@c -*-texinfo-*-
@c This is part of the GNU Emacs Lisp Reference Manual.
-@c Copyright (C) 1990, 1991, 1992, 1993, 1994 Free Software Foundation, Inc.
+@c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999
+@c Free Software Foundation, Inc.
@c See the file elisp.texi for copying conditions.
@setfilename ../info/buffers
@node Buffers, Windows, Backups and Auto-Saving, Top
A @dfn{buffer} is a Lisp object containing text to be edited. Buffers
are used to hold the contents of files that are being visited; there may
also be buffers that are not visiting files. While several buffers may
-exist at one time, exactly one buffer is designated the @dfn{current
+exist at one time, only one buffer is designated the @dfn{current
buffer} at any time. Most editing commands act on the contents of the
current buffer. Each buffer, including the current buffer, may or may
not be displayed in any windows.
@menu
* Buffer Basics:: What is a buffer?
* Current Buffer:: Designating a buffer as current
- so primitives will access its contents.
+ so that primitives will access its contents.
* Buffer Names:: Accessing and changing buffer names.
* Buffer File Name:: The buffer file name indicates which file is visited.
* Buffer Modification:: A buffer is @dfn{modified} if it needs to be saved.
* Creating Buffers:: Functions that create buffers.
* Killing Buffers:: Buffers exist until explicitly killed.
* Indirect Buffers:: An indirect buffer shares text with some other buffer.
+* Buffer Gap:: The gap in the buffer.
@end menu
@node Buffer Basics
@comment node-name, next, previous, up
@section Buffer Basics
-@ifinfo
+@ifnottex
A @dfn{buffer} is a Lisp object containing text to be edited. Buffers
are used to hold the contents of files that are being visited; there may
-also be buffers that are not visiting files. While several buffers may
-exist at one time, exactly one buffer is designated the @dfn{current
+also be buffers that are not visiting files. Although several buffers
+normally exist, only one buffer is designated the @dfn{current
buffer} at any time. Most editing commands act on the contents of the
current buffer. Each buffer, including the current buffer, may or may
not be displayed in any windows.
-@end ifinfo
+@end ifnottex
Buffers in Emacs editing are objects that have distinct names and hold
text that can be edited. Buffers appear to Lisp programs as a special
-data type. You can think of the contents of a buffer as an extendable
-string; insertions and deletions may occur in any part of the buffer.
-@xref{Text}.
+data type. You can think of the contents of a buffer as a string that
+you can extend; insertions and deletions may occur in any part of the
+buffer. @xref{Text}.
A Lisp buffer object contains numerous pieces of information. Some of
this information is directly accessible to the programmer through
for examining or changing text in a buffer operate implicitly on the
current buffer (@pxref{Text}). Normally the buffer that is displayed on
the screen in the selected window is the current buffer, but this is not
-always so: a Lisp program can designate any buffer as current
-temporarily in order to operate on its contents, without changing what
-is displayed on the screen.
+always so: a Lisp program can temporarily designate any buffer as
+current in order to operate on its contents, without changing what is
+displayed on the screen.
The way to designate a current buffer in a Lisp program is by calling
@code{set-buffer}. The specified buffer remains current until a new one
Emacs reads a command is the buffer that the command will apply to.
(@xref{Command Loop}.) Therefore, @code{set-buffer} is not the way to
switch visibly to a different buffer so that the user can edit it. For
-this, you must use the functions described in @ref{Displaying Buffers}.
+that, you must use the functions described in @ref{Displaying Buffers}.
- However, Lisp functions that change to a different current buffer
+ @strong{Note:} Lisp functions that change to a different current buffer
should not depend on the command loop to set it back afterwards.
