# 26 Editing Programs

## 1 26 Editing Programs

This chapter describes Emacs features for facilitating editing programs. Some of the things these features can do are:

• Find or move over top-level definitions (see Defuns).

在顶层定义上查找或移动（see Defuns）

• Apply the usual indentation conventions of the language (see Program Indent).

使用语言的缩进约定（see Program Indent）。

• Balance parentheses (see Parentheses).

平衡括号（see Parentheses）

• Highlight program syntax (see Font Lock).

高亮程序语法（see Font Lock）。

### 1.1 26.1 Major Modes for Programming Languages

Emacs has specialized major modes (see Major Modes) for many programming languages. A programming language mode typically specifies the syntax of expressions, the customary rules for indentation, how to do syntax highlighting for the language, and how to find the beginning or end of a function definition. It often has features for compiling and debugging programs as well. The major mode for each language is named after the language; for instance, the major mode for the C programming language is c-mode.

Emacs 针对很多编程语言都有专门的主模式（see Major Modes）。编程语言模式通常指定了表达式的语法，缩进的习惯规则，如何做语法高亮，如何查找函数定义的开始和结束。它通常有编译和调试方面的特性。每个语言的主模式通常以该语言开头；例如 c 编程语言的主模式是 c-mode。

Emacs has programming language modes for Lisp, Scheme, the Scheme-based DSSSL expression language, Ada, ASM, AWK, C, C++, Fortran, Icon, IDL (CORBA), IDLWAVE, Java, Javascript, Metafont (TeX’s companion for font creation), Modula2, Object Pascal, Objective-C, Octave, Pascal, Perl, Pike, PostScript, Prolog, Python, Ruby, Simula, Tcl, and VHDL. An alternative mode for Perl is called CPerl mode. Modes are also available for the scripting languages of the common GNU and Unix shells, VMS DCL, and MS-DOS/MS-Windows ‘BAT’ files, and for makefiles, DNS master files, and various sorts of configuration files.

Ideally, Emacs should have a major mode for each programming language that you might want to edit. If it doesn’t have a mode for your favorite language, the mode might be implemented in a package not distributed with Emacs (see Packages); or you can contribute one.

In most programming languages, indentation should vary from line to line to illustrate the structure of the program. Therefore, in most programming language modes, typing TAB updates the indentation of the current line (see Program Indent). Furthermore, DEL is usually bound to backward-delete-char-untabify, which deletes backward treating each tab as if it were the equivalent number of spaces, so that you can delete one column of indentation without worrying whether the whitespace consists of spaces or tabs.

Entering a programming language mode runs the custom Lisp functions specified in the hook variable prog-mode-hook, followed by those specified in the mode’s own mode hook (see Major Modes). For instance, entering C mode runs the hooks prog-mode-hook and c-mode-hook. See Hooks, for information about hooks.

Separate manuals are available for the modes for Ada (see Ada Mode in Ada Mode), C/C++/Objective C/Java/Corba IDL/Pike/AWK (see CC Mode in CC Mode), and IDLWAVE (see IDLWAVE in IDLWAVE User Manual).

### 1.2 26.2 Top-Level Definitions, or Defuns

#### 1.2.1 26.2.4 Which Function Mode

The best way to keep a program properly indented is to use Emacs to reindent it as you change it. Emacs has commands to indent either a single line, a specified number of lines, or all of the lines inside a single parenthetical grouping.

See Indentation, for general information about indentation. This section describes indentation features specific to programming language modes.

Emacs also provides a Lisp pretty-printer in the pp package, which reformats Lisp objects with nice-looking indentation.

### 1.3 26.3 Indentation for Programs

The best way to keep a program properly indented is to use Emacs to reindent it as you change it. Emacs has commands to indent either a single line, a specified number of lines, or all of the lines inside a single parenthetical grouping.

See Indentation, for general information about indentation. This section describes indentation features specific to programming language modes.

#### 1.3.1 26.3.1 Basic Program Indentation Commands

• TAB

Adjust indentation of current line (indent-for-tab-command).

调整当前行缩进（indent-for-tab-command）

• RET

Insert a newline, then adjust indentation of following line (newline).

插入新行，然后调整接下来的缩进（newline）。

The basic indentation command is TAB (indent-for-tab-command), which was documented in Indentation. In programming language modes, TAB indents the current line, based on the indentation and syntactic content of the preceding lines; if the region is active, TAB indents each line within the region, not just the current line.

The command RET (newline), which was documented in Inserting Text, does the same as C-j followed by TAB: it inserts a new line, then adjusts the line’s indentation.

RET（newline）命令记录上 Inserting Text 中，和 C-j 后 TAB 做的事情一样：插入新行，然后调整该行的缩进。

When indenting a line that starts within a parenthetical grouping, Emacs usually places the start of the line under the preceding line within the group, or under the text after the parenthesis. If you manually give one of these lines a nonstandard indentation (e.g., for aesthetic purposes), the lines below will follow it.

The indentation commands for most programming language modes assume that a open-parenthesis, open-brace or other opening delimiter at the left margin is the start of a function. If the code you are editing violates this assumption—even if the delimiters occur in strings or comments—you must set open-paren-in-column-0-is-defun-start to nil for indentation to work properly. See Left Margin Paren.

#### 1.3.2 26.3.2 Indenting Several Lines

Sometimes, you may want to reindent several lines of code at a time. One way to do this is to use the mark; when the mark is active and the region is non-empty, TAB indents every line in the region. Alternatively, the command C-M-\ (indent-region) indents every line in the region, whether or not the mark is active (see Indentation Commands).

