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XEmacs provides specialized support for editing source files for many different programming languages. For example it is possible to
The commands available for words, sentences, and paragraphs are useful in editing code even though their canonical application is for editing human language text. Most symbols contain words (see section Words); sentences can be found in strings and comments (see section Sentences). Paragraphs per se are not present in code, but the paragraph commands are useful anyway, because Lisp mode and C mode define paragraphs to begin and end at blank lines (see section Paragraphs). Judicious use of blank lines to make the program clearer also provides interesting chunks of text for the paragraph commands to work on.
The selective display feature is useful for looking at the overall structure of a function (see section Selective Display). This feature causes only the lines that are indented less than a specified amount to appear on the screen.
21.1 Major Modes for Programming Languages | Major modes for editing programs. | |
21.2 Lists and Sexps | Expressions with balanced parentheses. There are editing commands to operate on them. | |
21.3 Defuns | Each program is made up of separate functions. There are editing commands to operate on them. | |
21.4 Indentation for Programs | Adjusting indentation to show the nesting. | |
21.5 Automatic Display of Matching Parentheses | Insertion of a close-delimiter flashes matching open. | |
21.6 Manipulating Comments | Inserting, filling and aligning comments. | |
21.7 Editing Without Unbalanced Parentheses | Inserting two matching parentheses at once, etc. | |
21.8 Completion for Lisp Symbols | Completion on symbol names in Lisp code. | |
21.9 Documentation Commands | Getting documentation of functions you plan to call. | |
21.10 Change Logs | Maintaining a change history for your program. | |
21.11 Tags Tables | Go direct to any function in your program in one command. Tags remembers which file it is in. | |
21.12 Modes for C, C++, Java and similar languages | ||
21.13 Fortran Mode | Fortran mode and its special features. | |
21.14 Asm Mode | Asm mode and its special features. |
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Emacs has several major modes (see section Major Modes) to support programming languages. These major modes will typically understand language syntax, provide automatic indentation features, syntax based highlighting of text, and will often provide interfaces to the programming environment to assist in compiling, executing and debugging programs.
A language mode exist when someone decides to take the trouble to write it. At this time many widely used programming languages are supported by XEmacs. Examples include Ada, Awk, C, C++, CORBA (IDL), Fortran, Java, Lisp, Modula 2, Objective-C, Perl, Pike, Prolog, Python, Ruby, Scheme, Simula, SQL, Tcl, Unix Shell scripts, and VHDL. Some of these language have separate manuals, and some times more than one mode may be available for a language. For example, there are several variants of Lisp mode, which differ in the way they interface to Lisp execution. See section Major Modes for Lisp.
Major modes for programming language support are distributed in optional XEmacs packages (see section Packages) that must be installed before use. A notable exception to this rule is that a Lisp Mode is integral to XEmacs. The Programming Mode Package (‘prog-modes’) contains many such modes. Some languages are supported by packages of their own; prominent examples of such packages include ‘cc-mode’ for C, C++, Java, Objective C etc., ‘python-modes’ for Python, and ‘scheme’ for Scheme.
For a language named lang the major mode for the language will
typically be named lang-mode
. For example, the mode for C
is called c-mode
, that for Bourne shell scripts is called
sh-mode
and so on. These modes will invoke the functions listed
in the corresponding hook variables as a last step. See section Mode Hook Variables.
A mode can be invoked by typing M-x lang-mode <RET>. However this step is not normally required. If the package for a language mode is installed XEmacs usually knows when to automatically invoke the mode. This is normally done based on examining the file name to determine the language. Choosing Major Modes.
Each of the programming language modes defines the <TAB> key to run an indentation function that knows the indentation conventions of that language and updates the current line’s indentation accordingly. <LFD> is normally defined to do <RET> followed by <TAB>; thus it, too, indents in a mode-specific fashion.
In most programming languages, indentation is likely to vary from line to
line. So the major modes for those languages rebind <DEL> to treat a
tab as if it were the equivalent number of spaces (using the command
backward-delete-char-untabify
). This makes it possible to rub out
indentation one column at a time without worrying whether it is made up of
spaces or tabs. In these modes, use C-b C-d to delete a tab
character before point.
Programming language modes define paragraphs to be separated only by blank lines, so that the paragraph commands remain useful. Auto Fill mode, if enabled in a programming language major mode, indents the new lines which it creates.
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By convention, Emacs keys for dealing with balanced expressions are usually Control-Meta- characters. They tend to be analogous in function to their Control- and Meta- equivalents. These commands are usually thought of as pertaining to expressions in programming languages, but can be useful with any language in which some sort of parentheses exist (including English).
The commands fall into two classes. Some commands deal only with lists (parenthetical groupings). They see nothing except parentheses, brackets, braces (depending on what must balance in the language you are working with), and escape characters that might be used to quote those.
The other commands deal with expressions or sexps. The word ‘sexp’ is derived from s-expression, the term for a symbolic expression in Lisp. In Emacs, the notion of ‘sexp’ is not limited to Lisp. It refers to an expression in the language your program is written in. Each programming language has its own major mode, which customizes the syntax tables so that expressions in that language count as sexps.
Sexps typically include symbols, numbers, and string constants, as well as anything contained in parentheses, brackets, or braces.
In languages that use prefix and infix operators, such as C, it is not possible for all expressions to be sexps. For example, C mode does not recognize ‘foo + bar’ as an sexp, even though it is a C expression; it recognizes ‘foo’ as one sexp and ‘bar’ as another, with the ‘+’ as punctuation between them. This is a fundamental ambiguity: both ‘foo + bar’ and ‘foo’ are legitimate choices for the sexp to move over if point is at the ‘f’. Note that ‘(foo + bar)’ is a sexp in C mode.
Some languages have obscure forms of syntax for expressions that nobody has bothered to make Emacs understand properly.
Move forward over an sexp (forward-sexp
).
Move backward over an sexp (backward-sexp
).
Kill sexp forward (kill-sexp
).
Move up and backward in list structure (backward-up-list
).
Move down and forward in list structure (down-list
).
Move forward over a list (forward-list
).
Move backward over a list (backward-list
).
Transpose expressions (transpose-sexps
).
Put mark after following expression (mark-sexp
).
To move forward over an sexp, use C-M-f (forward-sexp
). If
the first significant character after point is an opening delimiter
(‘(’ in Lisp; ‘(’, ‘[’, or ‘{’ in C), C-M-f
moves past the matching closing delimiter. If the character begins a
symbol, string, or number, C-M-f moves over that. If the character
after point is a closing delimiter, C-M-f just moves past it. (This
last is not really moving across an sexp; it is an exception which is
included in the definition of C-M-f because it is as useful a
behavior as anyone can think of for that situation.)
The command C-M-b (backward-sexp
) moves backward over a
sexp. The detailed rules are like those above for C-M-f, but with
directions reversed. If there are any prefix characters (single quote,
back quote, and comma, in Lisp) preceding the sexp, C-M-b 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, it moves in the opposite direction.
Killing an sexp at a time can be done with C-M-k (kill-sexp
).
