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diff --git a/lispref/backups.texi b/lispref/backups.texi new file mode 100644 index 00000000000..57108105e0b --- /dev/null +++ b/lispref/backups.texi @@ -0,0 +1,621 @@ +@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 See the file elisp.texi for copying conditions. +@setfilename ../info/backups +@node Backups and Auto-Saving, Buffers, Files, Top +@chapter Backups and Auto-Saving + + Backup files and auto-save files are two methods by which Emacs tries +to protect the user from the consequences of crashes or of the user's +own errors. Auto-saving preserves the text from earlier in the current +editing session; backup files preserve file contents prior to the +current session. + +@menu +* Backup Files:: How backup files are made; how their names are chosen. +* Auto-Saving:: How auto-save files are made; how their names are chosen. +* Reverting:: @code{revert-buffer}, and how to customize what it does. +@end menu + +@node Backup Files, Auto-Saving, Backups and Auto-Saving, Backups and Auto-Saving +@section Backup Files +@cindex backup file + + A @dfn{backup file} is a copy of the old contents of a file you are +editing. Emacs makes a backup file the first time you save a buffer +into its visited file. Normally, this means that the backup file +contains the contents of the file as it was before the current editing +session. The contents of the backup file normally remain unchanged once +it exists. + + Backups are usually made by renaming the visited file to a new name. +Optionally, you can specify that backup files should be made by copying +the visited file. This choice makes a difference for files with +multiple names; it also can affect whether the edited file remains owned +by the original owner or becomes owned by the user editing it. + + By default, Emacs makes a single backup file for each file edited. +You can alternatively request numbered backups; then each new backup +file gets a new name. You can delete old numbered backups when you +don't want them any more, or Emacs can delete them automatically. + +@menu +* Making Backups:: How Emacs makes backup files, and when. +* Rename or Copy:: Two alternatives: renaming the old file or copying it. +* Numbered Backups:: Keeping multiple backups for each source file. +* Backup Names:: How backup file names are computed; customization. +@end menu + +@node Making Backups, Rename or Copy, Backup Files, Backup Files +@subsection Making Backup Files + +@defun backup-buffer + This function makes a backup of the file visited by the current +buffer, if appropriate. It is called by @code{save-buffer} before +saving the buffer the first time. +@end defun + +@defvar buffer-backed-up + This buffer-local variable indicates whether this buffer's file has +been backed up on account of this buffer. If it is non-@code{nil}, then +the backup file has been written. Otherwise, the file should be backed +up when it is next saved (if backup files are enabled). This is a +permanent local; @code{kill-local-variables} does not alter it. +@end defvar + +@defopt make-backup-files + This variable determines whether or not to make backup files. If it +is non-@code{nil}, then Emacs creates a backup of each file when it is +saved for the first time. + + The following example shows how to change the @code{make-backup-files} +variable only in the @file{RMAIL} buffer and not elsewhere. Setting it +@code{nil} stops Emacs from making backups of the @file{RMAIL} file, +which may save disk space. (You would put this code in your +@file{.emacs} file.) + +@smallexample +@group +(add-hook 'rmail-mode-hook + (function (lambda () + (make-local-variable + 'make-backup-files) + (setq make-backup-files nil)))) +@end group +@end smallexample +@end defopt + +@defvar backup-enable-predicate filename +This variable's value is a function to be called on certain occasions to +decide whether a there should be backup files for file name +@var{filename}. If it returns @code{nil}, backups are disabled. +Otherwise, the other variables in this section say whether and how to +make backups. + +The default value is this: + +@example +(lambda (name) + (or (< (length name) 5) + (not (string-equal "/tmp/" + (substring name 0 5))))) +@end example +@end defvar + +@defvar backup-inhibited +If this variable is non-@code{nil}, backups are inhibited. It records +the result of testing @code{backup-enable-predicate} on the visited file +name. It can also coherently be used by other mechanisms that inhibit +backups based on which file is visited. Major modes should not set this +variable. +@end defvar + +@node Rename or Copy, Numbered Backups, Making Backups, Backup Files +@subsection Backup by Renaming or by Copying? +@cindex backup files, how to make them + + There are two ways that Emacs can make a backup file: + +@itemize @bullet +@item +Emacs can rename the original