This is ../info/ccmode, produced by makeinfo version 4.0 from
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START-INFO-DIR-ENTRY
* CC mode: (ccmode). The GNU Emacs mode for editing C, C++, Objective-C
and Java code.
END-INFO-DIR-ENTRY
Copyright (C) 1995,96,97,98 Free Software Foundation, Inc.
File: ccmode, Node: Built-in Styles, Next: Adding Styles, Up: 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. This is the default style for all newly
created buffers, but you can change this by setting the variable
`c-default-style'.
* `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 (1).
* `linux' -- C coding standard for Linux development.
* `python' -- C coding standard for Python extension modules(2).
* `java' -- The style for editing Java code. Note that this style is
automatically installed when you enter `java-mode'.
* `user' -- This is a special style for several reasons. First, if
you customize CC Mode by using either the new Custom interface or
by doing `setq''s at the top level of your `.emacs' file, these
settings will be captured in the `user' style. Also, all other
styles implicitly inherit their settings from `user' style. This
means that for any styles you add via `c-add-style' (*note Adding
Styles::) you need only define the differences between your new
style and `user' style.
Note however that `user' style is _not_ the default style. `gnu'
is the default style for all newly created buffers, but you can
change this by setting variable `c-default-style'. Be careful if
you customize CC Mode as described above; since your changes will
be captured in the `user' style, you will also have to change
`c-default-style' to "user" to see the effect of your
customizations.
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 *Note 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)
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.
---------- Footnotes ----------
(1) This document is ftp'able from `euagate.eua.ericsson.se'
(2) Python is a high level scripting language with a C/C++ foreign
function interface. For more information, see
`<http://www.python.org/>'.
File: ccmode, Node: Adding Styles, Next: File Styles, Prev: Built-in Styles, Up: Styles
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. *Note Sample .emacs File::.
File: ccmode, Node: File Styles, Prev: Adding Styles, Up: Styles
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
customization, 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. It works via the standard
Emacs hook variable `hack-local-variables-hook'.
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'). Also, if either
of these are set in a file's local variable section, all the style
variable values are made local to that buffer.
File: ccmode, Node: Advanced Customizations, Prev: Styles, Up: Customizing Indentation
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. By default, its value
is `nil' (i.e. global values). You *must* set this variable before CC
Mode is loaded into your Emacs session, and once the variables are made
buffer local, they cannot be made global again (unless you restart
Emacs of course!)
* Menu:
* Custom Indentation Functions::
* Custom Brace and Colon Hanging::
* Customizing Semi-colons and Commas::
* Other Special Indentations::
File: ccmode, Node: Custom Indentation Functions, Next: Custom Brace and Colon Hanging, Up: Advanced Customizations
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 *Note 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 aligns 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 sample lisp code implementing
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 *Note 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 the column offset
added in 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'(1):
(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-close-paren' -- lines up the closing parenthesis under
its corresponding open parenthesis if that one is followed by code.
Otherwise, if the open parenthesis ends its line, no indentation is
added. Works with any `...-close' symbol.
* `c-lineup-streamop' -- lines up C++ stream operators (e.g. `<<'
and `>>').
* `c-lineup-multi-inher' -- lines up multiple inheritance lines.
* `c-indent-one-line-block' -- adds `c-basic-offset' to the
indentation if the line is a one line block, otherwise 0.
Intended to be used with any opening brace symbol, e.g.
`substatement-open'.
* `c-lineup-C-comments' -- lines up C block comment continuation
lines.
* `c-lineup-comment' -- lines up comment only lines according to the
variable `c-comment-only-line-offset'.
* `c-lineup-runin-statements' -- lines up `statement's for coding
standards which place the first statement in a block on the same
line as the block opening brace(2).
* `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.
* `c-lineup-dont-change' -- this lineup function returns the
indentation of the current line. Think of it as an identity
function for lineups; it is used for `cpp-macro-cont' lines.
---------- Footnotes ----------
(1) 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++.
(2) Run-in style doesn't really work too well. You might need to
write your own custom indentation functions to better support this
style.
File: ccmode, Node: Custom Brace and Colon Hanging, Next: Customizing Semi-colons and Commas, Prev: Custom Indentation Functions, Up: Advanced Customizations
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 *Note Hanging Braces::). However, an
ACTION can also be a function which gets called when a brace matching
that syntactic symbol is entered.
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!
File: ccmode, Node: Customizing Semi-colons and Commas, Next: Other Special Indentations, Prev: Custom Brace and Colon Hanging, Up: Advanced Customizations
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 *Note
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, provided by CC Mode, 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 c-semi&comma-no-newlines-before-nonblanks ()
(save-excursion
(if (and (eq last-command-char ?\;)
(zerop (forward-line 1))
(not (looking-at "^[ \t]*$")))
'stop
nil)))
The default value of `c-hanging-semi&comma-criteria' is a list
containing just the function `c-semi&comma-inside-parenlist', which
suppresses newlines after semicolons inside parenthesis lists (e.g.
`for'-loops). In addition to
`c-semi&comma-no-newlines-before-nonblanks' described above, CC Mode
also comes with the criteria function
`c-semi&comma-no-newlines-for-oneline-inliners', which suppresses
newlines after semicolons inside one-line inline method definitions
(i.e. in C++ or Java).