C-M-k kills the characters that C-M-f would move over.
The list commands, C-M-n (forward-list
) and
C-M-p (backward-list
), move over lists like the sexp
commands but skip over any number of other kinds of sexps (symbols,
strings, etc). In some situations, these commands are useful because
they usually ignore comments, since the comments usually do not contain
any lists.
C-M-n and C-M-p stay at the same level in parentheses, when
that is possible. 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
direction of motion and also requests repetition, so it moves forward and
up one or more levels.
To move down in list 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 of parentheses to go down.
C-M-t (transpose-sexps
) drags the previous sexp across
the next one. An argument serves as a repeat count, and a negative
argument drags backwards (thus canceling out the effect of C-M-t with
a positive argument). An argument of zero, rather than doing nothing,
transposes the sexps ending after point and the mark.
To make the region be the next sexp in the buffer, use C-M-@
(mark-sexp
) which sets the mark at the same place that
C-M-f would move to. C-M-@ takes arguments like
C-M-f. In particular, a negative argument is useful for putting
the mark at the beginning of the previous sexp.
The list and sexp commands’ understanding of syntax is completely controlled by the syntax table. Any character can, for example, be declared to be an opening delimiter and act like an open parenthesis. See section The Syntax Table.
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In Emacs, a parenthetical grouping at the top level in the buffer is
called a defun. The name derives from the fact that most
top-level lists in Lisp are instances of the special operator
defun
, but Emacs calls any top-level parenthetical
grouping counts a defun regardless of its contents or
the programming language. For example, in C, the body of a
function definition is a defun.
Move to beginning of current or preceding defun
(beginning-of-defun
).
Move to end of current or following defun (end-of-defun
).
Put region around whole current or following defun (mark-defun
).
The commands to move to the beginning and end of the current defun are
C-M-a (beginning-of-defun
) and C-M-e (end-of-defun
).
To operate on the current defun, use C-M-h (mark-defun
)
which puts point at the beginning and the mark at the end of the current
or next defun. This is the easiest way to prepare for moving the defun
to a different place. In C mode, C-M-h runs the function
mark-c-function
, which is almost the same as mark-defun
,
but which backs up over the argument declarations, function name, and
returned data type so that the entire C function is inside the region.
To compile and evaluate the current defun, use M-x compile-defun. This function prints the results in the minibuffer. If you include an argument, it inserts the value in the current buffer after the defun.
Emacs assumes that any open-parenthesis found in the leftmost column is the start of a defun. Therefore, never put an open-parenthesis at the left margin in a Lisp file unless it is the start of a top level list. Never put an open-brace or other opening delimiter at the beginning of a line of C code unless it starts the body of a function. The most likely problem case is when you want an opening delimiter at the start of a line inside a string. To avoid trouble, put an escape character (‘\’ in C and Emacs Lisp, ‘/’ in some other Lisp dialects) before the opening delimiter. It will not affect the contents of the string.
The original Emacs found defuns by moving upward a level of parentheses until there were no more levels to go up. This required scanning back to the beginning of the buffer for every function. To speed this up, Emacs was changed to assume that any ‘(’ (or other character assigned the syntactic class of opening-delimiter) at the left margin is the start of a defun. This heuristic is nearly always right; however, it mandates the convention described above.
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The best way to keep a program properly indented (“ground”) is to use Emacs to re-indent it as you change the program. Emacs has commands to indent properly either a single line, a specified number of lines, or all of the lines inside a single parenthetical grouping.
21.4.1 Basic Program Indentation Commands | ||
21.4.2 Indenting Several Lines | Commands to reindent many lines at once. | |
21.4.3 Customizing Lisp Indentation | Specifying how each Lisp function should be indented. |
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Adjust indentation of current line.
Equivalent to <RET> followed by <TAB> (newline-and-indent
).
The basic indentation command is <TAB>, which gives the current
line the correct indentation as determined from the previous lines. The
function that <TAB> runs depends on the major mode; it is
lisp-indent-line
in Lisp mode, c-indent-line
in C mode,
etc. These functions understand different syntaxes for different
languages, but they all do about the same thing. <TAB> in any
programming language major mode inserts or deletes whitespace at the
beginning of the current line, independent of where point is in the
line. If point is inside the whitespace at the beginning of the line,
<TAB> leaves it at the end of that whitespace; otherwise, <TAB>
leaves point fixed with respect to the characters around it.
Use C-q <TAB> to insert a tab at point.
When entering a large amount of new code, use <LFD>
(newline-and-indent
), which is equivalent to a <RET> followed
by a <TAB>. <LFD> creates a blank line, then gives it the
appropriate indentation.
<TAB> indents the second and following lines of the body of a parenthetical grouping each under the preceding one; therefore, if you alter one line’s indentation to be nonstandard, the lines below tend to follow it. This is the right behavior in cases where the standard result of <TAB> does not look good.
Remember that Emacs assumes that an open-parenthesis, open-brace, or other opening delimiter at the left margin (including the indentation routines) is the start of a function. You should therefore never have an opening delimiter in column zero that is not the beginning of a function, not even inside a string. This restriction is vital for making the indentation commands fast. See section Defuns, for more information on this behavior.
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Several commands are available to re-indent several lines of code which have been altered or moved to a different level in a list structure.
Re-indent all the lines within one list (indent-sexp
).
Shift an entire list rigidly sideways so that its first line is properly indented.
Re-indent all lines in the region (indent-region
).
To re-indent the contents of a single list, position point before the
beginning of it and type C-M-q. This key is bound to
indent-sexp
in Lisp mode, indent-c-exp
in C mode, and
bound to other suitable functions in other modes. The indentation of
the line the sexp starts on is not changed; therefore, only the relative
indentation within the list, and not its position, is changed. To
correct the position as well, type a <TAB> before C-M-q.
If the relative indentation within a list is correct but the indentation of its beginning is not, go to the line on which the list begins and type C-u <TAB>. When you give <TAB> a numeric argument, it moves all the lines in the group, starting on the current line, sideways the same amount that the current line moves. The command does not move lines that start inside strings, or C preprocessor lines when in C mode.
Another way to specify a range to be re-indented is with point and
mark. The command C-M-\ (indent-region
) applies <TAB>
to every line whose first character is between point and mark.
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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.
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
always indent the second line by
lisp-body-indention
extra columns beyond the open-parenthesis
starting the expression.
Individual functions can override the standard pattern in various
ways, according to the lisp-indent-function
property of the
function name. (Note: lisp-indent-function
was formerly called
lisp-indent-hook
). There are four possibilities for this
property:
nil
This is the same as no property; the standard indentation pattern is used.
defun
The pattern used for function names that start with def
is used for
this function also.
The first number arguments of the function are
distinguished arguments; the rest are considered the body
of the expression. A line in the expression is indented according to
whether the first argument on it is distinguished or not. If the
argument is part of the body, the line is indented lisp-body-indent
more columns than the open-parenthesis starting the containing
expression. If the argument is distinguished and is either the first
or second argument, it is indented twice that many extra columns.