file so that it becomes a backup file, and +then write the buffer being saved into a new file. After this +procedure, any other names (i.e., hard links) of the original file now +refer to the backup file. The new file is owned by the user doing the +editing, and its group is the default for new files written by the user +in that directory. + +@item +Emacs can copy the original file into a backup file, and then overwrite +the original file with new contents. After this procedure, any other +names (i.e., hard links) of the original file still refer to the current +version of the file. The file's owner and group will be unchanged. +@end itemize + + The first method, renaming, is the default. + + The variable @code{backup-by-copying}, if non-@code{nil}, says to use +the second method, which is to copy the original file and overwrite it +with the new buffer contents. The variable @code{file-precious-flag}, +if non-@code{nil}, also has this effect (as a sideline of its main +significance). @xref{Saving Buffers}. + +@defvar backup-by-copying +If this variable is non-@code{nil}, Emacs always makes backup files by +copying. +@end defvar + + The following two variables, when non-@code{nil}, cause the second +method to be used in certain special cases. They have no effect on the +treatment of files that don't fall into the special cases. + +@defvar backup-by-copying-when-linked +If this variable is non-@code{nil}, Emacs makes backups by copying for +files with multiple names (hard links). + +This variable is significant only if @code{backup-by-copying} is +@code{nil}, since copying is always used when that variable is +non-@code{nil}. +@end defvar + +@defvar backup-by-copying-when-mismatch +If this variable is non-@code{nil}, Emacs makes backups by copying in cases +where renaming would change either the owner or the group of the file. + +The value has no effect when renaming would not alter the owner or +group of the file; that is, for files which are owned by the user and +whose group matches the default for a new file created there by the +user. + +This variable is significant only if @code{backup-by-copying} is +@code{nil}, since copying is always used when that variable is +non-@code{nil}. +@end defvar + +@node Numbered Backups, Backup Names, Rename or Copy, Backup Files +@subsection Making and Deleting Numbered Backup Files + + If a file's name is @file{foo}, the names of its numbered backup +versions are @file{foo.~@var{v}~}, for various integers @var{v}, like +this: @file{foo.~1~}, @file{foo.~2~}, @file{foo.~3~}, @dots{}, +@file{foo.~259~}, and so on. + +@defopt version-control +This variable controls whether to make a single non-numbered backup +file or multiple numbered backups. + +@table @asis +@item @code{nil} +Make numbered backups if the visited file already has numbered backups; +otherwise, do not. + +@item @code{never} +Do not make numbered backups. + +@item @var{anything else} +Do make numbered backups. +@end table +@end defopt + + The use of numbered backups ultimately leads to a large number of +backup versions, which must then be deleted. Emacs can do this +automatically. + +@defopt kept-new-versions +The value of this variable is the number of oldest versions to keep +when a new numbered backup is made. The newly made backup is included +in the count. The default value is 2. +@end defopt + +@defopt kept-old-versions +The value of this variable is the number of oldest versions to keep +when a new numbered backup is made. The default value is 2. +@end defopt + + If there are backups numbered 1, 2, 3, 5, and 7, and both of these +variables have the value 2, then the backups numbered 1 and 2 are kept +as old versions and those numbered 5 and 7 are kept as new versions; +backup version 3 is deleted. The function @code{find-backup-file-name} +(@pxref{Backup Names}) is responsible for determining which backup +versions to delete, but does not delete them itself. + +@defopt trim-versions-without-asking +If this variable is non-@code{nil}, then saving a file deletes excess +backup versions silently. Otherwise, it asks the user whether to delete +them. +@end defopt + +@defopt dired-kept-versions +This variable specifies how many of the newest backup versions to keep +in the Dired command @kbd{.