In addition, Emacs provides the following commands for indenting large chunks of code:

• C-M-q

Reindent all the lines within one parenthetical grouping.

缩进括号分组中的所有行。

• C-u TAB

Shift an entire parenthetical grouping rigidly sideways so that its first line is properly indented.

这样它的第一行能正确缩进。

• M-x indent-code-rigidly

Shift all the lines in the region rigidly sideways, but do not alter lines that start inside comments and strings.

移动区域中的所有行移动到一遍，但是不改变注释和字符串中的行。

To reindent the contents of a single parenthetical grouping, position point before the beginning of the grouping and type C-M-q. This changes the relative indentation within the grouping, without affecting its overall indentation (i.e., the indentation of the line where the grouping starts). The function that C-M-q runs depends on the major mode; it is indent-pp-sexp in Lisp mode, c-indent-exp in C mode, etc. To correct the overall indentation as well, type TAB first.

If you like the relative indentation within a grouping but not the indentation of its first line, move point to that first line and type C-u TAB. In Lisp, C, and some other major modes, TAB with a numeric argument reindents the current line as usual, then reindents by the same amount all the lines in the parenthetical grouping starting on the current line. It is clever, though, and does not alter lines that start inside strings. Neither does it alter C preprocessor lines when in C mode, but it does reindent any continuation lines that may be attached to them.

The command M-x indent-code-rigidly rigidly shifts all the lines in the region sideways, like indent-rigidly does (see Indentation Commands). It doesn’t alter the indentation of lines that start inside a string, unless the region also starts inside that string. The prefix arg specifies the number of columns to indent.

#### 1.3.3 26.3.3 Customizing Lisp Indentation

The indentation pattern for a Lisp expression can depend on the function called by the expression. For each Lisp function, you can choose among several predefined patterns of indentation, or define an arbitrary one with a Lisp program.

Lisp 表达式的缩进模式依赖于该表达式所调用的函数。对于每个 Lisp 函数，可以在一些预定义缩进模式中选择，或者使用 Lisp 程序定义任意一个。

The standard pattern of indentation is as follows: the second line of the expression is indented under the first argument, if that is on the same line as the beginning of the expression; otherwise, the second line is indented underneath the function name. Each following line is indented under the previous line whose nesting depth is the same.

If the variable lisp-indent-offset is non-nil, it overrides the usual indentation pattern for the second line of an expression, so that such lines are always indented lisp-indent-offset more columns than the containing list.

Certain functions override the standard pattern. Functions whose names start with def treat the second lines as the start of a body, by indenting the second line lisp-body-indent additional columns beyond the open-parenthesis that starts the expression.

You can override the standard pattern in various ways for individual functions, according to the lisp-indent-function property of the function name. This is normally done for macro definitions, using the declare construct. See Defining Macros in the Emacs Lisp Reference Manual.

#### 1.3.4 26.3.4 Commands for C Indentation

Here are special features for indentation in C mode and related modes:

C 和相关模式中有一些与缩进相关的特性：

• C-c C-q

Reindent the current top-level function definition or aggregate type declaration (c-indent-defun).

再次缩进当期顶级的函数定义或者聚合类型声明（c-indent-defun）。

• C-M-q

Reindent each line in the balanced expression that follows point (c-indent-exp). A prefix argument inhibits warning messages about invalid syntax.

缩进 point 后面平衡表达式中的每一行（c-indent-exp）。前缀参数阻止和无效语法有关的警告消息。

• TAB

Reindent the current line, and/or in some cases insert a tab character (c-indent-command).

重新缩进当前行，在某些情况下插入制表符（c-indent-command）。

If c-tab-always-indent is t, this command always reindents the current line and does nothing else. This is the default.

如果 c-tab-always-indent 为 t，该命令总是缩进当前行，不做其他事情，这是默认值。

If that variable is nil, this command reindents the current line only if point is at the left margin or in the line’s indentation; otherwise, it inserts a tab (or the equivalent number of spaces, if indent-tabs-mode is nil).

如果该变量为 nil，只有 point 在左边界或者当前行的缩进中时，才会缩进当前行；否则插入一个制表符（如果 indent-tabs-mode 为 nil 插入相同数量的空格符）。

Any other value (not nil or t) means always reindent the line, and also insert a tab if within a comment or a string.

任何其他值（非 nil 或 t）意味着总是重新缩进该行，如果在注释或字符串中的话插入制表符。

To reindent the whole current buffer, type C-x h C-M-\. This first selects the whole buffer as the region, then reindents that region.

To reindent the current block, use C-M-u C-M-q. This moves to the front of the block and then reindents it all.

#### 1.3.5 26.3.5 Customizing C Indentation

C mode and related modes use a flexible mechanism for customizing indentation. C mode indents a source line in two steps: first it classifies the line syntactically according to its contents and context; second, it determines the indentation offset associated by your selected style with the syntactic construct and adds this onto the indentation of the anchor statement.

C 模式和相关模式使用灵活的机制来定制缩进解决机制。C 模式通过两步缩进代码行：首先通过内容和上下文将行进行语法归类；然后，它根据选择的语法构造决定缩进偏移，并将其添加到语句的缩进上。

• C-c . style RET

Select a predefined style style (c-set-style).

选择预定义的风格（c-set-style）。

A style is a named collection of customizations that can be used in C mode and the related modes. Styles in The CC Mode Manual, for a complete description. Emacs comes with several predefined styles, including gnu, k&r, bsd, stroustrup, linux, python, java, whitesmith, ellemtel, and awk. Some of these styles are primarily intended for one language, but any of them can be used with any of the languages supported by these modes. To find out what a style looks like, select it and reindent some code, e.g., by typing C-M-q at the start of a function definition.