If the argument is distinguished and not the first or second argument,
the standard pattern is followed for that line.
symbol should be a function name; that function is called to calculate the indentation of a line within this expression. The function receives two arguments:
The value returned by parse-partial-sexp
(a Lisp primitive for
indentation and nesting computation) when it parses up to the
beginning of this line.
The position at which the line being indented begins.
It should return either a number, which is the number of columns of indentation for that line, or a list whose first element is such a number. The difference between returning a number and returning a list is that a number says that all following lines at the same nesting level should be indented just like this one; a list says that following lines might call for different indentations. This makes a difference when the indentation is computed by C-M-q; if the value is a number, C-M-q need not recalculate indentation for the following lines until the end of the list.
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The Emacs parenthesis-matching feature shows you automatically how parentheses match in the text. Whenever a self-inserting character that is a closing delimiter is typed, the cursor moves momentarily to the location of the matching opening delimiter, provided that is visible on the screen. If it is not on the screen, some text starting with that opening delimiter is displayed in the echo area. Either way, you see the grouping you are closing off.
In Lisp, automatic matching applies only to parentheses. In C, it also applies to braces and brackets. Emacs knows which characters to regard as matching delimiters based on the syntax table set by the major mode. See section The Syntax Table.
If the opening delimiter and closing delimiter are mismatched—as in ‘[x)’—the echo area displays a warning message. The correct matches are specified in the syntax table.
Two variables control parenthesis matching displays.
blink-matching-paren
turns the feature on or off. The default is
t
(match display is on); nil
turns it off.
blink-matching-paren-distance
specifies how many characters back
Emacs searches to find a matching opening delimiter. If the match is
not found in the specified region, scanning stops, and nothing is
displayed. This prevents wasting lots of time scanning when there is no
match. The default is 4000.
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The comment commands insert, kill and align comments.
Insert or align comment (indent-for-comment
).
Set comment column (set-comment-column
).
Kill comment on current line (kill-comment
).
Like <RET> followed by inserting and aligning a comment
(indent-new-comment-line
).
The command that creates a comment is Meta-;
(indent-for-comment
). If there is no comment already on the
line, a new comment is created and aligned at a specific column called
the comment column. Emacs creates the comment by inserting the
string at the value of comment-start
; see below. Point is left
after that string. If the text of the line extends past the comment
column, indentation is done to a suitable boundary (usually, at least
one space is inserted). If the major mode has specified a string to
terminate comments, that string is inserted after point, to keep the
syntax valid.
You can also use Meta-; to align an existing comment. If a line already contains the string that starts comments, M-; just moves point after it and re-indents it to the conventional place. Exception: comments starting in column 0 are not moved.
Some major modes have special rules for indenting certain kinds of comments in certain contexts. For example, in Lisp code, comments which start with two semicolons are indented as if they were lines of code, instead of at the comment column. Comments which start with three semicolons are supposed to start at the left margin. Emacs understands these conventions by indenting a double-semicolon comment using <TAB> and by not changing the indentation of a triple-semicolon comment at all.
;; 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. |
In C code, a comment preceded on its line by nothing but whitespace is indented like a line of code.
Even when an existing comment is properly aligned, M-; is still useful for moving directly to the start of the comment.
C-u - C-x ; (kill-comment
) kills the comment on the
current line, if there is one. The indentation before the start of the
comment is killed as well. If there does not appear to be a comment in
the line, nothing happens. To reinsert the comment on another line,
move to the end of that line, type first C-y, and then M-;
to realign the comment. Note that C-u - C-x ; is not a distinct
key; it is C-x ; (set-comment-column
) with a negative
argument. That command is programmed to call kill-comment
when
called with a negative argument. However, kill-comment
is a
valid command which you could bind directly to a key if you wanted to.
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If you are typing a comment and want to continue it on another line,
use the command Meta-<LFD> (indent-new-comment-line
),
which terminates the comment you are typing, creates a new blank line
afterward, and begins a new comment indented under the old one. If
Auto Fill mode is on and you go past the fill column while typing, the
comment is continued in just this fashion. If point is
not at the end of the line when you type M-<LFD>, the text on
the rest of the line becomes part of the new comment line.
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The comment column is stored in the variable comment-column
. You
can explicitly set it to a number. Alternatively, the command C-x ;
(set-comment-column
) sets the comment column to the column point is
at. C-u C-x ; sets the comment column to match the last comment
before point in the buffer, and then calls Meta-; to align the
current line’s comment under the previous one. Note that C-u - C-x ;
runs the function kill-comment
as described above.
comment-column
is a per-buffer variable; altering the variable
affects only the current buffer. You can also change the default value.
See section Local Variables. Many major modes initialize this variable
for the current buffer.
The comment commands recognize comments based on the regular expression
that is the value of the variable comment-start-skip
. This regexp
should 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 "/\\*+ *"
, which matches extra
stars and spaces after the ‘/*’ itself. (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 section Syntax of Regular Expressions.)
When a comment command makes a new comment, it inserts the value of
comment-start
to begin it. The value of comment-end
is
inserted after point and will follow the text you will insert
into the comment. In C mode, comment-start
has the value
"/* "
and comment-end
has the value " */"
.
comment-multi-line
controls how M-<LFD>
(indent-new-comment-line
) behaves when used inside a comment. If
comment-multi-line
is nil
, as it normally is, then
M-<LFD> terminates the comment on the starting line and starts
a new comment on the new following line. If comment-multi-line
is not nil
, then M-<LFD> sets up the new following line
as part of the same comment that was found on the starting line. This
is done by not inserting a terminator on the old line and not inserting
a starter on the new line. In languages where multi-line comments are legal,
the value you choose for this variable is a matter of taste.
The variable comment-indent-hook
should contain a function that
is called to compute the indentation for a newly inserted comment or for
aligning an existing comment. Major modes set this variable differently.
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. The function should return the column in which the comment
ought to start. For example, in Lisp mode, the indent hook function
bases its decision on the number of semicolons that begin an existing
comment and on the code in the preceding lines.
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Put parentheses around next sexp(s) (insert-parentheses
).
Move past next close parenthesis and re-indent
(move-over-close-and-reindent
).
The commands M-( (insert-parentheses
) and M-)
(move-over-close-and-reindent
) are designed to facilitate a style of
editing which keeps parentheses balanced at all times. M-( inserts a
pair of parentheses, either together as in ‘()’, or, if given an
argument, around the next several sexps, and leaves point after the open
parenthesis. Instead of typing ( F O O ), you can type M-( F O
O, which has the same effect except for leaving the cursor before the
close parenthesis. You can then type M-), which moves past the
close parenthesis, deletes any indentation preceding it (in this example
there is none), and indents with <LFD> after it.
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Completion usually happens in the minibuffer. An exception is completion for Lisp symbol names, which is available in all buffers.
The command M-<TAB> (lisp-complete-symbol
) takes the
partial Lisp symbol before point to be an abbreviation, and compares it
against all non-trivial Lisp symbols currently known to Emacs. Any
additional characters that they all have in common are inserted at point.