Editing commands written in Emacs Lisp can be called from other programs
-as well as from the command loop. It is convenient for the caller if
+as well as from the command loop; it is convenient for the caller if
the subroutine does not change which buffer is current (unless, of
course, that is the subroutine's purpose). Therefore, you should
-normally use @code{set-buffer} within a @code{save-excursion} that will
-restore the current buffer when your function is done
-(@pxref{Excursions}). Here is an example, the code for the command
-@code{append-to-buffer} (with the documentation string abridged):
+normally use @code{set-buffer} within a @code{save-current-buffer} or
+@code{save-excursion} (@pxref{Excursions}) form that will restore the
+current buffer when your function is done. Here is an example, the
+code for the command @code{append-to-buffer} (with the documentation
+string abridged):
@example
@group
@dots{}"
(interactive "BAppend to buffer: \nr")
(let ((oldbuf (current-buffer)))
- (save-excursion
+ (save-current-buffer
(set-buffer (get-buffer-create buffer))
(insert-buffer-substring oldbuf start end))))
@end group
@end example
@noindent
-This function binds a local variable to the current buffer, and then
-@code{save-excursion} records the values of point, the mark, and the
-original buffer. Next, @code{set-buffer} makes another buffer current.
-Finally, @code{insert-buffer-substring} copies the string from the
-original current buffer to the new current buffer.
+This function binds a local variable to record the current buffer, and
+then @code{save-current-buffer} arranges to make it current again.
+Next, @code{set-buffer} makes the specified buffer current. Finally,
+@code{insert-buffer-substring} copies the string from the original
+current buffer to the specified (and now current) buffer.
If the buffer appended to happens to be displayed in some window,
the next redisplay will show how its text has changed. Otherwise, you
binding's scope. Otherwise you might bind it in one buffer and unbind
it in another! There are two ways to do this. In simple cases, you may
see that nothing ever changes the current buffer within the scope of the
-binding. Otherwise, use @code{save-excursion} to make sure that the
-buffer current at the beginning is current again whenever the variable
-is unbound.
+binding. Otherwise, use @code{save-current-buffer} or
+@code{save-excursion} to make sure that the buffer current at the
+beginning is current again whenever the variable is unbound.
- It is not reliable to change the current buffer back with
-@code{set-buffer}, because that won't do the job if a quit happens while
-the wrong buffer is current. Here is what @emph{not} to do:
+ Do not rely on using @code{set-buffer} to change the current buffer
+back, because that won't do the job if a quit happens while the wrong
+buffer is current. Here is what @emph{not} to do:
@example
@group
@end example
@noindent
-Using @code{save-excursion}, as shown below, handles quitting, errors,
-and @code{throw}, as well as ordinary evaluation.
+Using @code{save-current-buffer}, as shown here, handles quitting,
+errors, and @code{throw}, as well as ordinary evaluation.
@example
@group
(let (buffer-read-only)
- (save-excursion
+ (save-current-buffer
(set-buffer @dots{})
@dots{}))
@end group
@end defun
@defun set-buffer buffer-or-name
-This function makes @var{buffer-or-name} the current buffer. It does
-not display the buffer in the currently selected window or in any other
-window, so the user cannot necessarily see the buffer. But Lisp
-programs can in any case work on it.
+This function makes @var{buffer-or-name} the current buffer. This does
+not display the buffer in any window, so the user cannot necessarily see
+the buffer. But Lisp programs will now operate on it.
This function returns the buffer identified by @var{buffer-or-name}.
An error is signaled if @var{buffer-or-name} does not identify an
existing buffer.
@end defun
+@defspec save-current-buffer body...
+The @code{save-current-buffer} macro saves the identity of the current
+buffer, evaluates the @var{body} forms, and finally restores that buffer
+as current. The return value is the value of the last form in
+@var{body}. The current buffer is restored even in case of an abnormal
+exit via @code{throw} or error (@pxref{Nonlocal Exits}).
+
+If the buffer that used to be current has been killed by the time of
+exit from @code{save-current-buffer}, then it is not made current again,
+of course. Instead, whichever buffer was current just before exit
+remains current.
+@end defspec
+
+@defmac with-current-buffer buffer body...
+The @code{with-current-buffer} macro saves the identity of the current
+buffer, makes @var{buffer} current, evaluates the @var{body} forms, and
+finally restores the buffer. The return value is the value of the last
+form in @var{body}. The current buffer is restored even in case of an
+abnormal exit via @code{throw} or error (@pxref{Nonlocal Exits}).
+@end defmac
+
+@defmac with-temp-buffer body...
+The @code{with-temp-buffer} macro evaluates the @var{body} forms
+with a temporary buffer as the current buffer. It saves the identity of
+the current buffer, creates a temporary buffer and makes it current,
+evaluates the @var{body} forms, and finally restores the previous
+current buffer while killing the temporary buffer.
