5:     b = tmp;
       6: }

We can use the command C-c C-s (c-show-syntactic-information) to simply report what the syntactic analysis is for the current line.  Running this command on line 4 this example, we'd see in the echo area (With a universal argument (i.e. C-u C-c C-s) the analysis is inserted into the buffer as a comment on the current line.):

     ((statement . 35))

This tells us that the line is a statement and it is indented relative to buffer position 35, which happens to be the i in int on line 3.  If you were to move point to line 3 and hit C-c C-s, you would see:

     ((defun-block-intro . 29))

This indicates that the int line is the first statement in a top level function block, and is indented relative to buffer position 29, which is the brace just after the function header.

Here's another example:

       1: int add( int val, int incr, int doit )
       2: {
       3:     if( doit )
       4:         {
       5:             return( val + incr );
       6:         }
       7:     return( val );
       8: }

Hitting C-c C-s on line 4 gives us:

     ((substatement-open . 46))

which tells us that this is a brace that opens a substatement block.  (A substatement indicates the line after a conditional statement, such as if, else, while, do, switch, or for in C.  A substatement block is a brace block following one of those conditionals.)

Syntactic component lists can contain more than one component, and individual syntactic components need not have relative buffer positions. The most common example of this is a line that contains a comment only line.

       1: void draw_list( List<Drawables>& drawables )
       2: {
       3:         // call the virtual draw() method on each element in list
       4:     for( int i=0; i < drawables.count(), ++i )
       5:     {
       6:         drawables[i].draw();
       7:     }
       8: }

Hitting C-c C-s on line 3 of this example gives:

     ((comment-intro) (defun-block-intro . 46))

and you can see that the syntactic component list contains two syntactic components.  Also notice that the first component, (comment-intro) has no relative buffer position.

Indentation Calculation
=======================

Indentation for the current line is calculated using the syntactic component list derived in step 1 above (see Syntactic Analysis). Each component contributes to the final total indentation of the line in two ways.

First, the syntactic symbols are looked up in the c-offsets-alist variable, which is an association list of syntactic symbols and the offsets to apply for those symbols.  These offsets are added to a running total.

Second, if the component has a relative buffer position, CC Mode adds the column number of that position to the running total.  By adding up the offsets and columns for every syntactic component on the list, the final total indentation for the current line is computed.

Let's use our two code examples above to see how this works.  Here is our first example again:

         1: void swap( int& a, int& b )
         2: {
         3:     int tmp = a;
         4:     a = b;
         5:     b = tmp;
         6: }

Let's say point is on line 3 and we hit the TAB key to re-indent the line.  Remember that the syntactic component list for that line is:

     ((defun-block-intro . 29))

CC Mode looks up defun-block-intro in the c-offsets-alist variable.  Let's say it finds the value 4; it adds this to the running total (initialized to zero), yielding a running total indentation of 4 spaces.

Next CC Mode goes to buffer position 29 and asks for the current column.  This brace is in column zero, so CC Mode adds 0 to the running total.  Since there is only one syntactic component on the list for this line, indentation calculation is complete, and the total indentation for the line is 4 spaces.

Here's another example:

         1: int add( int val, int incr, int doit )
         2: {
         3:     if( doit )
         4:         {
         5:             return( val + incr );
         6:         }
         7:     return( val );
         8: }

If we were to hit TAB on line 4 in the above example, the same basic process is performed, despite the differences in the syntactic component list.  Remember that the list for this line is:

     ((substatement-open . 46))

Here, CC Mode first looks up the substatement-open symbol in c-offsets-alist. Let's say it finds the value 4.  This yields a running total of 4.  CC Mode then goes to buffer position 46, which is the i in if on line 3.  This character is in the fourth column on that line so adding this to the running total yields an indentation for the line of 8 spaces.

Simple, huh?

Actually, the mode usually just does The Right Thing without you having to think about it in this much detail.  But when customizing indentation, it's helpful to understand the general indentation model being used.

As you configure CC Mode, you might want to set the variable c-echo-syntactic-information-p to non-nil so that the syntactic component list and calculated offset will always be echoed in the minibuffer when you hit TAB.

Minor Modes
***********

CC Mode contains two minor-mode-like features that you should find useful while you enter new C code.  The first is called auto-newline mode, and the second is called hungry-delete mode.  These minor modes can be toggled on and off independently, and CC Mode can be configured so that it starts up with any combination of these minor modes.  By default, both of these minor modes are turned off.

The state of the minor modes is always reflected in the minor mode list on the modeline of the CC Mode buffer.  When auto-newline mode is enabled, you will see C/a on the mode line  (Remember that the C could be replaced with C++, ObjC, or Java.).  When hungry delete mode is enabled you would see C/h and when both modes are enabled, you'd see C/ah.

CC Mode provides keybindings which allow you to toggle the minor modes on the fly while editing code.  To toggle just the auto-newline state, hit C-c C-a (c-toggle-auto-state).  When you do this, you should see the a indicator either appear or disappear on the modeline.  Similarly, to toggle just the hungry-delete state, use C-c C-d (c-toggle-hungry-state), and to toggle both states, use C-c C-t (c-toggle-auto-hungry-state).

To set up the auto-newline and hungry-delete states to your preferred values, you would need to add some lisp to your .emacs file that called one of the c-toggle-*-state functions directly.  When called programmatically, each function takes a numeric value, where a positive number enables the minor mode, a negative number disables the mode, and zero toggles the current state of the mode.

So for example, if you wanted to enable both auto-newline and hungry-delete for all your C file editing, you could add the following to your .emacs file:

     (add-hook 'c-mode-common-hook
     	  '(lambda () (c-toggle-auto-hungry-state 1)))

Auto-newline insertion
======================

Auto-newline minor mode works by enabling certain electric commands.  Electric commands are typically bound to special characters such as the left and right braces, colons, semi-colons, etc., which when typed, perform some magic formatting in addition to inserting the typed character.  As a general rule, electric commands are only electric when the following conditions apply:

  * Auto-newline minor mode is enabled, as evidenced by a C/a or C/ah indicator on the modeline.

  * The character was not typed inside of a literal  (A literal is defined as any comment, string, or cpp macro definition.  These constructs are also known as syntactic whitespace since they are usually ignored when scanning C code.).

  * No numeric argument was supplied to the command (i.e. it was typed as normal, with no C-u prefix).

Some characters are electric in some languages, and not in others.  For example, the second slash (/) of a C++ style line comment is electric in c++-mode, objc-mode, and java-mode, but not in c-mode (Ordinarily, // does not introduce a comment in c-mode.  However, if you call the function c-enable-//-in-c-mode, c-mode will recognize C++ style line comments.  Note however that this is a global change which will affect all your c-mode buffers.).

Hanging Braces
--------------

When you type either an open or close brace (i.e. { or }), the electric command c-electric-brace gets run.  This command has two electric formatting behaviors.  First, it will perform some re-indentation of the line the brace was typed on, and second, it will add various newlines before and/or after the typed brace. Re-indentation occurs automatically whenever the electric behavior is enabled.  If the brace ends up on a line other than the one it was typed on, then that line is also indented according to c-offsets-alist.

The insertion of newlines is controlled by the c-hanging-braces-alist variable.  This variable contains a mapping between syntactic symbols related to braces, and a list of places to insert a newline.  The syntactic symbols that are useful for this list are: class-open, class-close, defun-open, defun-close, inline-open, inline-close, brace-list-open, brace-list-close, brace-list-intro, brace-list-entry, block-open, block-close, substatement-open, statement-case-open, extern-lang-open, and extern-lang-close. See Syntactic Symbols for a more detailed description of these syntactic symbols.

The value associated with each syntactic symbol in this association list is called an ACTION which can be either a function or a list. See Custom Brace and Colon Hanging for a more detailed discussion of using a function as a brace hanging ACTION.

When the ACTION is a list, it can contain any combination of the symbols before and after, directing CC Mode where to put newlines in relationship to the brace being inserted.  Thus, if the list contains only the symbol after, then the brace is said to hang on the right side of the line, as in:

     // here, open braces always `hang'
     void spam( int i ) {
         if( i == 7 ) {
             dosomething(i);
         }
     }

When the list contains both after and before, the braces will appear on a line by themselves, as shown by the close braces in the above example.  The list can also be empty, in which case no newlines are added either before or after the brace.