Non-trivial symbols are those that have function definitions, values, or
properties.
If there is an open-parenthesis immediately before the beginning of the partial symbol, only symbols with function definitions are considered as completions.
If the partial name in the buffer has more than one possible completion and they have no additional characters in common, a list of all possible completions is displayed in another window.
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As you edit Lisp code to be run in Emacs, you can use the commands
C-h f (describe-function
) and C-h v
(describe-variable
) to print documentation of functions and
variables you want to call. These commands use the minibuffer to
read the name of a function or variable to document, and display the
documentation in a window.
For extra convenience, these commands provide default arguments based on the code in the neighborhood of point. C-h f sets the default to the function called in the innermost list containing point. C-h v uses the symbol name around or adjacent to point as its default.
The M-x manual-entry command gives you access to documentation
on Unix commands, system calls, and libraries. The command reads a
topic as an argument, and displays the Unix manual page for that topic.
manual-entry
always searches all 8 sections of the
manual and concatenates all the entries it finds. For example,
the topic ‘termcap’ finds the description of the termcap library
from section 3, followed by the description of the termcap data base
from section 5.
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The Emacs command M-x add-change-log-entry helps you keep a record of when and why you have changed a program. It assumes that you have a file in which you write a chronological sequence of entries describing individual changes. The default is to store the change entries in a file called ‘ChangeLog’ in the same directory as the file you are editing. The same ‘ChangeLog’ file therefore records changes for all the files in a directory.
A change log entry starts with a header line that contains your name and the current date. Except for these header lines, every line in the change log starts with a tab. One entry can describe several changes; each change starts with a line starting with a tab and a star. M-x add-change-log-entry visits the change log file and creates a new entry unless the most recent entry is for today’s date and your name. In either case, it adds a new line to start the description of another change just after the header line of the entry. When M-x add-change-log-entry is finished, all is prepared for you to edit in the description of what you changed and how. You must then save the change log file yourself.
The change log file is always visited in Indented Text mode, which means that <LFD> and auto-filling indent each new line like the previous line. This is convenient for entering the contents of an entry, which must be indented. See section Text Mode.
Here is an example of the formatting conventions used in the change log for Emacs:
Wed Jun 26 19:29:32 1985 Richard M. Stallman (rms at mit-prep) * xdisp.c (try_window_id): If C-k is done at end of next-to-last line, this fn updates window_end_vpos and cannot leave window_end_pos nonnegative (it is zero, in fact). If display is preempted before lines are output, this is inconsistent. Fix by setting blank_end_of_window to nonzero. Tue Jun 25 05:25:33 1985 Richard M. Stallman (rms at mit-prep) * cmds.c (Fnewline): Call the auto fill hook if appropriate. * xdisp.c (try_window_id): If point is found by compute_motion after xp, record that permanently. If display_text_line sets point position wrong (case where line is killed, point is at eob and that line is not displayed), set it again in final compute_motion. |
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A tags table is a description of how a multi-file program is broken up into files. It lists the names of the component files and the names and positions of the functions (or other named subunits) in each file. Grouping the related files makes it possible to search or replace through all the files with one command. Recording the function names and positions makes possible the M-. command which finds the definition of a function by looking up which of the files it is in.
Tags tables are stored in files called tags table files. The conventional name for a tags table file is ‘TAGS’.
Each entry in the tags table records the name of one tag, the name of the file that the tag is defined in (implicitly), and the position in that file of the tag’s definition.
Just what names from the described files are recorded in the tags table depends on the programming language of the described file. They normally include all functions and subroutines, and may also include global variables, data types, and anything else convenient. Each name recorded is called a tag.
The Ebrowse is a separate facility tailored for C++, with tags and a class browser. See (ebrowse)Ebrowse section ‘Ebrowse’ in Ebrowse User’s Manual.
21.11.1 Source File Tag Syntax | Tag syntax for various types of code and text files. | |
21.11.2 Creating Tags Tables | Creating a tags table with etags .
| |
21.11.3 Etags Regexps | Create arbitrary tags using regular expressions. | |
21.11.4 Selecting a Tags Table | How to visit a tags table. | |
21.11.5 Finding a Tag | Commands to find the definition of a specific tag. | |
21.11.6 Searching and Replacing with Tags Tables | Using a tags table for searching and replacing. | |
21.11.7 Tags Table Inquiries | Listing and finding tags defined in a file. |
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Here is how tag syntax is defined for the most popular languages:
struct
, union
and enum
. You can tag function
declarations and external variables in addition to function definitions
by giving the ‘--declarations’ option to etags
.
#define
macro definitions and enum
constants are also
tags, unless you specify ‘--no-defines’ when making the tags table.
Similarly, global variables are tags, unless you specify
‘--no-globals’. Use of ‘--no-globals’ and ‘--no-defines’
can make the tags table file much smaller.
operator
functions tags are
named, for example ‘operator+’.
interface
, extends
and implements
constructs.
Tags for variables and functions in classes are named
‘class.variable’ and ‘class.function’.
\chapter
,
\section
, \subsection
, \subsubsection
,
\eqno
, \label
, \ref
, \cite
, \bibitem
,
\part
, \appendix
, \entry
, or \index
, is a
tag.
Other commands can make tags as well, if you specify them in the
environment variable TEXTAGS
before invoking etags
. The
value of this environment variable should be a colon-separated list of
command names. For example,
TEXTAGS="def:newcommand:newenvironment" export TEXTAGS |
specifies (using Bourne shell syntax) that the commands ‘\def’, ‘\newcommand’ and ‘\newenvironment’ also define tags.
defun
, any variable
defined with defvar
or defconst
, and in general the first
argument of any expression that starts with ‘(def’ in column zero, is
a tag.
def
or with a
construct whose name starts with ‘def’. They also include variables
set with set!
at top level in the file.
Several other languages are also supported:
With Ada, it is possible to have the same name used for different entity kinds (e.g. the same name for a procedure and a function). Also, for things like packages, procedures and functions, there is the spec (i.e. the interface) and the body (i.e. the implementation). To facilitate the choice to the user, a tag value is appended with a qualifier:
/f
/p
/s
/b
/t
/k
So, as an example, M-x find-tag bidule/b will go directly to the body of the package bidule while M-x find-tag bidule will just search for any tag bidule.
sub
,
my
and local
keywords. Use ‘--globals’ if you want
to tag global variables.
def
or class
at the beginning of a line
generate a tag.
You can also generate tags based on regexp matching (see section Etags Regexps) to handle other formats and languages.
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The etags
program is used to create a tags table file. It knows
the syntax of several languages, as described in
Here is how to run etags
:
etags inputfiles… |
The etags
program reads the specified files, and writes a tags
table named ‘TAGS’ in the current working directory. You can
intermix compressed and plain text source file names. etags
knows about the most common compression formats, and does the right
thing. So you can compress all your source files and have etags
look for compressed versions of its file name arguments, if it does not
find uncompressed versions. Under MS-DOS, etags
also looks for
file names like ‘mycode.cgz’ if it is given ‘mycode.c’ on the
command line and ‘mycode.c’ does not exist.
etags
recognizes the language used in an input file based on
its file name and contents. You can specify the language with the
‘--language=name’ option, described below.