+
+The return value is the value of the last form in @var{body}. You can
+return the contents of the temporary buffer by using
+@code{(buffer-string)} as the last form.
+
+The current buffer is restored even in case of an abnormal exit via
+@code{throw} or error (@pxref{Nonlocal Exits}).
+@end defmac
+
+See also @code{with-temp-file} in @ref{Writing to Files}.
+
@node Buffer Names
@section Buffer Names
@cindex buffer names
Buffers that are ephemeral and generally uninteresting to the user
have names starting with a space, so that the @code{list-buffers} and
-@code{buffer-menu} commands don't mention them. A name starting with
+@code{buffer-menu} commands don't mention them (but if such a buffer
+visits a file, it @strong{is} mentioned). A name starting with
space also initially disables recording undo information; see
@ref{Undo}.
@deffn Command rename-buffer newname &optional unique
This function renames the current buffer to @var{newname}. An error
is signaled if @var{newname} is not a string, or if there is already a
-buffer with that name. The function returns @code{nil}.
+buffer with that name. The function returns @var{newname}.
@c Emacs 19 feature
Ordinarily, @code{rename-buffer} signals an error if @var{newname} is
already in use. However, if @var{unique} is non-@code{nil}, it modifies
@var{newname} to make a name that is not in use. Interactively, you can
make @var{unique} non-@code{nil} with a numeric prefix argument.
-
-One application of this command is to rename the @samp{*shell*} buffer
-to some other name, thus making it possible to create a second shell
-buffer under the name @samp{*shell*}.
+(This is how the command @code{rename-uniquely} is implemented.)
@end deffn
@defun get-buffer buffer-or-name
This function returns the buffer specified by @var{buffer-or-name}.
If @var{buffer-or-name} is a string and there is no buffer with that
name, the value is @code{nil}. If @var{buffer-or-name} is a buffer, it
-is returned as given. (That is not very useful, so the argument is usually
-a name.) For example:
+is returned as given; that is not very useful, so the argument is usually
+a name. For example:
@example
@group
@end defun
@c Emacs 19 feature
-@defun generate-new-buffer-name starting-name
+@defun generate-new-buffer-name starting-name &rest ignore
This function returns a name that would be unique for a new buffer---but
does not create the buffer. It starts with @var{starting-name}, and
produces a name not currently in use for any buffer by appending a
number inside of @samp{<@dots{}>}.
+If the optional second argument @var{ignore} is non-@code{nil}, it
+should be a string; it makes a difference if it is a name in the
+sequence of names to be tried. That name will be considered acceptable,
+if it is tried, even if a buffer with that name exists. Thus, if
+buffers named @samp{foo}, @samp{foo<2>}, @samp{foo<3>} and @samp{foo<4>}
+exist,
+
+@example
+(generate-new-buffer-name "foo")
+ @result{} "foo<5>"
+(generate-new-buffer-name "foo" "foo<3>")
+ @result{} "foo<3>"
+(generate-new-buffer-name "foo" "foo<6>")
+ @result{} "foo<5>"
+@end example
+
See the related function @code{generate-new-buffer} in @ref{Creating
Buffers}.
@end defun
@defvar buffer-file-name
This buffer-local variable contains the name of the file being visited
in the current buffer, or @code{nil} if it is not visiting a file. It
-is a permanent local, unaffected by @code{kill-local-variables}.
+is a permanent local variable, unaffected by
+@code{kill-all-local-variables}.
@example
@group
@end example
It is risky to change this variable's value without doing various other
-things. See the definition of @code{set-visited-file-name} in
-@file{files.el}; some of the things done there, such as changing the
-buffer name, are not strictly necessary, but others are essential to
-avoid confusing Emacs.
+things. Normally it is better to use @code{set-visited-file-name} (see
+below); some of the things done there, such as changing the buffer name,
+are not strictly necessary, but others are essential to avoid confusing
+Emacs.
@end defvar
@defvar buffer-file-truename
This buffer-local variable holds the truename of the file visited in the
current buffer, or @code{nil} if no file is visited. It is a permanent
-local, unaffected by @code{kill-local-variables}. @xref{Truenames}.
+local, unaffected by @code{kill-all-local-variables}. @xref{Truenames}.