To choose a style for the current buffer, use the command C-c .. Specify a style name as an argument (case is not significant). This command affects the current buffer only, and it affects only future invocations of the indentation commands; it does not reindent the code already in the buffer. To reindent the whole buffer in the new style, you can type C-x h C-M-\.

You can also set the variable c-default-style to specify the default style for various major modes. Its value should be either the style’s name (a string) or an alist, in which each element specifies one major mode and which indentation style to use for it. For example,

(setq c-default-style
'((java-mode . "java")
(awk-mode . "awk")
(other . "gnu")))


specifies explicit choices for Java and AWK modes, and the default ‘gnu’ style for the other C-like modes. (These settings are actually the defaults.) This variable takes effect when you select one of the C-like major modes; thus, if you specify a new default style for Java mode, you can make it take effect in an existing Java mode buffer by typing M-x java-mode there.

The gnu style specifies the formatting recommended by the GNU Project for C; it is the default, so as to encourage use of our recommended style.

gnu 风格为 C 使用 GNU Project 推荐的格式；它是默认值，所以鼓励使用推荐的模式。

See Indentation Engine Basics in the CC Mode Manual, and Customizing Indentation in the CC Mode Manual, for more information on customizing indentation for C and related modes, including how to override parts of an existing style and how to define your own styles. 参看 CC Mode Manual 中的 Indentation Engine Basics 和 Customizing Indentation 了解关于为 C 和相关模式定制缩进的更多信息，包括如何改写已有风格的部分，如何定义自己的风格。

As an alternative to specifying a style, you can tell Emacs to guess a style by typing M-x c-guess in a sample code buffer. You can then apply the guessed style to other buffers with M-x c-guess-install. See Guessing the Style in the CC Mode Manual, for details.

### 1.4 26.4 Commands for Editing with Parentheses

This section describes the commands and features that take advantage of the parenthesis structure in a program, or help you keep it balanced.

When talking about these facilities, the term “parenthesis” also includes braces, brackets, or whatever delimiters are defined to match in pairs. The major mode controls which delimiters are significant, through the syntax table (see Syntax Tables in The Emacs Lisp Reference Manual). In Lisp, only parentheses count; in C, these commands apply to braces and brackets too.

You can use M-x check-parens to find any unbalanced parentheses and unbalanced string quotes in the buffer.

#### 1.4.1 26.4.1 Expressions with Balanced Parentheses

Each programming language mode has its own definition of a balanced expression. Balanced expressions typically include individual symbols, numbers, and string constants, as well as pieces of code enclosed in a matching pair of delimiters. The following commands deal with balanced expressions (in Emacs, such expressions are referred to internally as sexps11).

• C-M-f

Move forward over a balanced expression (forward-sexp).

向前移动一个平衡表达式（forward-sexp）。

• C-M-b

Move backward over a balanced expression (backward-sexp).

向后移动一个平衡表达式（backward-sexp）。

• C-M-k

Kill balanced expression forward (kill-sexp).

向前删除一个平衡表达式（kill-sexp）。

• C-M-t

Transpose expressions (transpose-sexps).

交换表达式位置（transpose-sexps）。

• C-M-@
• C-M-SPC

Put mark after following expression (mark-sexp).

在表达式之后设置 mark（mark-sexp）。

To move forward over a balanced expression, use C-M-f (forward-sexp). If the first significant character after point is an opening delimiter (e.g., ‘(’, ‘[’ or ‘{’ in C), this command moves past the matching closing delimiter. If the character begins a symbol, string, or number, the command moves over that.

The command C-M-b (backward-sexp) moves backward over a balanced expression—like C-M-f, but in the reverse direction. If the expression is preceded by any prefix characters (single-quote, backquote and comma, in Lisp), the command moves back over them as well.

C-M-f or C-M-b with an argument repeats that operation the specified number of times; with a negative argument means to move in the opposite direction. In most modes, these two commands move across comments as if they were whitespace. Note that their keys, C-M-f and C-M-b, are analogous to C-f and C-b, which move by characters (see Moving Point), and M-f and M-b, which move by words (see Words).

To kill a whole balanced expression, type C-M-k (kill-sexp). This kills the text that C-M-f would move over.

C-M-t (transpose-sexps) switches the positions of the previous balanced expression and the next one. It is analogous to the C-t command, which transposes characters (see Transpose). An argument to C-M-t serves as a repeat count, moving the previous expression over that many following ones. A negative argument moves the previous balanced expression backwards across those before it. An argument of zero, rather than doing nothing, transposes the balanced expressions ending at or after point and the mark.

C-M-t（transpose-sepx）交换前后平衡表达式的位置。类似交换字符的 c-t 命令（see Transpose）。C-M-t 的参数代表重复次数，将前一个表达式向后移动很多次。负数表示将表达式向前移动。参数 0 表示什么都不做，只是将 mark 和 point 处或其后的平衡表达式的结束位置进行交换。

To operate on balanced expressions with a command which acts on the region, type C-M-SPC (mark-sexp). This sets the mark where C-M-f would move to. While the mark is active, each successive call to this command extends the region by shifting the mark by one expression. Positive or negative numeric arguments move the mark forward or backward by the specified number of expressions. The alias C-M-@ is equivalent to C-M-SPC. See Marking Objects, for more information about this and related commands.