If the tags table data become outdated due to changes in the files described in the table, the way to update the tags table is the same way it was made in the first place. It is not necessary to do this often.
If the tags table fails to record a tag, or records it for the wrong file, then Emacs cannot possibly find its definition. However, if the position recorded in the tags table becomes a little bit wrong (due to some editing in the file that the tag definition is in), the only consequence is a slight delay in finding the tag. Even if the stored position is very wrong, Emacs will still find the tag, but it must search the entire file for it.
So you should update a tags table when you define new tags that you want to have listed, or when you move tag definitions from one file to another, or when changes become substantial. Normally there is no need to update the tags table after each edit, or even every day.
One tags table can effectively include another. Specify the included tags file name with the ‘--include=file’ option when creating the file that is to include it. The latter file then acts as if it contained all the files specified in the included file, as well as the files it directly contains.
If you specify the source files with relative file names when you run
etags
, the tags file will contain file names relative to the
directory where the tags file was initially written. This way, you can
move an entire directory tree containing both the tags file and the
source files, and the tags file will still refer correctly to the source
files.
If you specify absolute file names as arguments to etags
, then
the tags file will contain absolute file names. This way, the tags file
will still refer to the same files even if you move it, as long as the
source files remain in the same place. Absolute file names start with
‘/’, or with ‘device:/’ on MS-DOS and MS-Windows.
When you want to make a tags table from a great number of files, you
may have problems listing them on the command line, because some systems
have a limit on its length. The simplest way to circumvent this limit
is to tell etags
to read the file names from its standard input,
by typing a dash in place of the file names, like this:
find . -name "*.[chCH]" -print | etags - |
Use the option ‘--language=name’ to specify the language
explicitly. You can intermix these options with file names; each one
applies to the file names that follow it. Specify
‘--language=auto’ to tell etags
to resume guessing the
language from the file names and file contents. Specify
‘--language=none’ to turn off language-specific processing
entirely; then etags
recognizes tags by regexp matching alone
(see section Etags Regexps).
‘etags --help’ prints the list of the languages etags
knows, and the file name rules for guessing the language. It also prints
a list of all the available etags
options, together with a short
explanation.
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The ‘--regex’ option provides a general way of recognizing tags based on regexp matching. You can freely intermix it with file names. Each ‘--regex’ option adds to the preceding ones, and applies only to the following files. The syntax is:
--regex=/tagregexp[/nameregexp]/ |
where tagregexp is used to match the lines to tag. It is always
anchored, that is, it behaves as if preceded by ‘^’. If you want
to account for indentation, just match any initial number of blanks by
beginning your regular expression with ‘[ \t]*’. In the regular
expressions, ‘\’ quotes the next character, and ‘\t’ stands
for the tab character. Note that etags
does not handle the other
C escape sequences for special characters.
The syntax of regular expressions in etags
is the same as in
Emacs, augmented with the interval operator, which works as in
grep
and ed
. The syntax of an interval operator is
‘\{m,n\}’, and its meaning is to match the preceding
expression at least m times and up to n times.
You should not match more characters with tagregexp than that needed to recognize what you want to tag. If the match is such that more characters than needed are unavoidably matched by tagregexp (as will usually be the case), you should add a nameregexp, to pick out just the tag. This will enable Emacs to find tags more accurately and to do completion on tag names more reliably. You can find some examples below.
The option ‘--ignore-case-regex’ (or ‘-c’) is like ‘--regex’, except that the regular expression provided will be matched without regard to case, which is appropriate for various programming languages.
The ‘-R’ option deletes all the regexps defined with ‘--regex’ options. It applies to the file names following it, as you can see from the following example:
etags --regex=/reg1/ voo.doo --regex=/reg2/ \ bar.ber -R --lang=lisp los.er |
Here etags
chooses the parsing language for ‘voo.doo’ and
‘bar.ber’ according to their contents. etags
also uses
reg1 to recognize additional tags in ‘voo.doo’, and both
reg1 and reg2 to recognize additional tags in
‘bar.ber’. etags
uses the Lisp tags rules, and no regexp
matching, to recognize tags in ‘los.er’.
A regular expression can be bound to a given language, by prepending
it with ‘{lang}’. When you do this, etags
will use the
regular expression only for files of that language. ‘etags --help’
prints the list of languages recognised by etags
. The following
example tags the DEFVAR
macros in the Emacs source files.
etags
applies this regular expression to C files only:
--regex='{c}/[ \t]*DEFVAR_[A-Z_ \t(]+"\([^"]+\)"/' |
This feature is particularly useful when storing a list of regular
expressions in a file. The following option syntax instructs
etags
to read two files of regular expressions. The regular
expressions contained in the second file are matched without regard to
case.
--regex=@first-file --ignore-case-regex=@second-file |
A regex file contains one regular expressions per line. Empty lines,
and lines beginning with space or tab are ignored. When the first
character in a line is ‘@’, etags
assumes that the rest of
the line is the name of a file of regular expressions. This means that
such files can be nested. All the other lines are taken to be regular
expressions. For example, one can create a file called
‘emacs.tags’ with the following contents (the first line in the
file is a comment):
-- This is for GNU Emacs source files {c}/[ \t]*DEFVAR_[A-Z_ \t(]+"\([^"]+\)"/\1/ |
and then use it like this:
etags --regex=@emacs.tags *.[ch] */*.[ch] |
Here are some more examples. The regexps are quoted to protect them from shell interpretation.
etags --language=none \ --regex='/[ \t]*function.*=[ \t]*\([^ \t]*\)[ \t]*(/\1/' \ --regex='/###key \(.*\)/\1/' \ --regex='/[ \t]*global[ \t].*/' \ *.m |
Note that tags are not generated for scripts so that you have to add a line by yourself of the form ‘###key <script-name>’ if you want to jump to it.
etags --language=none --regex='/proc[ \t]+\([^ \t]+\)/\1/' *.tcl |
--language=none \ --regex='/[ \t]*\(ARCHITECTURE\|CONFIGURATION\) +[^ ]* +OF/' \ --regex='/[ \t]*\(ATTRIBUTE\|ENTITY\|FUNCTION\|PACKAGE\ \( BODY\)?\|PROCEDURE\|PROCESS\|TYPE\)[ \t]+\([^ \t(]+\)/\3/' |
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At any time Emacs has one selected tags table, and all the commands
for working with tags tables use the selected one. To select a tags table,
use the variable tag-table-alist
.
The value of tag-table-alist
is a list that determines which
TAGS
files should be active for a given buffer. This is not
really an association list, in that all elements are checked. The car
of each element of this list is a pattern against which the buffers file
name is compared; if it matches, then the cdr of the list should be the
name of the tags table to use. If more than one element of this list
matches the buffers file name, all of the associated tags tables are
used. Earlier ones are searched first.