@end defvar
@defvar buffer-file-number
This buffer-local variable holds the file number and directory device
number of the file visited in the current buffer, or @code{nil} if no
file or a nonexistent file is visited. It is a permanent local,
-unaffected by @code{kill-local-variables}. @xref{Truenames}.
+unaffected by @code{kill-all-local-variables}.
The value is normally a list of the form @code{(@var{filenum}
@var{devnum})}. This pair of numbers uniquely identifies the file among
such buffer in the buffer list.
@end defun
-@deffn Command set-visited-file-name filename
+@deffn Command set-visited-file-name filename &optional no-query along-with-file
If @var{filename} is a non-empty string, this function changes the
-name of the file visited in current buffer to @var{filename}. (If the
+name of the file visited in the current buffer to @var{filename}. (If the
buffer had no visited file, this gives it one.) The @emph{next time}
the buffer is saved it will go in the newly-specified file. This
command marks the buffer as modified, since it does not (as far as Emacs
``no visited file''. In this case, @code{set-visited-file-name} marks
the buffer as having no visited file.
+Normally, this function asks the user for confirmation if the specified
+file already exists. If @var{no-query} is non-@code{nil}, that prevents
+asking this question.
+
+If @var{along-with-file} is non-@code{nil}, that means to assume that the
+former visited file has been renamed to @var{filename}.
+
@c Wordy to avoid overfull hbox. --rjc 16mar92
When the function @code{set-visited-file-name} is called interactively, it
prompts for @var{filename} in the minibuffer.
-
-See also @code{clear-visited-file-modtime} and
-@code{verify-visited-file-modtime} in @ref{Buffer Modification}.
@end deffn
@defvar list-buffers-directory
-This buffer-local variable records a string to display in a buffer
-listing in place of the visited file name, for buffers that don't have a
-visited file name. Dired buffers use this variable.
+This buffer-local variable specifies a string to display in a buffer
+listing where the visited file name would go, for buffers that don't
+have a visited file name. Dired buffers use this variable.
@end defvar
@node Buffer Modification
@end defun
@deffn Command not-modified
-This command marks the current buffer as unmodified, and not needing
-to be saved. Don't use this function in programs, since it prints a
-message in the echo area; use @code{set-buffer-modified-p} (above) instead.
+This command marks the current buffer as unmodified, and not needing to
+be saved. With prefix arg, it marks the buffer as modified, so that it
+will be saved at the next suitable occasion.
+
+Don't use this function in programs, since it prints a message in the
+echo area; use @code{set-buffer-modified-p} (above) instead.
@end deffn
@c Emacs 19 feature
@defun buffer-modified-tick &optional buffer
-This function returns @var{buffer}`s modification-count. This is a
+This function returns @var{buffer}'s modification-count. This is a
counter that increments every time the buffer is modified. If
@var{buffer} is @code{nil} (or omitted), the current buffer is used.
@end defun
@item
A buffer visiting a write-protected file is normally read-only.
-Here, the purpose is to show the user that editing the buffer with the
+Here, the purpose is to inform the user that editing the buffer with the
aim of saving it in the file may be futile or undesirable. The user who
wants to change the buffer text despite this can do so after clearing
the read-only flag with @kbd{C-x C-q}.
@item
Modes such as Dired and Rmail make buffers read-only when altering the
-contents with the usual editing commands is probably a mistake.
+contents with the usual editing commands would probably be a mistake.
The special commands of these modes bind @code{buffer-read-only} to
@code{nil} (with @code{let}) or bind @code{inhibit-read-only} to
-@code{t} around the places where they change the text.
+@code{t} around the places where they themselves change the text.
@end itemize
@defvar buffer-read-only
@deffn Command toggle-read-only
This command changes whether the current buffer is read-only. It is
-intended for interactive use; don't use it in programs. At any given
+intended for interactive use; do not use it in programs. At any given
point in a program, you should know whether you want the read-only flag
on or off; so you can set @code{buffer-read-only} explicitly to the
proper value, @code{t} or @code{nil}.
@cindex buffer list
The @dfn{buffer list} is a list of all live buffers. Creating a
-buffer adds it to this list, and killing a buffer deletes it. The order
+buffer adds it to this list, and killing a buffer excises it. The order
of the buffers in the list is based primarily on how recently each
buffer has been displayed in the selected window. Buffers move to the
front of the list when they are selected and to the end when they are
-buried. Several functions, notably @code{other-buffer}, use this
-ordering. A buffer list displayed for the user also follows this order.