For example, the default value of c-hanging-braces-alist is:

     (defvar c-hanging-braces-alist '((brace-list-open)
                                      (substatement-open after)
                                      (block-close . c-snug-do-while)
                                      (extern-lang-open after)))

which says that brace-list-open braces should both hang on the right side, and allow subsequent text to follow on the same line as the brace.  Also, substatement-open and extern-lang-open braces should hang on the right side, but subsequent text should follow on the next line.  Here, in the block-close entry, you also see an example of using a function as an ACTION.

A word of caution: it is not a good idea to hang top-level construct introducing braces, such as class-open or defun-open. Emacs makes an assumption that such braces will always appear in column zero, hanging such braces can introduce performance problems. See Performance Issues for more information.

Hanging Colons
--------------

Using a mechanism similar to brace hanging (see Hanging Braces), colons can also be made to hang using the variable c-hanging-colons-alist.  The syntactic symbols appropriate for this assocation list are: case-label, label, access-label, member-init-intro, and inher-intro. Note however, that for c-hanging-colons-alist ACTIONs as functions are not supported. See also Custom Brace and Colon Hanging for details.

In C++, double-colons are used as a scope operator but because these colons always appear right next to each other, newlines before and after them are controlled by a different mechanism, called clean-ups in CC Mode.  See Clean-ups for details.

Hanging Semi-colons and commas
------------------------------

Semicolons and commas are also electric in CC Mode, but since these characters do not correspond directly to syntactic symbols, a different mechanism is used to determine whether newlines should be automatically inserted after these characters.  See Customizing Semi-colons and Commas for details.

Other electric commands
-----------------------

A few other keys also provide electric behavior.  For example # (c-electric-pound) is electric when typed as the first non-whitespace character on a line.  In this case, the variable c-electric-pound-behavior is consulted for the electric behavior.  This variable takes a list value, although the only element currently defined is alignleft, which tells this command to force the # character into column zero.  This is useful for entering cpp macro definitions.

Stars and slashes (i.e. * and /, c-electric-star and c-electric-slash respectively) are also electric under certain circumstances.  If a star is inserted as the second character of a C style block comment on a comment-only line, then the comment delimiter is indented as defined by c-offsets-alist.  A comment-only line is defined as a line which contains only a comment, as in:

     void spam( int i )
     {
             // this is a comment-only line...
         if( i == 7 )                             // but this is not
         {
             dosomething(i);
         }
     }

Likewise, if a slash is inserted as the second slash in a C++ style line comment (also only on a comment-only line), then the line is indented as defined by c-offsets-alist.

Less-than and greater-than signs (c-electric-lt-gt) are also electric, but only in C++ mode.  Hitting the second of two < or > keys re-indents the line if it is a C++ style stream operator.

Clean-ups
---------

Clean-ups are a mechanism complementary to colon and brace hanging.  On the surface, it would seem that clean-ups overlap the functionality provided by the c-hanging-*-alist variables, and similarly, clean-ups are only enabled when auto-newline minor mode is enabled.  Clean-ups are used however to adjust code ``after-the-fact'', i.e. to eliminate some whitespace that isn't inserted by electric commands, or whitespace that contains intervening constructs.

You can configure CC Mode's clean-ups by setting the variable c-cleanup-list, which is a list of clean-up symbols.  By default, CC Mode cleans up only the scope-operator construct, which is necessary for proper C++ support.  Note that clean-ups are only performed when the construct does not occur within a literal (see Auto-newline insertion), and when there is nothing but whitespace appearing between the individual components of the construct.

There are currently only five specific constructs that CC Mode can clean up, as indicated by these symbols:

  * brace-else-brace --- cleans up } else { constructs by placing the entire construct on a single line.  Clean-up occurs when the open brace after the else is typed.  So for example, this:

          void spam(int i)
          {
              if( i==7 )
              {
                  dosomething();
              }
              else
              {

     appears like this after the open brace is typed:

          void spam(int i)
          {
              if( i==7 ) {
                  dosomething();
              } else {

  * brace-elseif-brace --- similar to the brace-else-brace clean-up, but cleans up } else if (...){ constructs.  For example:

          void spam(int i)
          {
              if( i==7 )
              {
                  dosomething();
              }
              else if( i==3 ) {

     appears like this after the open brace is typed:

          void spam(int i)
          {
              if( i==7 ) {
                  dosomething();
              } else if( i==3 ) {

  * empty-defun-braces --- cleans up braces following a top-level function or class definition that contains no body.  Clean up occurs when the closing brace is typed.  Thus the following:

          class Spam
          {
          }

     is transformed into this when the close brace is typed:

          class Spam
          {}

  * defun-close-semi --- cleans up the terminating semi-colon on top-level function or class definitions when they follow a close brace. Clean up occurs when the semi-colon is typed. So for example, the following:

          class Spam
          {
          }
          ;

     is transformed into this when the semi-colon is typed:

          class Spam
          {
          };

  * list-close-comma --- cleans up commas following braces in array and aggregate initializers.  Clean up occurs when the comma is typed.

  * scope-operator --- cleans up double colons which may designate a C++ scope operator split across multiple lines (Certain C++ constructs introduce ambiguous situations, so scope-operator clean-ups may not always be correct.  This usually only occurs when scoped identifiers appear in switch label tags.).  Clean up occurs when the second colon is typed.  You will always want scope-operator in the c-cleanup-list when you are editing C++ code.

Hungry-deletion of whitespace
=============================

Hungry deletion of whitespace, or as it more commonly called, hungry-delete mode, is a simple feature that some people find extremely useful.  In fact, you might find yourself wanting hungry-delete in all your editing modes!

In a nutshell, when hungry-delete mode is enabled, hitting the DEL character will consume all preceding whitespace, including newlines and tabs.  This can really cut down on the number of DEL's you have to type if, for example you made a mistake on the preceding line.

By default, CC Mode actually runs the command c-electric-delete when you hit DEL.  When this command is used to delete a single character (i.e. when it is called interactively with no numeric argument), it really runs the function contained in the variable c-delete-function.  This function is called with a single argument, which is the number of characters to delete. c-delete-function is also called when the DEL key is typed inside a literal (see Auto-newline insertion.  Inside a literal, c-electric-delete is not electric, which is typical of all the so-called electric commands.

Commands
********

Indentation Commands
====================

Various commands are provided which allow you to conveniently re-indent C constructs.  There are several things to note about these indentation commands.  First, when you change your programming style, either interactively or through some other means, your file does not automatically get re-indented. When you change style parameters, you will typically need to reformat the line, expression, or buffer to see the effects of your changes.

Second, changing some variables have no effect on existing code, even when you do re-indent.  For example, the c-hanging-* variables and c-cleanup-list only affect new code as it is typed in on-the-fly, so changing c-hanging-braces-alist and re-indenting the buffer will not adjust placement of braces already in the file.

Third, re-indenting large portions of code is currently rather inefficient.  Improvements have been made since previous releases of CC Mode, and much more radical improvements are planned, but for now you need to be aware of this  (In particular, I have had people complain about the speed with which lex(1) output is re-indented. Lex, yacc, and other code generators usually output some pretty perversely formatted code.  Don't try to indent this stuff!). Some provision has been made to at least inform you as to the progress of the re-indentation.  The variable c-progress-interval controls how often a progress message is displayed.  Set this variable to nil to inhibit progress messages.  Note that this feature only works with Emacs 19 and beyond.

Also, except as noted below, re-indentation is always driven by the same mechanisms that control on-the-fly indentation of code.  See New Indentation Engine for details.