In languages that use infix operators, such as C, it is not possible to recognize all balanced expressions because there can be multiple possibilities at a given position. For example, C mode does not treat ‘foo + bar’ as a single expression, even though it is one C expression; instead, it recognizes ‘foo’ as one expression and ‘bar’ as another, with the ‘+’ as punctuation between them. However, C mode recognizes ‘(foo + bar)’ as a single expression, because of the parentheses.

#### 1.4.2 26.4.2 Moving in the Parenthesis Structure

The following commands move over groupings delimited by parentheses (or whatever else serves as delimiters in the language you are working with). They ignore strings and comments, including any parentheses within them, and also ignore parentheses that are “quoted” with an escape character. These commands are mainly intended for editing programs, but can be useful for editing any text containing parentheses. They are referred to internally as “list” commands because in Lisp these groupings are lists.

These commands assume that the starting point is not inside a string or a comment. If you invoke them from inside a string or comment, the results are unreliable.

• C-M-n

Move forward over a parenthetical group (forward-list).

前进一个括号组（forward-list）

• C-M-p

Move backward over a parenthetical group (backward-list).

后退一个括号组（backword-list）

• C-M-u

Move up in parenthesis structure (backward-up-list).

上移一个括号组（backword-up-list）

• C-M-d

Move down in parenthesis structure (down-list).

下移一个括号组（down-list）

The “list” commands C-M-n (forward-list) and C-M-p (backward-list) move forward or backward over one (or n) parenthetical groupings.

list 命令 C-M-n 和 C-M-p 前移或后移一个（或 n 个）括号组。

C-M-n and C-M-p try to stay at the same level in the parenthesis structure. To move up one (or n) levels, use C-M-u (backward-up-list). C-M-u moves backward up past one unmatched opening delimiter. A positive argument serves as a repeat count; a negative argument reverses the direction of motion, so that the command moves forward and up one or more levels.

C-M-n 和 C-M-p 尝试待在括号结构的统一等级。上移一个（或 n）个等级，使用 C-M-u（backword-up-list）。C-M-u 向后上移一个不匹配的开分隔符。正数参数执行重复次数，负值参数反向执行，所以该命令向前上移一个或更多层级。

To move down in the parenthesis structure, use C-M-d (down-list). In Lisp mode, where ‘(’ is the only opening delimiter, this is nearly the same as searching for a ‘(’. An argument specifies the number of levels to go down.

#### 1.4.3 26.4.3 Matching Parentheses

Emacs has a number of parenthesis matching features, which make it easy to see how and whether parentheses (or other delimiters) match up.

Emacs 有很多括号匹配的特性，这样很容易侃如括号（或其他分隔符）如何匹配以及是否匹配。

Whenever you type a self-inserting character that is a closing delimiter, Emacs briefly indicates the location of the matching opening delimiter, provided that is on the screen. If it is not on the screen, Emacs displays some of the text near it in the echo area. Either way, you can tell which grouping you are closing off. If the opening delimiter and closing delimiter are mismatched—such as in ‘[x)’—a warning message is displayed in the echo area.

Three variables control the display of matching parentheses:

• blink-matching-paren turns the feature on or off: nil disables it, but the default is t to enable it. Set it to jump to make indication work by momentarily moving the cursor to the matching opening delimiter.

• blink-matching-delay says how many seconds to keep indicating the matching opening delimiter. This may be an integer or floating-point number; the default is 1.

• blink-matching-paren-distance specifies how many characters back to search to find the matching opening delimiter. If the match is not found in that distance, Emacs stops scanning and nothing is displayed. The default is 102400.

Show Paren mode, a global minor mode, provides a more powerful kind of automatic matching. Whenever point is before an opening delimiter or after a closing delimiter, both that delimiter and its opposite delimiter are highlighted. To toggle Show Paren mode, type M-x show-paren-mode.

Show Paren 模式，是一个全局辅助模式，提供了更加强大的自动匹配。不论 point 实在开分隔符之前还是关分隔符之后哦，两种分隔符及对应的分隔符都会高亮显示。输入 M-x show-paren-mode 切换该模式。

Electric Pair mode, a global minor mode, provides a way to easily insert matching delimiters. Whenever you insert an opening delimiter, the matching closing delimiter is automatically inserted as well, leaving point between the two. Conversely, when you insert a closing delimiter over an existing one, no inserting takes places and that position is simply skipped over. These variables control additional features of Electric Pair mode:

Electric Pair 模式，是一个全局辅助模式，提供一种可以方便插入匹配分隔符的方法。插入开分隔符的时候也会自耦东插入匹配的关分隔符，将 point 留在两个中间。相反，当关分隔符已经存在继续插入时会直接跳过该位置。控制 Electric Pair 模式附加属性的变量如下：

• electric-pair-preserve-balance, when non-nil, makes the default pairing logic balance out the number of opening and closing delimiters.

electric-pair-preserve-balance，如果非 nil，使用默认的配对逻辑平衡开关分隔符的数量。

• electric-pair-delete-adjacent-pairs, when non-nil, makes backspacing between two adjacent delimiters also automatically delete the closing delimiter.

• electric-pair-open-newline-between-pairs, when non-nil, makes inserting inserting a newline between two adjacent pairs also automatically open and extra newline after point.

electric-pair-open-newline-between-pairs，非 nil 值，在两个相邻配对分隔符之间插入新行会自动在 point 之后打开额外的新行。

• electric-pair-skip-whitespace, when non-nil, causes the minor mode to skip whitespace forward before deciding whether to skip over the closing delimiter.

electric-pair-skip-whitespace，非 nil 时，导致辅助模式在决定是否跳过关分隔符之前向前跳过空白符。

To toggle Electric Pair mode, type M-x electric-pair-mode.