If the car of elements of this list are strings, they are treated
as regular-expressions against which the file is compared (like the
auto-mode-alist
). If they are not strings, they are evaluated.
If they evaluate to non-nil
, the current buffer is considered to
match.
If the cdr of the elements of this list are strings, they are assumed to name a tags file. If they name a directory, the string ‘tags’ is appended to them to get the file name. If they are not strings, they are evaluated and must return an appropriate string.
For example:
(setq tag-table-alist '(("/usr/src/public/perl/" . "/usr/src/public/perl/perl-3.0/") ("\\.el$" . "/usr/local/emacs/src/") ("/jbw/gnu/" . "/usr15/degree/stud/jbw/gnu/") ("" . "/usr/local/emacs/src/") )) |
The example defines the tags table alist in the following way:
If you had a file called ‘/usr/jbw/foo.el’, it would use both
‘TAGS’ files,
‘/usr/local/emacs/src/TAGS’ and
‘/usr15/degree/stud/jbw/gnu/TAGS’ (in that order), because it
matches both patterns.
If the buffer-local variable buffer-tag-table
is set, it names a
tags table that is searched before all others when find-tag
is
executed from this buffer.
If there is a file called ‘TAGS’ in the same directory as the file
in question, then that tags file will always be used as well (after the
buffer-tag-table
but before the tables specified by this list).
If the variable tags-file-name
is set, the ‘TAGS’ file it names
will apply to all buffers (for backwards compatibility.) It is searched
first.
If the value of the variable tags-always-build-completion-table
is t
, the tags file will always be added to the completion table
without asking first, regardless of the size of the tags file.
The function M-x visit-tags-table, is largely made obsolete by
the variable tag-table-alist
, tells tags commands to use the tags
table file file first. The file should be the name of a
file created with the etags
program. A directory name is also
acceptable; it means the file ‘TAGS’ in that directory. The
function only stores the file name you provide in the variable
tags-file-name
. Emacs does not actually read in the tags table
contents until you try to use them. You can set the variable explicitly
instead of using visit-tags-table
. The value of the variable
tags-file-name
is the name of the tags table used by all buffers.
This is for backward compatibility, and is largely supplanted by the
variable tag-table-alist
.
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The most important thing that a tags table enables you to do is to find the definition of a specific tag.
Find first definition of tag (find-tag
).
Find next alternate definition of last tag specified.
Find first definition of tag, but display it in another window
(find-tag-other-window
).
M-. (find-tag
) is the command to find the definition of
a specified tag. It searches through the tags table for that tag, as a
string, then uses the tags table information to determine the file in
which the definition is used and the approximate character position of
the definition in the file. Then find-tag
visits the file,
moves point to the approximate character position, and starts searching
ever-increasing distances away for the text that should appear at
the beginning of the definition.
If an empty argument is given (by typing <RET>), the sexp in the buffer before or around point is used as the name of the tag to find. See section Lists and Sexps, for information on sexps.
The argument to find-tag
need not be the whole tag name; it can
be a substring of a tag name. However, there can be many tag names
containing the substring you specify. Since find-tag
works by
searching the text of the tags table, it finds the first tag in the table
that the specified substring appears in. To find other tags that match
the substring, give find-tag
a numeric argument, as in C-u
M-.. This does not read a tag name, but continues searching the tag
table’s text for another tag containing the same substring last used.
If your keyboard has a real <META> key, M-0 M-. is an easier
alternative to C-u M-..
If the optional second argument other-window is non-nil
, it uses
another window to display the tag.
Multiple active tags tables and completion are supported.
Variables of note include the following:
Controls which tables apply to which buffers.
Stores a default tags table.
Controls completion behavior.
Specifies a buffer-local table.
Sets whether tags tables should be very hidden.
Specifies how many tags-based hops to remember.
Like most commands that can switch buffers, find-tag
has another
similar command that displays the new buffer in another window. C-x 4
. invokes the function find-tag-other-window
. (This key sequence
ends with a period.)
Emacs comes with a tags table file ‘TAGS’ (in the directory
containing Lisp libraries) that includes all the Lisp libraries and all
the C sources of Emacs. By specifying this file with visit-tags-table
and then using M-. you can quickly look at the source of any Emacs
function.
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The commands in this section visit and search all the files listed in the selected tags table, one by one. For these commands, the tags table serves only to specify a sequence of files to search. A related command is M-x grep (see section Running “make”, or Compilers Generally).
Search for regexp through the files in the selected tags table.
Perform a query-replace-regexp
on each file in the selected tags table.
Restart one of the commands above, from the current location of point
(tags-loop-continue
).
M-x tags-search reads a regexp using the minibuffer, then
searches for matches in all the files in the selected tags table, one
file at a time. It displays the name of the file being searched so you
can follow its progress. As soon as it finds an occurrence,
tags-search
returns.
Having found one match, you probably want to find all the rest. To find
one more match, type M-, (tags-loop-continue
) to resume the
tags-search
. This searches the rest of the current buffer, followed
by the remaining files of the tags table.
M-x tags-query-replace performs a single
query-replace-regexp
through all the files in the tags table. It
reads a regexp to search for and a string to replace with, just like
ordinary M-x query-replace-regexp. It searches much like M-x
tags-search, but repeatedly, processing matches according to your
input. See section Replacement Commands, for more information on query replace.
It is possible to get through all the files in the tags table with a single invocation of M-x tags-query-replace. But often it is useful to exit temporarily, which you can do with any input event that has no special query replace meaning. You can resume the query replace subsequently by typing M-,; this command resumes the last tags search or replace command that you did.
The commands in this section carry out much broader searches than the
find-tag
family. The find-tag
commands search only for
definitions of tags that match your substring or regexp. The commands
tags-search
and tags-query-replace
find every occurrence
of the regexp, as ordinary search commands and replace commands do in
the current buffer.
These commands create buffers only temporarily for the files that they have to search (those which are not already visited in Emacs buffers). Buffers in which no match is found are quickly killed; the others continue to exist.
It may have struck you that tags-search
is a lot like
grep
. You can also run grep
itself as an inferior of
Emacs and have Emacs show you the matching lines one by one. This works
much like running a compilation; finding the source locations of the
grep
matches works like finding the compilation errors.
See section Running “make”, or Compilers Generally.
If you wish to process all the files in a selected tags table, but M-x tags-search and M-x tags-query-replace are not giving you the desired result, you can use M-x next-file.
With a numeric argument, regardless of its value, visit the first file in the tags table and prepare to advance sequentially by files.
Visit the next file in the selected tags table.
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Display a list of the tags defined in a specific program file.
Display a list of all tags matching a specified regexp.
M-x list-tags reads the name of one of the files described by the selected tags table, and displays a list of all the tags defined in that file. The “file name” argument is really just a string to compare against the names recorded in the tags table; it is read as a string rather than a file name. Therefore, completion and defaulting are not available, and you must enter the string the same way it appears in the tag table. Do not include a directory as part of the file name unless the file name recorded in the tags table contains that directory.