To indent a single line of code, use TAB (c-indent-command).  The behavior of this command is controlled by the variable c-tab-always-indent.  When this variable is t, TAB always just indents the current line.  When nil, the line is indented only if point is at the left margin, or on or before the first non-whitespace character on the line, otherwise something else happens (Actually what happens is that the function stored in c-insert-tab-function is called. Normally this just inserts a real tab character, or the equivalent number of spaces, depending on the setting of the variable indent-tabs-mode.  If you preferred, you could set c-insert-tab-function to tab-to-tab-stop for example.). If the value of c-tab-always-indent is something other than t or nil (e.g. 'other), then a real tab character (The caveat about indent-tabs-mode in the previous footnote also applies here.)  is inserted only when point is inside a literal (see Auto-newline insertion), otherwise the line is indented.

To indent an entire balanced brace or parenthesis expression, use M-C-q (c-indent-exp).  Note that point should be on the opening brace or parenthesis of the expression you want to indent.

Another very convenient keystroke is C-c C-q (c-indent-defun) when re-indents the entire top-level function or class definition that encompases point.  It leaves point at the same position within the buffer.

To indent any arbitrary region of code, use M-C-\ (indent-region).   This is a standard Emacs command, specially tailored for C code in a CC Mode buffer.  Note that of course, point and mark must delineate the region you want to indent.

While not strictly an indentation function, M-C-h (c-mark-function) is useful for marking the current top-level function or class definition as the current region.

Other Commands
==============

CC Mode contains other useful command for moving around in C code.

C-c C-u (c-up-conditional)
     Move point back to the containing preprocessor conditional, leaving the mark behind.  A prefix argument acts as a repeat count.  With a negative argument, move point forward to the end of the containing preprocessor conditional.  When going backwards, #elif is treated like #else followed by #if.  When going forwards, #elif is ignored.

C-c C-p (c-backward-conditional)
     Move point back over a preprocessor conditional, leaving the mark behind.  A prefix argument acts as a repeat count.  With a negative argument, move forward.

C-c C-n (c-forward-conditional)
     Move point forward across a preprocessor conditional, leaving the mark behind.  A prefix argument acts as a repeat count.  With a negative argument, move backward.

M-a (c-beginning-of-statement)
     Move point to the beginning of the innermost C statement.  If point is already at the beginning of a statement, it moves to the beginning of the preceding statement.  With prefix argument N, move back N - 1 statements.

     If point is within a string or comment, or at the end of a comment, this command moves by sentences instead of statements.

     When called from a program, this function takes three optional arguments: the numeric prefix argument, a buffer position limit (don't move back before that place), and a flag to indicate whether movement should be by statements (if t) or sentence (if non-nil).

M-e (c-end-of-statement)
     Move point to the end of the innermost C statement.  If point is at the end of a statement, move to the end of the next statement.  With prefix argument N, move forward N - 1 statements.

     If point is within a string or comment, or at the end of a comment, this command moves by sentences instead of statements.

     When called from a program, this function takes three optional arguments: the numeric prefix argument, a buffer position limit (don't move back before that place), and a flag to indicate whether movement should be by statements (if t) or sentence (if non-nil).

M-x c-forward-into-nomenclature
     A popular programming style, especially for object-oriented languages such as C++ is to write symbols in a mixed case format, where the first letter of each word is capitalized, and not separated by underscores. E.g. SymbolsWithMixedCaseAndNoUnderlines.

     This command moves point forward to end of a C++ nomenclature section or word.  With prefix argument N, move N times.

M-x c-backward-into-nomenclature
     Move point backward to beginning of a C++ nomenclature section or word.  With prefix argument N, move N times.  If N is negative, move forward.

C-c : (c-scope-operator)
     In C++, it is also sometimes desirable to insert the double-colon scope operator without performing the electric behavior of colon insertion. C-c : does just this.

M-q (fill-paragraph)
     The command is used to fill a block style (C) or line style (C++) comment, in much the same way that text in the various text modes can be filled.  You should never attempt to fill non-comment code sections; you'll end up with garbage!  Two variables control how C style block comments are filled, specifically how the comment start and end delimiters are handled.

     The variable c-hanging-comment-starter-p controls whether comment start delimiters which appear on a line by themselves, end up on a line by themselves after the fill.  When the value is nil, the comment starter will remain on its own line (It will not be placed on a separate line if it is not already on a separate line.).  Otherwise, text on the next line will be put on the same line as the comment starter.  This is called hanging because the following text hangs on the line with the comment starter.

     The variable c-hanging-comment-ender-p controls the analogous behavior for the block comment end delimiter.  When the value is nil, the comment ender will remain on its own line after the file (The same caveat as above holds true.).  Otherwise, the comment end delimiter will be placed at the end of the previous line.

Customizing Indentation
***********************

The variable c-offsets-alist contains the mappings between syntactic symbols and the offsets to apply for those symbols.  You should never modify this variable directly though.  Use the function c-set-offset instead (see below for details).

The c-offsets-alist variable is where you customize all your indentations.  You simply need to decide what additional offset you want to add for every syntactic symbol.  You can use the command C-c C-o (c-set-offset) as the way to set offsets, both interactively and from your mode hook.  Also, you can set up styles of indentation just like in BOCM.  Most likely, you'll find one of the pre-defined styles will suit your needs, but if not, this section will describe how to set up basic editing configurations. See Styles for an explanation of how to set up named styles.

As mentioned previously, the variable c-offsets-alist is an association list of syntactic symbols and the offsets to be applied for those symbols.  In fact, these offset values can be any of an integer, a function or lambda expression, a variable name, or one of the following symbols: +, -, ++, --, *, or /.  These symbols describe offset in multiples of the value of the variable c-basic-offset.  By defining a style's indentation in terms of this fundamental variable, you can change the amount of whitespace given to an indentation level while leaving the same relationship between levels.  Here are the values that the special symbols correspond to:

+
     c-basic-offset times 1

-
     c-basic-offset times -1

++
     c-basic-offset times 2

--
     c-basic-offset times -2

*
     c-basic-offset times 0.5

/
     c-basic-offset times -0.5

So, for example, because most of the default offsets are defined in terms of +, -, and 0, if you like the general indentation style, but you use 4 spaces instead of 2 spaces per level, you can probably achieve your style just by changing c-basic-offset like so (in your .emacs file) (The reason you need to use setq-default instead of setq is that c-basic-offset is a buffer local variable, as are most configuration variables.  If you were to put this code in, e.g. your c-mode-common-hook function, you could use setq. Alternatively, you can keep these variables global by setting c-style-variables-are-local-p to nil, but you must do this before cc-mode.el is loaded into your Emacs session.):

     (setq-default c-basic-offset 4)

This would change

     int add( int val, int incr, int doit )
     {
       if( doit )
         {
           return( val + incr );
         }
       return( val );
     }

to

     int add( int val, int incr, int doit )
     {
         if( doit )
             {
                 return( val + incr );
             }
         return( val );
     }

To change indentation styles more radically, you will want to change the value associated with the syntactic symbols in the c-offsets-alist variable.  First, I'll show you how to do that interactively, then I'll describe how to make changes to your .emacs file so that your changes are more permanent.

Interactive Customization
=========================

As an example of how to customize indentation, let's change the style of this example (In this an subsequent examples, the original code is formatted using the gnu style unless otherwise indicated. See Styles.):

     1: int add( int val, int incr, int doit )
     2: {
     3:   if( doit )
     4:     {
     5:       return( val + incr );
     6:     }
     7:   return( val );
     8: }

to:

     1: int add( int val, int incr, int doit )
     2: {
     3:   if( doit )
     4:   {
     5:     return( val + incr );
     6:   }
     7:   return( val );
     8: }

In other words, we want to change the indentation of braces that open a block following a condition so that the braces line up under the conditional, instead of being indented.  Notice that the construct we want to change starts on line 4.  To change the indentation of a line, we need to see which syntactic components affect the offset calculations for that line.  Hitting C-c C-s on line 4 yields:

     ((substatement-open . 44))

so we know that to change the offset of the open brace, we need to change the indentation for the substatement-open syntactic symbol.  To do this interactively, just hit C-c C-o (c-set-offset).  This prompts you for the syntactic symbol to change, providing a reasonable default.  In this case, the default is substatement-open, which is just the syntactic symbol we want to change!