Because comments are such an important part of programming, Emacs provides special commands for editing and inserting comments. It can also do spell checking on comments with Flyspell Prog mode (see Spelling).

Some major modes have special rules for indenting different kinds of comments. For example, in Lisp code, comments starting with two semicolons are indented as if they were lines of code, while those starting with three semicolons are supposed to be aligned to the left margin and are often used for sectioning purposes. Emacs understand these conventions; for instance, typing TAB on a comment line will indent the comment to the appropriate position.

;; This function is just an example.
;;; Here either two or three semicolons are appropriate.
(defun foo (x)
;;;  And now, the first part of the function:
;; The following line adds one.
(1+ x))           ; This line adds one.


#### 1.5.1 26.5.1 Comment Commands

The following commands operate on comments:

• M-;

Insert or realign comment on current line; if the region is active, comment or uncomment the region instead (comment-dwim).

插入或调整当前行的注释；如果激活区域，切换区域的注释状态（comment-dwim）。

• C-u M-;

Kill comment on current line (comment-kill).

删除当前行上的注释（comment-kill）。

• C-x ;

Set comment column (comment-set-column).

设置注释列（comment-set-column）。

• C-M-j
• M-j

Like RET followed by inserting and aligning a comment (comment-indent-new-line). See Multi-Line Comments.

• M-x comment-region
• C-c C-c (in C-like modes)

在区域的所有行添加注释分隔符。

The command to create or align a comment is M-; (comment-dwim). The word “dwim” is an acronym for “Do What I Mean”; it indicates that this command can be used for many different jobs relating to comments, depending on the situation where you use it.

When a region is active (see Mark), M-; either adds comment delimiters to the region, or removes them. If every line in the region is already a comment, it “uncomments” each of those lines by removing their comment delimiters. Otherwise, it adds comment delimiters to enclose the text in the region.

If you supply a prefix argument to M-; when a region is active, that specifies the number of comment delimiters to add or delete. A positive argument n adds n delimiters, while a negative argument -n removes n delimiters.

If the region is not active, and there is no existing comment on the current line, M-; adds a new comment to the current line. If the line is blank (i.e., empty or containing only whitespace characters), the comment is indented to the same position where TAB would indent to (see Basic Indent). If the line is non-blank, the comment is placed after the last non-whitespace character on the line; normally, Emacs tries putting it at the column specified by the variable comment-column (see Options for Comments), but if the line already extends past that column, it puts the comment at some suitable position, usually separated from the non-comment text by at least one space. In each case, Emacs places point after the comment’s starting delimiter, so that you can start typing the comment text right away.

You can also use M-; to align an existing comment. If a line already contains the comment-start string, M-; realigns it to the conventional alignment and moves point after the comment’s starting delimiter. As an exception, comments starting in column 0 are not moved. Even when an existing comment is properly aligned, M-; is still useful for moving directly to the start of the comment text.

C-u M-; (comment-dwim with a prefix argument) kills any comment on the current line, along with the whitespace before it. Since the comment is saved to the kill ring, you can reinsert it on another line by moving to the end of that line, doing C-y, and then M-; to realign the comment. You can achieve the same effect as C-u M-; by typing M-x comment-kill (comment-dwim actually calls comment-kill as a subroutine when it is given a prefix argument).

C-u M-;（带有前置参数的 comment-dwim）会删除当前行上的任何注释及其前面的空白符。移动到另一行结尾后通过 C-y 直接插入保存在 kill 环中的注释，然后 M-;调整注释。输入 M-x comment-kill 可以达到 C-u M-;同样的效果（当 comment-dwim 伴随前缀参数的时候，它实际上将 comment-kill 作为子程序调用）。

The command M-x comment-region is equivalent to calling M-; on an active region, except that it always acts on the region, even if the mark is inactive. In C mode and related modes, this command is bound to C-c C-c. The command M-x uncomment-region uncomments each line in the region; a numeric prefix argument specifies the number of comment delimiters to remove (negative arguments specify the number of comment to delimiters to add).

For C-like modes, you can configure the exact effect of M-; by setting the variables c-indent-comment-alist and c-indent-comments-syntactically-p. For example, on a line ending in a closing brace, M-; puts the comment one space after the brace rather than at comment-column. For full details see Comment Commands in The CC Mode Manual.

#### 1.5.2 26.5.2 Multiple Lines of Comments

If you are typing a comment and wish to continue it to another line, type M-j or C-M-j (comment-indent-new-line). This breaks the current line, and inserts the necessary comment delimiters and indentation to continue the comment.

For languages with closing comment delimiters (e.g., ‘*/’ in C), the exact behavior of M-j depends on the value of the variable comment-multi-line. If the value is nil, the command closes the comment on the old line and starts a new comment on the new line. Otherwise, it opens a new line within the current comment delimiters.

When Auto Fill mode is on, going past the fill column while typing a comment also continues the comment, in the same way as an explicit invocation of M-j.

To turn existing lines into comment lines, use M-; with the region active, or use M-x comment-region as described in the preceding section.

You can configure C Mode such that when you type a ‘/’ at the start of a line in a multi-line block comment, this closes the comment. Enable the comment-close-slash clean-up for this. See Clean-ups in The CC Mode Manual.