M-x tags-apropos is like apropos
for tags. It reads a regexp,
then finds all the tags in the selected tags table whose entries match that
regexp, and displays the tag names found.
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The recommended means for supporting the “C–like” programming languages in XEmacs is the ‘cc-mode’ package. CC Mode is not included in the basic XEmacs distribution but is available as an optional package. If loading a file whose names ends in the ‘.cc’ extension does not automatically invoke a C++ Mode then the ‘cc-mode’ package is probably not yet installed. See section Packages.
CC Mode provides modes for editing source files in Awk
(awk-mode
), C (c-mode
), C++ (c++-mode
), CORBA IDL
(idl-mode
), Java (java-mode
), Objective C
(objc-mode
), and Pike (pike-mode
). All these languages are
supported with an sophisticated “indentation engine” that is feature
rich, customizable and quite efficient.
Each language major mode runs hooks in the conventionally named hook
variables (see section Mode Hook Variables). In addition to this conventional
behavior all the CC Mode major modes will also run hooks in
c-mode-common-hook
before invoking the major mode specific
hook.
CC Mode runs any hooks in c-initialization-hook
exactly once
when it is first loaded.
CC Mode is a very comprehensive and flexible system and full description of its capabilities is beyond the scope of this manual. It is strongly recommended that the reader consult the CC Mode documentation for details once the package has been installed. See CC Mode: (cc-mode)Top section ‘Top’ in The CC Mode Manual.
21.12.1 Older Modes for C and AWK | ||
21.12.2 Customizing Indentation in CC Mode | An Introduction to Customizing CC Mode. |
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XEmacs provides older versions of a C Mode and an AWK Mode in the ‘prog-modes’ package. These older modes do not share the indentation engine in CC Mode have have their own specific means of customizing indentation. To use these modes the ‘prog-modes’ package must be installed.
This older C mode is known simply as the “Old C Mode”. It supports only the C language and it lacks many of the features of CC Mode. However the old C mode offers modest space requirements and very fast operation. Old C Mode might be useful in space constrained environments, on slow machines, or for editing very large files. This old C mode is available in the ‘old-c-mode’ library. See Old C Mode: (prog-modes)old-c-mode section ‘old-c-mode’ in The Programming Modes Package Manual.
The old AWK mode exists for similar reasons. It is available in the ‘awk-mode’ library. See Old AWK Mode: (prog-modes)awk-mode section ‘awk-mode’ in The Programming Modes Package Manual.
Note that the prog-modes package will never automatically invoke these older modes for a user. However installing the ‘cc-mode’ package will make CC Mode’s versions available automatically. As a result a user who wants to use these older modes must explicitly load the old libraries to use them.
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A very brief introduction is included here on customizing CC Mode. CC Mode has many features, including useful minor modes, that are completely documented in its own manual.
CC Mode implements several different “styles” for C code (and the
other languages supported by CC Mode). If you need to change the
indentation style for CC Mode it is recommended that you first see if an
existing style meets your requirements. The style chosen will affect the
placement of language elements like braces, function declarations and
comments. You can choose a style interactively by typing C-c . and
pressing the space bar at the prompt to get a list of supported
styles. C-c . runs the function c-set-style
which applies
to all CC Mode language modes though its name might suggest otherwise. A
few of the the supported styles are listed below.
The default style in XEmacs is “gnu” except for Java mode where it
is the “java” style (this is governed by the variable
c-default-style
).
The styles included in CC Mode all use a buffer local variable called
c-basic-offset
as the basic indentation level (this buffer local
variable is used in all CC Mode language modes though its name might
suggest otherwise). All indentation is, by default, expressed in
multiples of c-basic-offset
.
Each style defines a default value for c-basic-offset
, for the
“gnu” style sets it to 2. A very common customization scenario is
where a user wants to use an existing style but with a different basic
offset value. An easy way to do this is to set c-basic-offset
in
the language mode hook after selecting the chosen style.
For example, a user might want to follow a local coding convention of using the “k&r” style for C code with indentation in two columns multiples (instead of the five column default provided by the CC Mode “k&r” style). This can be achieved with the following code in the initialization file (see section The Init File)
(defun my-c-mode-hook () (c-set-style "k&r") (setq c-basic-offset 2)) (add-hook 'c-mode-hook 'my-c-mode-hook) |
Most customizations for indentation in various CC modes can be
accomplished by choosing a style and then choosing value for
c-basic-offset
that meets the local coding convention. CC Mode
has a very customizable indentation engine and a further discussion is
really beyond the scope of this manual. See (cc-mode)Indentation Engine section ‘Indentation Engine’ in The CC Mode Manual.
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Fortran mode provides special motion commands for Fortran statements and subprograms, and indentation commands that understand Fortran conventions of nesting, line numbers, and continuation statements.
Special commands for comments are provided because Fortran comments are unlike those of other languages.
Built-in abbrevs optionally save typing when you insert Fortran keywords.
Use M-x fortran-mode to switch to this major mode. Doing so calls
the value of fortran-mode-hook
as a function of no arguments if
that variable has a non-nil
value.
21.13.1 Motion Commands | Moving point by statements or subprograms. | |
21.13.2 Fortran Indentation | Indentation commands for Fortran. | |
21.13.3 Comments | Inserting and aligning comments. | |
21.13.4 Columns | Measuring columns for valid Fortran. | |
21.13.5 Fortran Keyword Abbrevs | Built-in abbrevs for Fortran keywords. |
Fortran mode was contributed by Michael Prange.
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Fortran mode provides special commands to move by subprograms (functions and subroutines) and by statements. There is also a command to put the region around one subprogram, which is convenient for killing it or moving it.
Move to beginning of subprogram
(beginning-of-fortran-subprogram
).
Move to end of subprogram (end-of-fortran-subprogram
).
Put point at beginning of subprogram and mark at end
(mark-fortran-subprogram
).
Move to beginning of current or next statement
(fortran-next-
).
statement
Move to beginning of current or previous statement
(fortran-
).
previous-statement
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Special commands and features are available for indenting Fortran code. They make sure various syntactic entities (line numbers, comment line indicators, and continuation line flags) appear in the columns that are required for standard Fortran.
21.13.2.1 Fortran Indentation Commands | Commands for indenting Fortran. | |
21.13.2.2 Line Numbers and Continuation | How line numbers auto-indent. | |
21.13.2.3 Syntactic Conventions | Conventions you must obey to avoid trouble. | |
21.13.2.4 Variables for Fortran Indentation | Variables controlling Fortran indent style. |
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Indent the current line (fortran-indent-line
).
Break the current line and set up a continuation line.
Indent all the lines of the subprogram point is in
(fortran-indent-subprogram
).
<TAB> is redefined by Fortran mode to reindent the current line for
Fortran (fortran-indent-line
). Line numbers and continuation
markers are indented to their required columns, and the body of the
statement is independently indented, based on its nesting in the program.
The key C-M-q is redefined as fortran-indent-subprogram
, a
command that reindents all the lines of the Fortran subprogram (function or
subroutine) containing point.