-
-@defun buffer-list
-This function returns a list of all buffers, including those whose names
-begin with a space. The elements are actual buffers, not their names.
+buried (see @code{bury-buffer}, below). Several functions, notably
+@code{other-buffer}, use this ordering. A buffer list displayed for the
+user also follows this order.
+
+ In addition to the fundamental Emacs buffer list, each frame has its
+own version of the buffer list, in which the buffers that have been
+selected in that frame come first, starting with the buffers most
+recently selected @emph{in that frame}. (This order is recorded in
+@var{frame}'s @code{buffer-list} frame parameter; see @ref{Window Frame
+Parameters}.) The buffers that were never selected in @var{frame} come
+afterward, ordered according to the fundamental Emacs buffer list.
+
+@defun buffer-list &optional frame
+This function returns the buffer list, including all buffers, even those
+whose names begin with a space. The elements are actual buffers, not
+their names.
+
+If @var{frame} is a frame, this returns @var{frame}'s buffer list. If
+@var{frame} is @code{nil}, the fundamental Emacs buffer list is used:
+all the buffers appear in order of most recent selection, regardless of
+which frames they were selected in.
@example
@group
"buffer.c" "*Help*" "TAGS")
@end group
@end example
-
-This list is a copy of a list used inside Emacs; modifying it has no
-effect on the ordering of buffers.
@end defun
-@defun other-buffer &optional buffer-or-name visible-ok
+ The list that @code{buffer-list} returns is constructed specifically
+by @code{buffer-list}; it is not an internal Emacs data structure, and
+modifying it has no effect on the order of buffers. If you want to
+change the order of buffers in the frame-independent buffer list, here
+is an easy way:
+
+@example
+(defun reorder-buffer-list (new-list)
+ (while new-list
+ (bury-buffer (car new-list))
+ (setq new-list (cdr new-list))))
+@end example
+
+ With this method, you can specify any order for the list, but there is
+no danger of losing a buffer or adding something that is not a valid
+live buffer.
+
+ To change the order or value of a frame's buffer list, set the frame's
+@code{buffer-list} frame parameter with @code{modify-frame-parameters}
+(@pxref{Parameter Access}).
+
+@defun other-buffer &optional buffer visible-ok frame
This function returns the first buffer in the buffer list other than
-@var{buffer-or-name}. Usually this is the buffer most recently shown in
-the selected window, aside from @var{buffer-or-name}. Buffers whose
-names start with a space are not considered.
+@var{buffer}. Usually this is the buffer selected most recently (in
+frame @var{frame} or else the currently selected frame, @pxref{Input
+Focus}), aside from @var{buffer}. Buffers whose names start with a
+space are not considered at all.
-If @var{buffer-or-name} is not supplied (or if it is not a buffer),
-then @code{other-buffer} returns the first buffer on the buffer list
-that is not visible in any window in a visible frame.
+If @var{buffer} is not supplied (or if it is not a buffer), then
+@code{other-buffer} returns the first buffer in the selected frame's
+buffer list that is not now visible in any window in a visible frame.
-If the selected frame has a non-@code{nil} @code{buffer-predicate}
-parameter, then @code{other-buffer} uses that predicate to decide which
-buffers to consider. It calls the predicate once for each buffer, and
-if the value is @code{nil}, that buffer is ignored. @xref{X Frame
-Parameters}.
+If @var{frame} has a non-@code{nil} @code{buffer-predicate} parameter,
+then @code{other-buffer} uses that predicate to decide which buffers to
+consider. It calls the predicate once for each buffer, and if the value
+is @code{nil}, that buffer is ignored. @xref{Window Frame Parameters}.
@c Emacs 19 feature
If @var{visible-ok} is @code{nil}, @code{other-buffer} avoids returning
@end defun
@deffn Command bury-buffer &optional buffer-or-name
-This function puts @var{buffer-or-name} at the end of the buffer list
+This function puts @var{buffer-or-name} at the end of the buffer list,
without changing the order of any of the other buffers on the list.