#### 1.5.3 26.5.3 Options Controlling Comments

As mentioned in Comment Commands, when the M-j command adds a comment to a line, it tries to place the comment at the column specified by the buffer-local variable comment-column. You can set either the local value or the default value of this buffer-local variable in the usual way (see Locals). Alternatively, you can type C-x ; (comment-set-column) to set the value of comment-column in the current buffer to the column where point is currently located. C-u C-x ; sets the comment column to match the last comment before point in the buffer, and then does a M-; to align the current line’s comment under the previous one.

The comment commands recognize comments based on the regular expression that is the value of the variable comment-start-skip. Make sure this regexp does not match the null string. It may match more than the comment starting delimiter in the strictest sense of the word; for example, in C mode the value of the variable is "\$$//+\\|/\\*+\$$\\s *", which matches extra stars and spaces after the ‘/*’ itself, and accepts C++ style comments also. (Note that ‘\\’ is needed in Lisp syntax to include a ‘\’ in the string, which is needed to deny the first star its special meaning in regexp syntax. See Regexp Backslash.)

When a comment command makes a new comment, it inserts the value of comment-start as an opening comment delimiter. It also inserts the value of comment-end after point, as a closing comment delimiter. For example, in Lisp mode, comment-start is ‘";"’ and comment-end is "" (the empty string). In C mode, comment-start is "* " and comment-end is " *".

The variable comment-padding specifies a string that the commenting commands should insert between the comment delimiter(s) and the comment text. The default, ‘" "’, specifies a single space. Alternatively, the value can be a number, which specifies that number of spaces, or nil, which means no spaces at all.

The variable comment-multi-line controls how M-j and Auto Fill mode continue comments over multiple lines. See Multi-Line Comments.

The variable comment-indent-function should contain a function that will be called to compute the alignment for a newly inserted comment or for aligning an existing comment. It is set differently by various major modes. The function is called with no arguments, but with point at the beginning of the comment, or at the end of a line if a new comment is to be inserted. It should return the column in which the comment ought to start. For example, in Lisp mode, the indent hook function bases its decision on how many semicolons begin an existing comment, and on the code in the preceding lines.

### 1.6 26.6 Documentation Lookup

Emacs provides several features you can use to look up the documentation of functions, variables and commands that you plan to use in your program.

#### 1.6.1 26.6.1 Info Documentation Lookup

For major modes that apply to languages which have documentation in Info, you can use C-h S (info-lookup-symbol) to view the Info documentation for a symbol used in the program. You specify the symbol with the minibuffer; the default is the symbol appearing in the buffer at point. For example, in C mode this looks for the symbol in the C Library Manual. The command only works if the appropriate manual’s Info files are installed.

The major mode determines where to look for documentation for the symbol—which Info files to look in, and which indices to search. You can also use M-x info-lookup-file to look for documentation for a file name.

If you use C-h S in a major mode that does not support it, it asks you to specify the “symbol help mode”. You should enter a command such as c-mode that would select a major mode which C-h S does support.

#### 1.6.2 26.6.2 Man Page Lookup

On Unix, the main form of on-line documentation was the manual page or man page. In the GNU operating system, we aim to replace man pages with better-organized manuals that you can browse with Info (see Misc Help). This process is not finished, so it is still useful to read manual pages.

unix 上，在线文档的主要形式是 manual page 或者 man page。在 GNU 操作系统中，我们目标是使用更有效组织的手册来取代 man pages，这样就可以浏览 Info（参见 Misc Help）。这个过程还没有完成，所以阅读手册也还是有用的。

You can read the man page for an operating system command, library function, or system call, with the M-x man command. This prompts for a topic, with completion (see Completion), and runs the man program to format the corresponding man page. If the system permits, it runs man asynchronously, so that you can keep on editing while the page is being formatted. The result goes in a buffer named Man topic. These buffers use a special major mode, Man mode, that facilitates scrolling and jumping to other manual pages. For details, type C-h m while in a Man mode buffer.

Each man page belongs to one of ten or more sections, each named by a digit or by a digit and a letter. Sometimes there are man pages with the same name in different sections. To read a man page from a specific section, type ‘topic(section)’ or ‘section topic’ when M-x manual-entry prompts for the topic. For example, the man page for the C library function chmod is in section 2, but there is a shell command of the same name, whose man page is in section 1; to view the former, type M-x manual-entry RET chmod(2) RET.

If you do not specify a section, M-x man normally displays only the first man page found. On some systems, the man program accepts a ‘-a’ command-line option, which tells it to display all the man pages for the specified topic. To make use of this, change the value of the variable Man-switches to ‘"-a"’. Then, in the Man mode buffer, you can type M-n and M-p to switch between man pages in different sections. The mode line shows how many manual pages are available.

An alternative way of reading manual pages is the M-x woman command. Unlike M-x man, it does not run any external programs to format and display the man pages; the formatting is done by Emacs, so it works on systems such as MS-Windows where the man program may be unavailable. It prompts for a man page, and displays it in a buffer named *WoMan section topic.

M-x woman computes the completion list for manpages the first time you invoke the command. With a numeric argument, it recomputes this list; this is useful if you add or delete manual pages.

M-x woman 会在第一次调用时计算 manpage 的补全列表。使用数字参数，它会重新计算该列表；如果添加和删除 manual page 会用到这个。

If you type a name of a manual page and M-x woman finds that several manual pages by the same name exist in different sections, it pops up a window with possible candidates asking you to choose one of them.

For more information about setting up and using M-x woman, see the WoMan Info manual, which is distributed with Emacs.