After you hit return, CC Mode will then prompt you for the new offset value, with the old value as the default.  The default in this case is +, but we want no extra indentation so enter 0 and RET.  This will associate the offset 0 with the syntactic symbol substatement-open in the c-offsets-alist variable.

To check your changes quickly, just hit C-c C-q (c-indent-defun) to reindent the entire function.  The example should now look like:

     1: int add( int val, int incr, int doit )
     2: {
     3:   if( doit )
     4:   {
     5:     return( val + incr );
     6:   }
     7:   return( val );
     8: }

Notice how just changing the open brace offset on line 4 is all we needed to do.  Since the other affected lines are indented relative to line 4, they are automatically indented the way you'd expect.  For more complicated examples, this may not always work.  The general approach to take is to always start adjusting offsets for lines higher up in the file, then re-indent and see if any following lines need further adjustments.

Permanent Customization
=======================

To make this change permanent, you need to add some lisp code to your .emacs file.  CC Mode provides several hooks that you can use to customize the mode according to your coding style.  Each language mode has its own hook, adhering to standard Emacs major mode conventions.  There is also one general hook:

  * c-mode-hook --- for C buffers only

  * c++-mode-hook --- for C++ buffers only

  * objc-mode-hook --- for Objective-C buffers only

  * java-mode-hook --- for Java buffers only

  * c-mode-common-hook --- common across all languages

The language hooks get run as the last thing when you enter that language-specific mode.  The c-mode-common-hook is run by all supported modes before the language specific hook, and thus can contain customizations that are common across all languages.  Most of the examples in this section will assume you are using the common hook (The interaction between java-mode and the hook variables is slightly different than for the other modes. java-mode sets the style (see Styles) of the buffer to java before running the c-mode-common-hook or java-mode-hook.  You need to be aware of this so any style settings in c-mode-common-hook doesn't clobber your Java style.).

Here's a simplified example of what you can add to your .emacs file to make the changes described in the previous section (Interactive Customization) more permanent.  See the Emacs manuals for more information on customizing Emacs via hooks.  See Sample .emacs File for a more complete sample .emacs file. (The use of add-hook in this example only works for Emacs 19 and beyond.  Workarounds are available if you are using Emacs 18.)

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

For complex customizations, you will probably want to set up a style that groups all your customizations under a single name.

Styles
======

Most people only need to edit code formatted in just a few well-defined and consistent styles.  For example, their organization might impose a ``blessed'' style that all its programmers must conform to.  Similarly, people who work on GNU software will have to use the GNU coding style on C code.  Some shops are more lenient, allowing some variety of coding styles, and as programmers come and go, there could be a number of styles in use.  For this reason, CC Mode makes it convenient for you to set up logical groupings of customizations called styles, associate a single name for any particular style, and pretty easily start editing new or existing code using these styles.  This section describes how to set up styles and how to edit your C code using styles.

Built-in Styles
---------------

If you're lucky, one of CC Mode's built-in styles might be just what you're looking for.  These include:

  * gnu --- coding style blessed by the Free Software Foundation for C code in GNU programs.

  * k&r --- The classic Kernighan and Ritchie style for C code.

  * bsd --- Also known as ``Allman style'' after Eric Allman.

  * whitesmith --- Popularized by the examples that came with Whitesmiths C, an early commercial C compiler.

  * stroustrup --- The classic Stroustrup style for C++ code.

  * ellemtel --- Popular C++ coding standards as defined by ``Programming in C++, Rules and Recommendations'', Erik Nyquist and Mats Henricson, Ellemtel  (This document is ftp'able from euagate.eua.ericsson.se).

  * linux --- C coding standard for Linux development.

  * python --- C coding standard for Python extension modules (Python is a high level scripting language with a C/C++ foreign function interface.  For more information, see <http://www.python.org/>.).

  * java --- The style for editing Java code.  Note that this style is automatically installed when you enter java-mode.

If you'd like to experiment with these built-in styles you can simply type the following in a CC Mode buffer:

     C-c . STYLE-NAME RET

C-c . runs the command c-set-style.  Note that all style names are case insensitive, even the ones you define.

Setting a style in this way does not automatically re-indent your file.  For commands that you can use to view the effect of your changes, see Commands.

Once you find a built-in style you like, you can make the change permanent by adding some lisp to your .emacs file.  Let's say for example that you want to use the ellemtel style in all your files.  You would add this:

     (defun my-c-mode-common-hook ()
       ;; use Ellemtel style for all C like languages
       (c-set-style "ellemtel")
       ;; other customizations can go here
       )
     (add-hook 'c-mode-common-hook 'my-c-mode-common-hook)

There is one other special style you can use, called cc-mode style.  This style is special because all other styles implicitly inherit from it; in other words, whenever you set a style, cc-mode is applied before the one you selected.  This means your style need only define the differences between it and cc-mode style.

Note you should never change any of the default styles. Instead, it's better to add a new style using c-add-style (see Adding Styles).  This is especially true for cc-mode and java styles.

Note that for BOCM compatibility, gnu is the default style, and any non-style based customizations you make (i.e. in c-mode-common-hook in your .emacs file) will be based on gnu style unless you do a c-set-style as the first thing in your hook.  The variable c-indentation-style always contains the buffer's current style name, as a string.

Adding Styles
-------------

If none of the built-in styles is appropriate, you'll probably want to add a new style definition.  Styles are kept in the c-style-alist variable, but you should never modify this variable directly.  Instead, CC Mode provides the function c-add-style that you can use to easily add new styles or change existing styles.  This function takes two arguments, a STYLENAME string, and an association list DESCRIPTION of style customizations.  If STYLENAME is not already in c-style-alist, the new style is added, otherwise the style is changed to the new DESCRIPTION. This function also takes an optional third argument, which if non-nil, automatically applies the new style to the current buffer.

The sample .emacs file provides a concrete example of how a new style can be added and automatically set.  See Sample .emacs File.

File Styles
-----------

The Emacs manual describes how you can customize certain variables on a per-file basis by including a Local Variable block at the end of the file.  So far, you've only seen a functional interface to CC Mode, which is highly inconvenient for use in a Local Variable block.  CC Mode provides two variables that make it easier for you to customize your style on a per-file basis.

The variable c-file-style can be set to a style name string. When the file is visited, CC Mode will automatically set the file's style to this style using c-set-style.

Another variable, c-file-offsets, takes an association list similar to what is allowed in c-offsets-alist.  When the file is visited, CC Mode will automatically institute these offets using c-set-offset.

Note that file style settings (i.e. c-file-style) are applied before file offset settings (i.e. c-file-offsets) (File styles have only been supported since XEmacs 19.12 and Emacs 19.29. They work via the standard Emacs hook variable hack-local-variables-hook.  Older Emacsen lack this hook, so file styles can't be used with them.).

Advanced Customizations
=======================

For most users, CC Mode will support their coding styles with very little need for more advanced customizations.  Usually, one of the standard styles defined in c-style-alist will do the trick.  At most, perhaps one of the syntactic symbol offsets will need to be tweaked slightly, or maybe c-basic-offset will need to be changed.  However, some styles require a more flexible framework for customization, and one of the real strengths of CC Mode is that the syntactic analysis model provides just such a framework. This allows you to implement custom indentation calculations for situations not handled by the mode directly.

Note that the style controlling variables can either have global values, or can be buffer local (e.g. different in every buffer).  If all the C files you edit tend to have the same style, you might want to keep the variables global.  If you tend to edit files with many different styles, you will have to make the variables buffer local.  The variable c-style-variables-are-local-p controls this.

When c-style-variables-are-local-p is non-nil, then the style variables will have a different settable value for each buffer, otherwise all buffers will share the same values.  This variable only takes effect when CC Mode is loaded into your Emacs session.  By default (for backwards compatibility reasons), its value is t. Note that once the variables are made buffer local, they will retain this property for the remainder of the current Emacs session.  To change this behavior, set c-style-variables-are-local-p to nil before you load cc-mode.el.