This buffer therefore becomes the least desirable candidate for
@code{other-buffer} to return.
+@code{bury-buffer} operates on each frame's @code{buffer-list} parameter
+as well as the frame-independent Emacs buffer list; therefore, the
+buffer that you bury will come last in the value of @code{(buffer-list
+@var{frame})} and in the value of @code{(buffer-list nil)}.
+
If @var{buffer-or-name} is @code{nil} or omitted, this means to bury the
current buffer. In addition, if the buffer is displayed in the selected
window, this switches to some other buffer (obtained using
@code{other-buffer}) in the selected window. But if the buffer is
displayed in some other window, it remains displayed there.
-If you wish to replace a buffer in all the windows that display it, use
+To replace a buffer in all the windows that display it, use
@code{replace-buffer-in-windows}. @xref{Buffers and Windows}.
@end deffn
The buffer object for the buffer that has been killed remains in
existence as long as anything refers to it, but it is specially marked
so that you cannot make it current or display it. Killed buffers retain
-their identity, however; two distinct buffers, when killed, remain
-distinct according to @code{eq}.
+their identity, however; if you kill two distinct buffers, they remain
+distinct according to @code{eq} although both are dead.
If you kill a buffer that is current or displayed in a window, Emacs
automatically selects or displays some other buffer instead. This means
@deffn Command kill-buffer buffer-or-name
This function kills the buffer @var{buffer-or-name}, freeing all its
-memory for use as space for other buffers. (Emacs version 18 and older
-was unable to return the memory to the operating system.) It returns
-@code{nil}.
+memory for other uses or to be returned to the operating system. It
+returns @code{nil}.
Any processes that have this buffer as the @code{process-buffer} are
sent the @code{SIGHUP} signal, which normally causes them to terminate.
(The basic meaning of @code{SIGHUP} is that a dialup line has been
-disconnected.) @xref{Deleting Processes}.
+disconnected.) @xref{Signals to Processes}.
If the buffer is visiting a file and contains unsaved changes,
@code{kill-buffer} asks the user to confirm before the buffer is killed.
After confirming unsaved changes, @code{kill-buffer} calls the functions
in the list @code{kill-buffer-query-functions}, in order of appearance,
with no arguments. The buffer being killed is the current buffer when
-they are called. The idea is that these functions ask for confirmation
-from the user for various nonstandard reasons. If any of them returns
-@code{nil}, @code{kill-buffer} spares the buffer's life.
+they are called. The idea of this feature is that these functions will
+ask for confirmation from the user. If any of them returns @code{nil},
+@code{kill-buffer} spares the buffer's life.
@end defvar
@defvar kill-buffer-hook
in the other. This includes the text properties as well as the characters
themselves.
- But in all other respects, the indirect buffer and its base buffer are
+ In all other respects, the indirect buffer and its base buffer are
completely separate. They have different names, different values of
point, different narrowing, different markers and overlays (though
inserting or deleting text in either buffer relocates the markers and
-overlays for both), different major modes, and different local
+overlays for both), different major modes, and different buffer-local
variables.
An indirect buffer cannot visit a file, but its base buffer can. If
-you try to save the indirect buffer, that actually works by saving the
-base buffer.
+you try to save the indirect buffer, that actually saves the base
+buffer.
Killing an indirect buffer has no effect on its base buffer. Killing
the base buffer effectively kills the indirect buffer in that it cannot
another buffer, which is never an indirect buffer.
@end defun
+@node Buffer Gap
+@section The Buffer Gap
+
+ Emacs buffers are implemented using an invisible @dfn{gap} to make
+insertion and deletion faster. Insertion works by filling in part of
+the gap, and deletion adds to the gap. Of course, this means that the
+gap must first be moved to the locus of the insertion or deletion.
+Emacs moves the gap only when you try to insert or delete. This is why
+your first editing command in one part of a large buffer, after
+previously editing in another far-away part, sometimes involves a
+noticeable delay.
+
+ This mechanism works invisibly, and Lisp code should never be affected
+by the gap's current location, but these functions are available for
+getting information about the gap status.
+
+@defun gap-position
+This function returns the current gap position in the current buffer.
+@end defun
+
+@defun gap-size
+This function returns the current gap size of the current buffer.
+@end defun
HCoop / bpt / emacs.git / blobdiff