File: ccmode, Node: Other Special Indentations, Prev: Customizing Semi-colons and Commas, Up: Advanced Customizations
Other Special Indentations
--------------------------
In `gnu' style (see *Note 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.
Normally, the standard Emacs command `M-;' (`indent-for-comment')
will indent comment only lines to `comment-column'. Some users
however, prefer that `M-;' act just like `TAB' for purposes of
indenting comment-only lines; i.e. they want the comments to always
indent as they would for normal code, regardless of whether `TAB' or
`M-;' were used. This behavior is controlled by the variable
`c-indent-comments-syntactically-p'. When `nil' (the default), `M-;'
indents comment-only lines to `comment-column', otherwise, they are
indented just as they would be if `TAB' were typed.
File: ccmode, Node: Syntactic Symbols, Next: Performance Issues, Prev: Customizing Indentation, Up: Top
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 region between a function definition's
argument list and the function opening brace (excluding K&R
argument declarations). In C, you cannot put anything but
whitespace and comments between them; in C++ and Java, `throws'
declarations and other things can appear in this context.
* `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 C preprocessor macro definition
* `cpp-macro-cont' -- subsequent lines of a multi-line C
preprocessor macro definition
* `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
used inside external language blocks (e.g. `extern "C" {').
* `namespace-open' -- brace that opens a C++ namespace block.
* `namespace-close' -- brace that closes a C++ namespace block.
* `innamespace' -- analogous to `inextern-lang' syntactic symbol,
but used inside C++ namespace blocks.
* `template-args-cont' -- C++ template argument list continuations
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, 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 (1). 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.
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. If though, the
definition of the `Bass' constructor appeared outside the class
definition, the construct 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 its 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.
Template definitions introduce yet another syntactic symbol:
1: ThingManager <int,
2: Framework::Callback *,
3: Mutex> framework_callbacks;
Here, line 1 is analyzed as a `topmost-intro', but lines 2 and 3 are
both analyzed as `template-args-cont' lines.
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
(2), 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'.
Similarly, C++ namespace constructs have their own associated
syntactic symbols. In this example:
1: namespace foo
2: {
3: void xxx() {}
4: }
line 2 is given the `namespace-open' syntax, while line 4 is given the
`namespace-close' syntax. The analysis for line 3 yields:
`((innamespace) (topmost-intro . 17))', where `innamespace' is a
modifier similar in purpose to `inextern-lang' and `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.
Multi-line C preprocessor macros are now (somewhat) supported. At
least CC Mode now recognizes the fact that it is inside a multi-line
macro, and it properly skips such macros as syntactic whitespace. In
this example:
1: #define LIST_LOOP(cons, listp) \
2: for (cons = listp; !NILP (cons); cons = XCDR (cons)) \
3: if (!CONSP (cons)) \
4: signal_error ("Invalid list format", listp); \
5: else
line 1 is given the syntactic symbol `cpp-macro'. This first line of a
macro is always given this symbol. The second and subsequent lines
(e.g. lines 2 through 5) are given the `cpp-macro-cont' syntactic
symbol, with a relative buffer position pointing to the `#' which
starts the macro definition.
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 (3):
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.
---------- Footnotes ----------
(1) 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.
(2) 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.
(3) a.k.a. K&R C, or Kernighan & Ritchie C
File: ccmode, Node: Performance Issues, Next: Frequently Asked Questions, Prev: Syntactic Symbols, Up: Top
Performance Issues
******************
C and its 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(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 for every line of code!
One of the simplest things you can do to reduce scan time, is make
sure any brace that opens a top-level construct(2) 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 might want to set the variable `defun-prompt-regexp' to
something reasonable (3), 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(4). 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 C preprocessor macros.
This is because Emacs cannot skip backwards over these lines as quickly
as it can comment.
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(5). 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 comes as part of the CC Mode distribution, but
is completely unsupported. As mentioned previous, CC Mode always
trades speed for accuracy, 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 accurancy for speed. 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.
---------- Footnotes ----------
(1) such as the output of `lex(1)'!
(2) e.g. a function in C, or outermost class definition in C++ or
Java.
(3) Note that this variable is only defined in Emacs 19.
(4) This has been observed in Emacs 19.34 and XEmacs 19.15.
(5) It is hard to distinguish them from top-level declarations.
File: ccmode, Node: Frequently Asked Questions, Next: Getting the latest CC Mode release, Prev: Performance Issues, Up: Top
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
`C-j' 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 *Note Sample .emacs File::):
(define-key c-mode-base-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 *Note 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 a standard Emacs feature, controlled
by `font-lock-mode'. It is not part of CC Mode.
*Q.* _`M-a' and `M-e' used to move over entire balanced brace
lists, but now they move into blocks. How do I get the old
behavior back?_
*A.* Use `C-M-f' and `C-M-b' to move over balanced brace blocks.
Use `M-a' and `M-e' to move by statements, which will move into
blocks.
File: ccmode, Node: Getting the latest CC Mode release, Next: Sample .emacs File, Prev: Frequently Asked Questions, Up: Top
Getting the latest CC Mode release
**********************************
CC Mode is now standard with the latest versions of Emacs 19 and
XEmacs 19. It is also the standard for Emacs 20 and XEmacs 20. You
would typically just use the version that comes with your X/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!