Custom Indentation Functions
----------------------------

The most flexible way to customize CC Mode is by writing custom
indentation functions and associating them with specific syntactic symbols (see Syntactic Symbols).  CC Mode itself uses custom indentation functions to provide more sophisticated indentation, for example when lining up C++ stream operator blocks:

     1: void main(int argc, char**)
     2: {
     3:   cout << "There were "
     4:     << argc
     5:     << "arguments passed to the program"
     6:     << endl;
     7: }

In this example, lines 4 through 6 are assigned the stream-op syntactic symbol.  Here, stream-op has an offset of +, and with a c-basic-offset of 2, you can see that lines 4 through 6 are simply indented two spaces to the right of line 3.  But perhaps we'd like CC Mode to be a little more intelligent so that it lines up all the << symbols in lines 3 through 6.  To do this, we have to write a custom indentation function which finds the column of first stream operator on the first line of the statement.  Here is the lisp code (from the cc-mode.el source file) that implements this:

     (defun c-lineup-streamop (langelem)
       ;; lineup stream operators
       (save-excursion
         (let* ((relpos (cdr langelem))
                (curcol (progn (goto-char relpos)
                               (current-column))))
           (re-search-forward "<<\\|>>" (c-point 'eol) 'move)
           (goto-char (match-beginning 0))
           (- (current-column) curcol))))

Custom indent functions take a single argument, which is a syntactic component cons cell (see Syntactic Analysis).  The function returns an integer offset value that will be added to the running total indentation for the line.  Note that what actually gets returned is the difference between the column that the first stream operator is on, and the column of the buffer relative position passed in the function's argument.  Remember that CC Mode automatically adds in the column of the component's relative buffer position and we don't want that value added into the final total twice.

Now, to associate the function c-lineup-streamop with the stream-op syntactic symbol, we can add something like the following to our c++-mode-hook (It probably makes more sense to add this to c++-mode-hook than c-mode-common-hook since stream operators are only relevent for C++.):

     (c-set-offset 'stream-op 'c-lineup-streamop)

Now the function looks like this after re-indenting (using C-c C-q):

     1: void main(int argc, char**)
     2: {
     3:   cout << "There were "
     4:        << argc
     5:        << "arguments passed to the program"
     6:        << endl;
     7: }

Custom indentation functions can be as simple or as complex as you like, and any syntactic symbol that appears in c-offsets-alist can have a custom indentation function associated with it.  CC Mode comes with several standard custom indentation functions, not all of which are used by the default styles.

  * c-lineup-arglist --- lines up function argument lines under the argument on the previous line.

  * c-lineup-arglist-intro-after-paren --- similar to c-lineup-arglist, but works for argument lists that begin with an open parenthesis followed by a newline.

  * c-lineup-arglist-close-under-paren --- set your arglist-close syntactic symbol to this line-up function so that parentheses that close argument lists will line up under the parenthesis that opened the argument list.

  * c-lineup-streamop --- lines up C++ stream operators (e.g. << and >>).

  * c-lineup-multi-inher --- lines up multiple inheritance lines.

  * c-lineup-C-comments --- lines up C block comment continuation lines.

  * c-lineup-comment --- implements the old comment line up behavior specified by the variable c-comment-only-line-offset.

  * c-lineup-runin-statements --- lines up statements for coding standards which place the first statement in a block on the same line as the block opening brace.

  * c-lineup-math --- lines up math statement-cont lines under the previous line after the equals sign.

  * c-lineup-ObjC-method-call --- for Objective-C code, lines up selector arguments just after the message receiver.

  * c-lineup-ObjC-method-args --- for Objective-C code, lines up the colons that separate arguments by aligning colons vertically.

  * c-lineup-ObjC-method-args-2 --- similar to c-lineup-ObjC-method-args but lines up the colon on the current line with the colon on the previous line.

Custom Brace and Colon Hanging
------------------------------

Syntactic symbols aren't the only place where you can customize CC Mode with the lisp equivalent of callback functions.  Brace ``hanginess'' can also be determined by custom functions associated with syntactic symbols on the c-hanging-braces-alist variable. Remember that ACTION's are typically a list containing some combination of the symbols before and after (see Hanging Braces).  However, an ACTION can also be a function symbol which gets called when a brace matching that syntactic symbol is typed.

These ACTION functions are called with two arguments: the syntactic symbol for the brace, and the buffer position at which the brace was inserted.  The ACTION function is expected to return a list containing some combination of before and after.  The function can also return nil.  This return value has the normal brace hanging semantics.

As an example, CC Mode itself uses this feature to dynamically determine the hanginess of braces which close ``do-while'' constructs:

     void do_list( int count, char** atleast_one_string )
     {
         int i=0;
         do {
             handle_string( atleast_one_string[i] );
             i++;
         } while( i < count );
     }

CC Mode assigns the block-close syntactic symbol to the brace that closes the do construct, and normally we'd like the line that follows a block-close brace to begin on a separate line.  However, with ``do-while'' constructs, we want the while clause to follow the closing brace.  To do this, we associate the block-close symbol with the ACTION function c-snug-do-while:

     (defun c-snug-do-while (syntax pos)
       "Dynamically calculate brace hanginess for do-while statements.
     Using this function, `while' clauses that end a `do-while' block will
     remain on the same line as the brace that closes that block.

     See `c-hanging-braces-alist' for how to utilize this function as an
     ACTION associated with `block-close' syntax."
       (save-excursion
         (let (langelem)
           (if (and (eq syntax 'block-close)
                    (setq langelem (assq 'block-close c-syntactic-context))
                    (progn (goto-char (cdr langelem))
                           (if (= (following-char) ?{)
                               (forward-sexp -1))
                           (looking-at "\\<do\\>[^_]")))
               '(before)
             '(before after)))))

This function simply looks to see if the brace closes a ``do-while'' clause and if so, returns the list (before) indicating that a newline should be inserted before the brace, but not after it. In all other cases, it returns the list (before after) so that the brace appears on a line by itself.

During the call to the brace hanging ACTION function, the variable c-syntactic-context is bound to the full syntactic analysis list.

Note that for symmetry, colon hanginess should be customizable by allowing function symbols as ACTIONs on the c-hanging-colon-alist variable.  Since no use has actually been found for this feature, it isn't currently implemented!

Customizing Semi-colons and Commas
----------------------------------

You can also customize the insertion of newlines after semi-colons and commas, when the auto-newline minor mode is enabled (see Minor Modes).  This is controlled by the variable c-hanging-semi&comma-criteria, which contains a list of functions that are called in the order they appear.  Each function is called with zero arguments, and is expected to return one of the following values:

  * non-nil --- A newline is inserted, and no more functions from the list are called.

  * stop --- No more functions from the list are called, but no newline is inserted.

  * nil --- No determination is made, and the next function in the list is called.

If every function in the list is called without a determination being made, then no newline is added. The default value for this variable is a list containing a single function which inserts newlines only after semi-colons which do not appear inside parenthesis lists (i.e. those that separate for-clause statements).

Here's an example of a criteria function that will prevent newlines from being inserted after semicolons when there is a non-blank following line.  Otherwise, it makes no determination.  To use, add this to the front of the c-hanging-semi&comma-criteria list.

     (defun my-semicolon-criteria ()
       (save-excursion
         (if (and (= last-command-char ?\;)
                  (zerop (forward-line 1))
                  (not (looking-at "^[ \t]*$")))
             'stop
           nil)))

Other Special Indentations
--------------------------

In gnu style (see Built-in Styles), a minimum indentation is imposed on lines inside top-level constructs.  This minimum indentation is controlled by the variable c-label-minimum-indentation.  The default value for this variable is 1.

One other customization variable is available in CC Mode: c-special-indent-hook.  This is a standard hook variable that is called after every line is indented by CC Mode.  You can use it to do any special indentation or line adjustments your style dictates, such as adding extra indentation to constructors or destructor declarations in a class definition, etc.  Note however, that you should not change point or mark inside your c-special-indent-hook functions (i.e. you'll probably want to wrap your function in a save-excursion).

Setting c-special-indent-hook in your style definition is handled slightly differently than other variables.  In your style definition, you should set the value for c-special-indent-hook to a function or list of functions, which will be appended to c-special-indent-hook using add-hook. That way, the current setting for the buffer local value of c-special-indent-hook won't be overridden.