#### 1.6.3 26.6.3 Emacs Lisp Documentation Lookup

When editing Emacs Lisp code, you can use the commands C-h f (describe-function) and C-h v (describe-variable) to view the built-in documentation for the Lisp functions and variables that you want to use. See Name Help.

Eldoc is a buffer-local minor mode that helps with looking up Lisp documentation. When it is enabled, the echo area displays some useful information whenever there is a Lisp function or variable at point; for a function, it shows the argument list, and for a variable it shows the first line of the variable’s documentation string. To toggle Eldoc mode, type M-x eldoc-mode. Eldoc mode can be used with the Emacs Lisp and Lisp Interaction major modes.

Eldoc 是一个 buffer-local 辅助模式，有助于查找 Lisp 文档。当启用后，回显区会显示当前 buffer 中 point 处 Lisp 函数和变量的一些有用信息；函数显示参数列表，变量显示变量文档字符串的第一行。使用 M-x eldoc-mode 切换 Eldoc mode。Eldoc mode 可以嗯好 Emasc Lisp 和 Lisp 交互模式一块使用。

### 1.7 26.7 Hideshow minor mode

Hideshow mode is a buffer-local minor mode that allows you to selectively display portions of a program, which are referred to as blocks. Type M-x hs-minor-mode to toggle this minor mode (see Minor Modes).

Hideshow 模式是 buffer-local 类型的辅助模式，可以有选择的显示程序的一部分，也就是常说的代码块。输入 M-x hs-minor-mode 切换该辅助模式。

When you use Hideshow mode to hide a block, the block disappears from the screen, to be replaced by an ellipsis (three periods in a row). Just what constitutes a block depends on the major mode. In C mode and related modes, blocks are delimited by braces, while in Lisp mode they are delimited by parentheses. Multi-line comments also count as blocks.

Hideshow mode provides the following commands:

Hideshow 模式提供以下命令：

• C-c @ C-h

Hide the current block (hs-hide-block).

• C-c @ C-s

Show the current block (hs-show-block).

• C-c @ C-c

Either hide or show the current block (hs-toggle-hiding).

• S-Mouse-2

Toggle hiding for the block you click on (hs-mouse-toggle-hiding).

• C-c @ C-M-h

Hide all top-level blocks (hs-hide-all).

• C-c @ C-M-s

Show all blocks in the buffer (hs-show-all).

• C-c @ C-l

Hide all blocks n levels below this block (hs-hide-level).

These variables can be used to customize Hideshow mode:

If non-nil, C-c @ C-M-h (hs-hide-all) hides comments too.

• hs-isearch-open

This variable specifies the conditions under which incremental search should unhide a hidden block when matching text occurs within the block. Its value should be either code (unhide only code blocks), comment (unhide only comments), t (unhide both code blocks and comments), or nil (unhide neither code blocks nor comments). The default value is code.

该值说明如果递增搜索过程中如果匹配的文本出现在块中，应该如何显示隐藏的块。它的值应该是 code（只显示代码块），t（代码块和注释都显示），nil（代码块和注释都不显示）。默认值是 code。

### 1.8 26.8 Completion for Symbol Names

Completion is normally done in the minibuffer (see Completion), but you can also complete symbol names in ordinary Emacs buffers.

In programming language modes, type C-M-i or M-TAB to complete the partial symbol before point. On graphical displays, the M-TAB key is usually reserved by the window manager for switching graphical windows, so you should type C-M-i or ESC TAB instead.

In most programming language modes, C-M-i (or M-TAB) invokes the command completion-at-point, which generates its completion list in a flexible way. If Semantic mode is enabled, it tries to use the Semantic parser data for completion (see Semantic). If Semantic mode is not enabled or fails at performing completion, it tries to complete using the selected tags table (see Tags). If in Emacs Lisp mode, it performs completion using the function, variable, or property names defined in the current Emacs session.

In all other respects, in-buffer symbol completion behaves like minibuffer completion. For instance, if Emacs cannot complete to a unique symbol, it displays a list of completion alternatives in another window. See Completion.

In Text mode and related modes, M-TAB completes words based on the spell-checker’s dictionary. See Spelling.

Text 模式或相关模式中，M-TAB 基于拼写检查器字典补全单词。See Spelling。

### 1.9 26.9 MixedCase Words

Some programming styles make use of mixed-case (or “CamelCase”) symbols like ‘unReadableSymbol’. (In the GNU project, we recommend using underscores to separate words within an identifier, rather than using case distinctions.) Emacs has various features to make it easier to deal with such symbols.

Glasses mode is a buffer-local minor mode that makes it easier to read such symbols, by altering how they are displayed. By default, it displays extra underscores between each lower-case letter and the following capital letter. This does not alter the buffer text, only how it is displayed.

Glasses 模式是一个 buffer-local 类型的辅助模式，通过改变这种符号的显示方式可以更容易的读取它们。默认情况下，它在每个小写字母和紧跟的大写字母之间显示额外的下划线。这不会改变 buffer 文本，只是改变显示方式。

To toggle Glasses mode, type M-x glasses-mode (see Minor Modes). When Glasses mode is enabled, the minor mode indicator ‘o^o’ appears in the mode line. For more information about Glasses mode, type C-h P glasses RET.

Subword mode is another buffer-local minor mode. In subword mode, Emacs’s word commands recognize upper case letters in ‘StudlyCapsIdentifiers’ as word boundaries. When Subword mode is enabled, the minor mode indicator ‘,’ appears in the mode line. See also the similar superword-mode (see Misc for Programs).