The key M-<LFD> is redefined as fortran-split-line
, a
command to split a line in the appropriate fashion for Fortran. In a
non-comment line, the second half becomes a continuation line and is
indented accordingly. In a comment line, both halves become separate
comment lines.
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If a number is the first non-whitespace in the line, it is assumed to be a line number and is moved to columns 0 through 4. (Columns are always counted from 0 in XEmacs.) If the text on the line starts with the conventional Fortran continuation marker ‘$’, it is moved to column 5. If the text begins with any non whitespace character in column 5, it is assumed to be an unconventional continuation marker and remains in column 5.
Line numbers of four digits or less are normally indented one space.
This amount is controlled by the variable fortran-line-number-indent
,
which is the maximum indentation a line number can have. Line numbers
are indented to right-justify them to end in column 4 unless that would
require more than the maximum indentation. The default value of the
variable is 1.
Simply inserting a line number is enough to indent it according to these
rules. As each digit is inserted, the indentation is recomputed. To turn
off this feature, set the variable fortran-electric-line-number
to
nil
. Then inserting line numbers is like inserting anything else.
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Fortran mode assumes that you follow certain conventions that simplify the task of understanding a Fortran program well enough to indent it properly:
fortran-continuation-char
.
By default, this character is ‘$’.
If you fail to follow these conventions, the indentation commands may indent some lines unaesthetically. However, a correct Fortran program will retain its meaning when reindented even if the conventions are not followed.
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Several additional variables control how Fortran indentation works.
fortran-do-indent
Extra indentation within each level of ‘do’ statement (the default is 3).
fortran-if-indent
Extra indentation within each level of ‘if’ statement (the default is 3).
fortran-continuation-indent
Extra indentation for bodies of continuation lines (the default is 5).
fortran-check-all-num-for-matching-do
If this is nil
, indentation assumes that each ‘do’
statement ends on a ‘continue’ statement. Therefore, when
computing indentation for a statement other than ‘continue’, it
can save time by not checking for a ‘do’ statement ending there.
If this is non-nil
, indenting any numbered statement must check
for a ‘do’ that ends there. The default is nil
.
fortran-minimum-statement-indent
Minimum indentation for Fortran statements. For standard Fortran, this is 6. Statement bodies are always indented at least this much.
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The usual Emacs comment commands assume that a comment can follow a line of code. In Fortran, the standard comment syntax requires an entire line to be just a comment. Therefore, Fortran mode replaces the standard Emacs comment commands and defines some new variables.
Fortran mode can also handle a non-standard comment syntax where comments
start with ‘!’ and can follow other text. Because only some Fortran
compilers accept this syntax, Fortran mode will not insert such comments
unless you have specified to do so in advance by setting the variable
comment-start
to ‘"!"’ (see section Variables).
Align comment or insert new comment (fortran-comment-indent
).
Applies to nonstandard ‘!’ comments only.
Turn all lines of the region into comments, or (with arg)
turn them back into real code (fortran-comment-region
).
M-; in Fortran mode is redefined as the command
fortran-comment-indent
. Like the usual M-; command,
it recognizes an existing comment and aligns its text appropriately.
If there is no existing comment, a comment is inserted and aligned.
Inserting and aligning comments is not the same in Fortran mode as in other modes. When a new comment must be inserted, a full-line comment is inserted if the current line is blank. On a non-blank line, a non-standard ‘!’ comment is inserted if you previously specified you wanted to use them. Otherwise a full-line comment is inserted on a new line before the current line.
Non-standard ‘!’ comments are aligned like comments in other
languages, but full-line comments are aligned differently. In a
standard full-line comment, the comment delimiter itself must always
appear in column zero. What can be aligned is the text within the
comment. You can choose from three styles of alignment by setting the
variable fortran-comment-indent-style
to one of these values:
fixed
The text is aligned at a fixed column, which is the value of
fortran-comment-line-column
. This is the default.
relative
The text is aligned as if it were a line of code, but with an
additional fortran-comment-line-column
columns of indentation.
nil
Text in full-line columns is not moved automatically.
You can also specify the character to be used to indent within
full-line comments by setting the variable fortran-comment-indent-char
to the character you want to use.
Fortran mode introduces two variables comment-line-start
and
comment-line-start-skip
, which do for full-line comments what
comment-start
and comment-start-skip
do for
ordinary text-following comments. Normally these are set properly by
Fortran mode, so you do not need to change them.
The normal Emacs comment command C-x ; has not been redefined. It can therefore be used if you use ‘!’ comments, but is useless in Fortran mode otherwise.
The command C-c ; (fortran-comment-region
) turns all the
lines of the region into comments by inserting the string ‘C$$$’ at
the front of each one. With a numeric arg, the region is turned back into
live code by deleting ‘C$$$’ from the front of each line. You can
control the string used for the comments by setting the variable
fortran-comment-region
. Note that here we have an example of a
command and a variable with the same name; the two uses of the name never
conflict because in Lisp and in Emacs it is always clear from the context
which one is referred to.
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Displays a “column ruler” momentarily above the current line
(fortran-column-ruler
).
Splits the current window horizontally so that it is 72 columns wide.
This may help you avoid going over that limit (fortran-window-create
).
The command C-c C-r (fortran-column-ruler
) shows a column
ruler above the current line. The comment ruler consists of two lines
of text that show you the locations of columns with special significance
in Fortran programs. Square brackets show the limits of the columns for
line numbers, and curly brackets show the limits of the columns for the
statement body. Column numbers appear above them.
Note that the column numbers count from zero, as always in XEmacs. As a result, the numbers may not be those you are familiar with; but the actual positions in the line are standard Fortran.
The text used to display the column ruler is the value of the variable
fortran-comment-ruler
. By changing this variable, you can change
the display.
For even more help, use C-c C-w (fortran-window-create
), a
command which splits the current window horizontally, resulting in a window 72
columns wide. When you edit in this window, you can immediately see
when a line gets too wide to be correct Fortran.
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Fortran mode provides many built-in abbrevs for common keywords and declarations. These are the same sort of abbrevs that you can define yourself. To use them, you must turn on Abbrev mode. see section Abbrevs.
The built-in abbrevs are unusual in one way: they all start with a semicolon. You cannot normally use semicolon in an abbrev, but Fortran mode makes this possible by changing the syntax of semicolon to “word constituent”.
For example, one built-in Fortran abbrev is ‘;c’ for ‘continue’. If you insert ‘;c’ and then insert a punctuation character such as a space or a newline, the ‘;c’ changes automatically to ‘continue’, provided Abbrev mode is enabled.
Type ‘;?’ or ‘;C-h’ to display a list of all built-in Fortran abbrevs and what they stand for.
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Asm mode is a major mode for editing files of assembler code. It defines these commands:
tab-to-tab-stop
.
Insert a newline and then indent using tab-to-tab-stop
.
Insert a colon and then remove the indentation from before the label
preceding colon. Then do tab-to-tab-stop
.
Insert or align a comment.
The variable asm-comment-char
specifies which character
starts comments in assembler syntax.
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