Syntactic Symbols
*****************

Here is a complete list of the recognized syntactic symbols as described in the c-offsets-alist variable, along with a brief description. More detailed descriptions follow below.

  * string --- inside multi-line string

  * c --- inside a multi-line C style block comment

  * defun-open --- brace that opens a function definition

  * defun-close --- brace that closes a function definition

  * defun-block-intro --- the first line in a top-level defun

  * class-open --- brace that opens a class definition

  * class-close --- brace that closes a class definition

  * inline-open --- brace that opens an in-class inline method

  * inline-close --- brace that closes an in-class inline method

  * func-decl-cont --- the nether region between a function declaration's argument list and the defun opening brace.  In C++ and Java, this can include the throws clauses of a method declaration.

  * knr-argdecl-intro --- first line of a K&R C argument declaration

  * knr-argdecl --- subsequent lines in a K&R C argument declaration

  * topmost-intro --- the first line in a topmost definition

  * topmost-intro-cont --- topmost definition continuation lines

  * member-init-intro --- first line in a member initialization list

  * member-init-cont --- subsequent member initialization list lines

  * inher-intro --- first line of a multiple inheritance list

  * inher-cont --- subsequent multiple inheritance lines

  * block-open --- statement block open brace

  * block-close --- statement block close brace

  * brace-list-open --- open brace of an enum or static array list

  * brace-list-close --- close brace of an enum or static array list

  * brace-list-intro --- first line in an enum or static array list

  * brace-list-entry --- subsequent lines in an enum or static array list

  * statement --- a C statement

  * statement-cont --- a continuation of a C statement

  * statement-block-intro --- the first line in a new statement block

  * statement-case-intro --- the first line in a case `block'

  * statement-case-open --- the first line in a case block starting with brace

  * substatement --- the first line after a conditional

  * substatement-open --- the brace that opens a substatement block

  * case-label --- a case or default label

  * access-label --- C++ access control label

  * label --- any non-special C label

  * do-while-closure --- the `while' that ends a do-while construct

  * else-clause --- the `else' of an if-else construct

  * comment-intro --- a line containing only a comment introduction

  * arglist-intro --- the first line in an argument list

  * arglist-cont --- subsequent argument list lines when no arguments follow on the same line as the the arglist opening paren

  * arglist-cont-nonempty --- subsequent argument list lines when at least one argument follows on the same line as the arglist opening paren

  * arglist-close --- the solo close paren of an argument list

  * stream-op --- lines continuing a stream operator

  * inclass --- the line is nested inside a class definition

  * cpp-macro --- the start of a cpp macro

  * friend --- a C++ friend declaration

  * objc-method-intro --- the first line of an Objective-C method definition

  * objc-method-args-cont --- lines continuing an Objective-C method definition

  * objc-method-call-cont --- lines continuing an Objective-C method call

  * extern-lang-open --- brace that opens an external language block

  * extern-lang-close --- brace that closes an external language block

  * inextern-lang --- analogous to `inclass' syntactic symbol, but for extern blocks.

Most syntactic symbol names follow a general naming convention.  When a line begins with an open or close brace, the syntactic symbol will contain the suffix -open or -close respectively.

Usually, a distinction is made between the first line that introduces a construct and lines that continue a construct, and the syntactic symbols that represent these lines will contain the suffix -intro or -cont respectively.  As a sub-classification of this scheme, a line which is the first of a particular brace block construct will contain the suffix -block-intro.

Let's look at some examples to understand how this works.  Remember that you can check the syntax of any line by using C-c C-s.

       1: void
       2: swap( int& a, int& b )
       3: {
       4:     int tmp = a;
       5:     a = b;
       6:     b = tmp;
       7:     int ignored =
       8:         a + b;
       9: }

Line 1 shows a topmost-intro since it is the first line that introduces a top-level construct.  Line 2 is a continuation of the top-level construct introduction so it has the syntax topmost-intro-cont.  Line 3 shows a defun-open since it is the brace that opens a top-level function definition.  Line 9 is a defun-close since it contains the brace that closes the top-level function definition.  Line 4 is a defun-block-intro, i.e. it is the first line of a brace-block, which happens to be enclosed in a top-level function definition.

Lines 5, 6, and 7 are all given statement syntax since there isn't much special about them.  Note however that line 8 is given statement-cont syntax since it continues the statement begun on the previous line.

Here's another example, which illustrates some C++ class syntactic symbols:

        1: class Bass
        2:     : public Guitar,
        3:       public Amplifiable
        4: {
        5: public:
        6:     Bass()
        7:         : eString( new BassString( 0.105 )),
        8:           aString( new BassString( 0.085 )),
        9:           dString( new BassString( 0.065 )),
       10:           gString( new BassString( 0.045 ))
       11:     {
       12:         eString.tune( 'E' );
       13:         aString.tune( 'A' );
       14:         dString.tune( 'D' );
       15:         gString.tune( 'G' );
       16:     }
       17:     friend class Luthier;
       18: }

As in the previous example, line 1 has the topmost-intro syntax. Here however, the brace that opens a C++ class definition on line 4 is assigned the class-open syntax.  Note that in C++, classes, structs, and unions are essentially equivalent syntactically (and are very similar semantically), so replacing the class keyword in the example above with struct or union would still result in a syntax of class-open for line 4  (This is the case even for C and Objective-C.  For consistency, structs in all supported languages are syntactically equivalent to classes.  Note however that the keyword class is meaningless in C and Objective-C.). Similarly, line 18 is assigned class-close syntax.

Line 2 introduces the inheritance list for the class so it is assigned the inher-intro syntax, and line 3, which continues the inheritance list is given inher-cont syntax.

Hitting C-c C-s on line 5 shows the following analysis:

     ((inclass . 1) (access-label . 67))

The primary syntactic symbol for this line is access-label as this a label keyword that specifies access protection in C++.  However, because this line is also a top-level construct inside a class definition, the analysis actually shows two syntactic symbols.  The other syntactic symbol assigned to this line is inclass. Similarly, line 6 is given both inclass and topmost-intro syntax:

     ((inclass . 58) (topmost-intro . 60))

Line 7 introduces a C++ member initialization list and as such is given member-init-intro syntax.  Note that in this case it is not assigned inclass since this is not considered a top-level construct.  Lines 8 through 10 are all assigned member-init-cont since they continue the member initialization list started on line 7.

But the line 11's analysis is a bit more complicated:

     ((inclass . 1) (inline-open))

This line is assigned a syntax of both inline-open and inclass because it opens an in-class C++ inline method definition.  This is distinct from, but related to, the C++ notion of an inline function in that its definition occurs inside an enclosing class definition, which in C++ implies that the function should be inlined. For example, if the definition of the Bass constructor appeared outside the class definition, line 11 would be given the defun-open syntax, even if the keyword inline appeared before the method name, as in:

     class Bass
         : public Guitar,
           public Amplifiable
     {
     public:
         Bass();
     }

     inline
     Bass::Bass()
         : eString( new BassString( 0.105 )),
           aString( new BassString( 0.085 )),
           dString( new BassString( 0.065 )),
           gString( new BassString( 0.045 ))
     {
         eString.tune( 'E' );
         aString.tune( 'A' );
         dString.tune( 'D' );
         gString.tune( 'G' );
     }

Returning to the previous example, line 16 is given inline-close syntax, while line 12 is given defun-block-open syntax, and lines 13 through 15 are all given statement syntax.  Line 17 is interesting in that it's syntactic analysis list contains three elements:

     ((friend) (inclass . 58) (topmost-intro . 380))

The friend syntactic symbol is a modifier that typically does not have a relative buffer position.

Here is another (totally contrived) example which illustrates how syntax is assigned to various conditional constructs:

        1: void spam( int index )
        2: {
        3:     for( int i=0; i<index; i++ )
        4:     {
        5:         if( i == 10 )
        6:         {
        7:             do_something_special();
        8:         }
        9:         else
       10:             do_something( i );
       11:     }
       12:     do {
       13:         another_thing( i-- );
       14:     }
       15:     while( i > 0 );
       16: }

Only the lines that illustrate new syntactic symbols will be discussed.