Subword 模式也是一种 buffer-local 辅助模式。subword 模式中，Emacs 单词命令将大写字母识别为单词边界。启用 subword 模式时，在模式行显示辅助模式指示符‘，’。类似的还有 superword-mode。

### 1.10 26.10 Semantic

Semantic is a package that provides language-aware editing commands based on source code parsers. This section provides a brief description of Semantic; for full details, see Semantic in Semantic.

Semantic 是一个基于源码分析器来提供对语言敏感的编辑命令的包。本节简短描述 Semantic；更多细节参看 Semantic。

Most of the “language aware” features in Emacs, such as Font Lock mode (see Font Lock), rely on “rules of thumb”12 that usually give good results but are never completely exact. In contrast, the parsers used by Semantic have an exact understanding of programming language syntax. This allows Semantic to provide search, navigation, and completion commands that are powerful and precise.

Emacs 中大多数语言敏感的特性，比如 Font Lock 模式（see Font Lock），依赖于经验法则，通常这会给出一个好的结果但不完全准确。相比之下，Semantic 使用的解析器对编程语言语法有准确的理解。这样 Semantic 就能提供搜索、浏览以及强大和精确的补全命令。

To begin using Semantic, type M-x semantic-mode or click on the menu item named ‘Source Code Parsers (Semantic)’ in the ‘Tools’ menu. This enables Semantic mode, a global minor mode.

When Semantic mode is enabled, Emacs automatically attempts to parse each file you visit. Currently, Semantic understands C, C++, Scheme, Javascript, Java, HTML, and Make. Within each parsed buffer, the following commands are available:

• C-c , j

Prompt for the name of a function defined in the current file, and move point there (semantic-complete-jump-local).

提示当前文件中定义个的函数名，并进行跳转（semantic-complete-jump-local）。

• C-c , J

Prompt for the name of a function defined in any file Emacs has parsed, and move point there (semantic-complete-jump).

提示 Emacs 已经分析过得任何文件中定义的函数名并跳转（semantic-complete-jump）。

• C-c , SPC

Display a list of possible completions for the symbol at point (semantic-complete-analyze-inline). This also activates a set of special key bindings for choosing a completion: RET accepts the current completion, M-n and M-p cycle through possible completions, TAB completes as far as possible and then cycles, and C-g or any other key aborts completion.

显示当前 point 处符号可能补全的列表（semantic-complete-analyze-inline）。这也会激活一组为了选择补全绑定的特殊键：RET 接受当前补全，M-n 和 M-p 轮换可用的不全选项，TAB 尽可能的补全然后循环，C-g 或其他任何键中断补全。

• C-c , l

Display a list of the possible completions of the symbol at point, in another window (semantic-analyze-possible-completions).

在另外的窗口中显示当前 point 处符号可能的补全列表。(semantic-analyze-possible-completions)

In addition to the above commands, the Semantic package provides a variety of other ways to make use of parser information. For instance, you can use it to display a list of completions when Emacs is idle. See Semantic in Semantic, for details.

### 1.11 26.11 Other Features Useful for Editing Programs

Some Emacs commands that aren’t designed specifically for editing programs are useful for that nonetheless.

The Emacs commands that operate on words, sentences and paragraphs are useful for editing code. Most symbols names contain words (see Words), while sentences can be found in strings and comments (see Sentences). As for paragraphs, they are defined in most programming language modes to begin and end at blank lines (see Paragraphs). Therefore, judicious use of blank lines to make the program clearer will also provide useful chunks of text for the paragraph commands to work on. Auto Fill mode, if enabled in a programming language major mode, indents the new lines which it creates.

Superword mode is a buffer-local minor mode that causes editing and motion commands to treat symbols (e.g., ‘this_is_a_symbol’) as words. When Superword mode is enabled, the minor mode indicator ‘²’ appears in the mode line. See also the similar subword-mode (see MixedCase Words).

Superword 模式是 buffer-local 辅助模式，可以是编辑和移动命令把符号（例如，‘this_is_a_symbol'）当做是单词操作。当启动 superword 模式时，模式行中显示辅助模式指示符‘²’。同样的还有 subword-mode（see MixCase words）。

Electric Layout mode (M-x electric-layout-mode) is a global minor mode that automatically inserts newlines when you type certain characters; for example, ‘{’, ‘}’ and ‘;’ in Javascript mode.

Electric Layout 模式（M-x electric-layout-mode）是一个全局辅助模式，当输入特定字符的时候会插入新行，比如，Javsscript 模式中的‘{’，‘}’和‘;’。

Apart from Hideshow mode (see Hideshow), another way to selectively display parts of a program is to use the selective display feature (see Selective Display). Programming modes often also support Outline minor mode (see Outline Mode), which can be used with the Foldout package (see Foldout).

Prettify Symbols mode is a buffer-local minor mode that replaces certain strings with more “attractive” versions for display purposes. For example, in Emacs Lisp mode, it replaces the string “lambda” with the Greek lambda character. You may wish to use this in non-programming modes as well. You can customize the mode by adding more entries to prettify-symbols-alist. There is also a global version, global-prettify-symbols-mode, which enables the mode in all buffers that support it.

Prettify Symbol 模式是一个 buffer-local 辅助模式，为了显示目的可以将指定字符串替换为更“有吸引力”的版本。例如，Emacs Lisp 模式中，它会将字符串“lambda”替换为希腊字母“λ”。可能希望在非编程模式中也使用它。可以通过向 prettify-symbos-alist 中添加更多条目来进行定制。还有一个全局版本，global-prettify-symbols-mode，可以在支持它的所有 buffer 中启用该模式。

Created: 2016-08-07 Sun 19:12

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