Line 4 has a brace which opens a conditional's substatement block.  It is thus assigned substatement-open syntax, and since line 5 is the first line in the substatement block, it is assigned substatement-block-intro syntax.  Lines 6 and 7 are assigned similar syntax.  Line 8 contains the brace that closes the inner substatement block.  It is given the syntax block-close, as are lines 11 and 14.

Line 9 is a little different --- since it contains the keyword else matching the if statement introduced on line 5, it is given the else-clause syntax.  Note also that line 10 is slightly different too.  Because else is considered a conditional introducing keyword  (The list of conditional keywords are (in C, C++, Objective-C, and Java): for, if, do, else, while, and switch.  C++ and Java have two additional conditional keywords: try and catch.  Java also has the finally and synchronized keywords.), and because the following substatement is not a brace block, line 10 is assigned the substatement syntax.

One other difference is seen on line 15.  The while construct that closes a do conditional is given the special syntax do-while-closure if it appears on a line by itself.  Note that if the while appeared on the same line as the preceding close brace, that line would have been assigned block-close syntax instead.

Switch statements have their own set of syntactic symbols.  Here's an example:

        1: void spam( enum Ingredient i )
        2: {
        3:     switch( i ) {
        4:     case Ham:
        5:         be_a_pig();
        6:         break;
        7:     case Salt:
        8:         drink_some_water();
        9:         break;
       10:     default:
       11:         {
       12:             what_is_it();
       13:             break;
       14:         }
       15:     }
       14: }

Here, lines 4, 7, and 10 are all assigned case-label syntax, while lines 5 and 8 are assigned statement-case-intro.  Line 11 is treated slightly differently since it contains a brace that opens a block --- it is given statement-case-open syntax.

There are a set of syntactic symbols that are used to recognize constructs inside of brace lists.  A brace list is defined as an enum or aggregate initializer list, such as might statically initialize an array of structs.  For example:

       1: static char* ingredients[] =
       2: {
       3:     "Ham",
       4:     "Salt",
       5:     NULL
       6: }

Following convention, line 2 in this example is assigned brace-list-open syntax, and line 3 is assigned brace-list-intro syntax.  Likewise, line 6 is assigned brace-list-close syntax.  Lines 4 and 5 however, are assigned brace-list-entry syntax, as would all subsequent lines in this initializer list.

External language definition blocks also have their own syntactic symbols.  In this example:

        1: extern "C"
        2: {
        3:     int thing_one( int );
        4:     int thing_two( double );
        5: }

line 2 is given the extern-lang-open syntax while line 5 is given the extern-lang-close syntax.  The analysis for line 3 yields: ((inextern-lang) (topmost-intro . 14)), where inextern-lang is a modifier similar in purpose to inclass.

A number of syntactic symbols are associated with parenthesis lists, a.k.a argument lists, as found in function declarations and function calls.  This example illustrates these:

        1: void a_function( int line1,
        2:                  int line2 );
        3:
        4: void a_longer_function(
        5:     int line1,
        6:     int line2
        7:     );
        8:
        9: void call_them( int line1, int line2 )
       10: {
       11:     a_function(
       12:         line1,
       13:         line2
       14:         );
       15:
       16:     a_longer_function( line1,
       17:                        line2 );
       18: }

Lines 5 and 12 are assigned arglist-intro syntax since they are the first line following the open parenthesis, and lines 7 and 14 are assigned arglist-close syntax since they contain the parenthesis that closes the argument list.

Lines that continue argument lists can be assigned one of two syntactic symbols.  For example, Lines 2 and 17 are assigned arglist-cont-nonempty syntax.  What this means is that they continue an argument list, but that the line containing the parenthesis that opens the list is not empty following the open parenthesis.  Contrast this against lines 6 and 13 which are assigned arglist-cont syntax.  This is because the parenthesis that opens their argument lists is the last character on that line.

Note that there is no arglist-open syntax.  This is because any parenthesis that opens an argument list, appearing on a separate line, is assigned the statement-cont syntax instead.

A few miscellaneous syntactic symbols that haven't been previously covered are illustrated by this C++ example:

        1: void Bass::play( int volume )
        2: const
        3: {
        4:     /* this line starts a multi-line
        5:      * comment.  This line should get `c' syntax */
        6:
        7:     char* a_multiline_string = "This line starts a multi-line \
        8: string.  This line should get `string' syntax.";
        9:
       10:   note:
       11:     {
       12: #ifdef LOCK
       13:         Lock acquire();
       14: #endif // LOCK
       15:         slap_pop();
       16:         cout << "I played "
       17:              << "a note\n";
       18:     }
       19: }

The lines to note in this example include:

  * line 2, assigned the func-decl-cont syntax;

  * line 4, assigned both defun-block-intro and comment-intro syntax;

  * line 5, assigned c syntax;

  * line 6 which, even though it contains nothing but whitespace, is assigned defun-block-intro.  Note that the appearance of the comment on lines 4 and 5 do not cause line 6 to be assigned statement syntax because comments are considered to be syntactic whitespace, which are ignored when analyzing code;

  * line 8, assigned string syntax;

  * line 10, assigned label syntax;

  * line 11, assigned block-open syntax;

  * lines 12 and 14, assigned cpp-macro syntax;

  * line 17, assigned stream-op syntax.

In Objective-C buffers, there are three additional syntactic symbols assigned to various message calling constructs.  Here's an example illustrating these:

       1: - (void)setDelegate:anObject
       2:           withStuff:stuff
       3: {
       4:     [delegate masterWillRebind:self
       5:               toDelegate:anObject
       6:               withExtraStuff:stuff];
       7: }

Here, line 1 is assigned objc-method-intro syntax, and line 2 is assigned objc-method-args-cont syntax.  Lines 5 and 6 are both assigned objc-method-call-cont syntax.

Two other syntactic symbols can appear in old style, non-prototyped C code  (a.k.a. K&R C, or Kernighan & Ritchie C):

       1: int add_three_integers(a, b, c)
       2:      int a;
       3:      int b;
       4:      int c;
       5: {
       6:     return a + b + c;
       7: }

Here, line 2 is the first line in an argument declaration list and so is given the knr-argdecl-intro syntactic symbol.  Subsequent lines (i.e. lines 3 and 4 in this example), are given knr-argdecl syntax.

Performance Issues
******************

C and it's derivative languages are highly complex creatures.  Often, ambiguous code situations arise that require CC Mode to scan large portions of the buffer to determine syntactic context.  Such pathological code (such as the output of lex(1)!) can cause CC Mode to perform fairly badly. This section identifies some of the coding styles to watch out for, and suggests some workarounds that you can use to improve performance.

Because CC Mode has to scan the buffer backwards from the current insertion point, and because C's syntax is fairly difficult to parse in the backwards direction, CC Mode often tries to find the nearest position higher up in the buffer from which to begin a forward scan. The farther this position is from the current insertion point, the slower the mode gets.  Some coding styles can even force CC Mode to scan from the beginning of the buffer!

One of the simplest things you can do to reduce scan time, is make sure any brace that opens a top-level block construct always appears in the leftmost column.  This is actually an Emacs constraint, as embodied in the beginning-of-defun function which CC Mode uses heavily.  If you insist on hanging top-level open braces on the right side of the line, then you should set the variable defun-prompt-regexp to something reasonable  (Note that this variable is only defined in Emacs 19.), however that ``something reasonable'' is difficult to define, so CC Mode doesn't do it for you.

A special note about defun-prompt-regexp in Java mode: while much of the early sample Java code seems to encourage a style where the brace that opens a class is hung on the right side of the line, this is not a good style to pursue in Emacs.  CC Mode comes with a variable c-Java-defun-prompt-regexp which tries to define a regular expression usable for this style, but there are problems with it.  In some cases it can cause beginning-of-defun to hang (This has been observed in Emacs 19.34 and XEmacs 19.15.).  For this reason, it is not used by default, but if you feel adventurous, you can set defun-prompt-regexp to it in your mode hook.  In any event, setting and rely on defun-prompt-regexp will definitely slow things down!

You will probably notice pathological behavior from CC Mode when working in files containing large amounts of cpp macros.  This is because CC Mode cannot quickly skip backwards over these lines.

Previous versions of CC Mode had potential performance problems when recognizing K&R style function argument declarations.  This was because there are ambiguities in the C syntax when K&R style argument lists are used (It is hard to distinguish them from top-level
declarations.).  CC Mode has adopted BOCM's convention for limiting the search: it assumes that argdecls are indented at least one space, and that the function headers are not indented at all.  With current versions of CC Mode, user customization of c-recognize-knr-p is deprecated.  Just don't put argdecls in column zero!

You might want to investigate the speed-ups contained in the file cc-lobotomy.el, which is part of the CC Mode distribution. As mentioned previous, CC Mode always trades accuracy for speed, however it is recognized that sometimes you need speed and can sacrifice some accuracy in indentation.  The file cc-lobotomy.el contains hacks that will ``dumb down'' CC Mode in some specific ways, making that trade-off of speed for accuracy.  I won't go into details of its use here; you should read the comments at the top of the file, and look at the variable cc-lobotomy-pith-list for details.

Frequently Asked Questions
**************************

     Q. How do I re-indent the whole file?

     A. Visit the file and hit C-x h to mark the whole buffer. Then hit ESC C-\.

     Q. How do I re-indent the entire function? ESC C-x doesn't work.

     A. ESC C-x is reserved for future Emacs use. To re-indent the entire function hit C-c C-q.

     Q. How do I re-indent the current block?

     A. First move to the brace which opens the block with ESC C-u, then re-indent that expression with ESC C-q.

     Q. Why doesn't the RET key indent the line to where the new text should go after inserting the newline?

     A. Emacs' convention is that RET just adds a newline, and that LFD adds a newline and indents it.  You can make RET do this too by adding this to your c-mode-common-hook (see the sample .emacs file Sample .emacs File):

          (define-key c-mode-map "\C-m" 'newline-and-indent)

     This is a very common question.  If you want this to be the default behavior, don't lobby me, lobby RMS!  :-)

     Q. I put (c-set-offset 'substatement-open 0) in my .emacs file but I get an error saying that c-set-offset's function definition is void.

     A. This means that CC Mode wasn't loaded into your Emacs session by the time the c-set-offset call was reached, mostly likely because CC Mode is being autoloaded.  Instead of putting the c-set-offset line in your top-level .emacs file, put it in your c-mode-common-hook, or simply add the following to the top of your .emacs file:

          (require 'cc-mode)

     See the sample .emacs file Sample .emacs File for details.

     Q. How do I make strings, comments, keywords, and other constructs appear in different colors, or in bold face, etc.?

     A. ``Syntax Colorization'' is an Emacs 19 feature, controlled by font-lock-mode.  It is not part of CC Mode.

     Q. I setq c-basic-offset to 4 in my .emacs file, but why does everything still get indented with only 2 spaces?

     A. It's because c-basic-offset is, by default, a ``buffer local variable'', meaning its value is unique to each buffer. The prefered way to customize this is to change its value in a ``mode hook'' (most likely c-mode-common-hook).  Alternatively you can use setq-default to change its value globally.  Better yet, before you load cc-mode.el, set the variable c-style-variables-are-local-p to nil.  See Advanced Customizations.

Getting the latest CC Mode release
**********************************

CC Mode is now distributed with Emacs 19, XEmacs 19, and XEmacs 20, so you would typically just use the version that comes with your Emacs. These may be slightly out of date due to release schedule skew, so you should always check the canonical site for the latest version.

         World Wide Web:

             http://www.python.org/ftp/emacs/

         Anonymous FTP:

             ftp://ftp.python.org/pub/emacs/

There are many files under these directories; you can pick up the entire distribution (named cc-mode.tar.gz; a gzip'd tar file), or any of the individual files, including PostScript documentation.

If you do not have World Wide Web, or anonymous ftp access, you can get the distribution through an anonymous ftp-to-mail gateway, such as the one run by DEC at:

     ftpmail@decwrl.dec.com

To get CC Mode via email, send the following message in the body of your mail to that address:

     reply <a valid net address back to you>
     connect ftp.python.org
     binary
     uuencode
     chdir pub/emacs
     get cc-mode.tar.gz

or just send the message "help" for more information on ftpmail. Response times will vary with the number of requests in the queue.  I am in no way connected to this service, so I make no claims or guarantees about its availability!

Sample .emacs file
******************

     ;; Here's a sample .emacs file that might help you along the way.  Just
     ;; copy this region and paste it into your .emacs file.  You may want to
     ;; change some of the actual values.

     (defconst my-c-style
       '((c-tab-always-indent        . t)
         (c-comment-only-line-offset . 4)
         (c-hanging-braces-alist     . ((substatement-open after)
                                        (brace-list-open)))
         (c-hanging-colons-alist     . ((member-init-intro before)
                                        (inher-intro)
                                        (case-label after)
                                        (label after)
                                        (access-label after)))
         (c-cleanup-list             . (scope-operator
                                        empty-defun-braces
                                        defun-close-semi))
         (c-offsets-alist            . ((arglist-close . c-lineup-arglist)
                                        (substatement-open . 0)
                                        (case-label        . 4)
                                        (block-open        . 0)
                                        (knr-argdecl-intro . -)))
         (c-echo-syntactic-information-p . t)
         )
       "My C Programming Style")

     ;; Customizations for all of c-mode, c++-mode, and objc-mode
     (defun my-c-mode-common-hook ()
       ;; add my personal style and set it for the current buffer
       (c-add-style "PERSONAL" my-c-style t)
       ;; offset customizations not in my-c-style
       (c-set-offset 'member-init-intro '++)
       ;; other customizations
       (setq tab-width 8
             ;; this will make sure spaces are used instead of tabs
             indent-tabs-mode nil)
       ;; we like auto-newline and hungry-delete
       (c-toggle-auto-hungry-state 1)
       ;; keybindings for all supported languages.  We can put these in
       ;; c-mode-map because c++-mode-map, objc-mode-map, and java-mode-map
       ;; inherit from it.
       (define-key c-mode-map "\C-m" 'newline-and-indent)
       )

     ;; the following only works in Emacs 19
     ;; Emacs 18ers can use (setq c-mode-common-hook 'my-c-mode-common-hook)
     (add-hook 'c-mode-common-hook 'my-c-mode-common-hook)

Limitations and Known Bugs
**************************

  * Multi-line macros are not handled properly.

  * Re-indenting large regions or expressions can be slow.

  * Use with Emacs 18 can be slow and annoying.  You should seriously consider upgrading to Emacs 19.

  * Add-on fill packages may not work as well as CC Mode's built-in filling routines.  I no longer recommend you use filladapt to fill comments.

  * c-indent-exp has not been fully optimized.  It essentially equivalent to hitting TAB (c-indent-command) on every line.  Some information is cached from line to line, but such caching invariable causes inaccuracies in analysis in some bizarre situations.

Mailing Lists and Submitting Bug Reports
****************************************

To report bugs, use the C-c C-b (c-submit-bug-report) command.  This provides vital information I need to reproduce your problem.  Make sure you include a concise, but complete code example. Please try to boil your example down to just the essential code needed to reproduce the problem, and include an exact recipe of steps needed to expose the bug.  Be especially sure to include any code that appears before your bug example, if you think it might affect my ability to reproduce it.

Bug reports are now sent to the following email addresses: cc-mode-help@python.org and bug-gnu-emacs@prep.ai.mit.edu; the latter is mirrored on the Usenet newsgroup gnu.emacs.bug.  You can send other questions, suggestions, and kudos to cc-mode-help@python.org, or help-gnu-emacs@prep.ai.mit.edu which is mirrored on newsgroup gnu.emacs.help.

Command Index
*************

Since all CC Mode commands are prepended with the string c-, each appears under its c-<THING> name and its <THING> (c-) name.

Variable Index
**************

Since all CC Mode variables are prepended with the string c-, each appears under its c-<THING> name and its <THING> (c-) name.