} (@code{dired-clean-directory}). That's the +same thing @code{kept-new-versions} does when you make a new backup +file. The default value is 2. +@end defopt + +@node Backup Names, , Numbered Backups, Backup Files +@subsection Naming Backup Files + + The functions in this section are documented mainly because you can +customize the naming conventions for backup files by redefining them. +If you change one, you probably need to change the rest. + +@defun backup-file-name-p filename +This function returns a non-@code{nil} value if @var{filename} is a +possible name for a backup file. A file with the name @var{filename} +need not exist; the function just checks the name. + +@smallexample +@group +(backup-file-name-p "foo") + @result{} nil +@end group +@group +(backup-file-name-p "foo~") + @result{} 3 +@end group +@end smallexample + +The standard definition of this function is as follows: + +@smallexample +@group +(defun backup-file-name-p (file) + "Return non-nil if FILE is a backup file \ +name (numeric or not)..." + (string-match "~$" file)) +@end group +@end smallexample + +@noindent +Thus, the function returns a non-@code{nil} value if the file name ends +with a @samp{~}. (We use a backslash to split the documentation +string's first line into two lines in the text, but produce just one +line in the string itself.) + +This simple expression is placed in a separate function to make it easy +to redefine for customization. +@end defun + +@defun make-backup-file-name filename +This function returns a string which is the name to use for a +non-numbered backup file for file @var{filename}. On Unix, this is just +@var{filename} with a tilde appended. + +The standard definition of this function is as follows: + +@smallexample +@group +(defun make-backup-file-name (file) + "Create the non-numeric backup file name for FILE. +@dots{}" + (concat file "~")) +@end group +@end smallexample + +You can change the backup file naming convention by redefining this +function. The following example redefines @code{make-backup-file-name} +to prepend a @samp{.} as well as appending a tilde: + +@smallexample +@group +(defun make-backup-file-name (filename) + (concat "." filename "~")) +@end group + +@group +(make-backup-file-name "backups.texi") + @result{} ".backups.texi~" +@end group +@end smallexample +@end defun + +@defun find-backup-file-name filename +This function computes the file name for a new backup file for +@var{filename}. It may also propose certain existing backup files for +deletion. @code{find-backup-file-name} returns a list whose @sc{car} is +the name for the new backup file and whose @sc{cdr} is a list of backup +files whose deletion is proposed. + +Two variables, @code{kept-old-versions} and @code{kept-new-versions}, +determine which backup versions should be kept. This function keeps +those versions by excluding them from the @sc{cdr} of the value. +@xref{Numbered Backups}. + +In this example, the value says that @file{~rms/foo.~5~} is the name +to use for the new backup file, and @file{~rms/foo.~3~} is an ``excess'' +version that the caller should consider deleting now. + +@smallexample +@group +(find-backup-file-name "~rms/foo") + @result{} ("~rms/foo.~5~" "~rms/foo.~3~") +@end group +@end smallexample +@end defun + +@c Emacs 19 feature +@defun file-newest-backup filename +This function returns the name of the most recent backup file for +@var{filename}, or @code{nil} that file has no backup files. + +Some file comparison commands use this function in order to compare +a file by default with its most recent backup. +@end defun + +@node Auto-Saving, Reverting, Backup Files, Backups and Auto-Saving +@section Auto-Saving +@cindex auto-saving + + Emacs periodically saves all files that you are visiting; this is +called @dfn{auto-saving}. Auto-saving prevents you from losing more +than a limited amount of work if the system crashes. By default, +auto-saves happen every 300 keystrokes, or after around 30 seconds of +idle time. @xref{Auto-Save, Auto-Save, Auto-Saving: Protection Against +Disasters, emacs, The GNU Emacs Manual}, for information on auto-save +for users. Here we describe the functions used to implement auto-saving +and the variables that control them. + +@defvar buffer-auto-save-file-name +This buffer-local variable is the name of the file used for +auto-saving the current buffer. It is @code{nil} if the buffer +should not be auto-saved. + +@example +@group +buffer-auto-save-file-name +=> "/xcssun/users/rms/lewis/#files.texi#" +@end group +@end example +@end defvar + +@deffn Command auto-save-mode arg +When used interactively without an argument, this command is a toggle +switch: it turns on auto-saving of the current buffer if it is off, and +vice-versa. With an argument @var{arg}, the command turns auto-saving +on if the value of @var{arg} is @code{t}, a nonempty list, or a positive +integer. Otherwise, it turns auto-saving off. +@end deffn + +@defun auto-save-file-name-p filename +This function returns a non-@code{nil} value if @var{filename} is a +string that could be the name of an auto-save file. It works based on +knowledge of the naming convention for auto-save files: a name that +begins and ends with hash marks (@samp{#}) is a possible auto-save file +name. The argument @var{filename} should not contain a directory part. + +@example +@group +(make-auto-save-file-name) + @result{} "/xcssun/users/rms/lewis/#files.texi#" +@end group +@group +(auto-save-file-name-p "#files.texi#") + @result{} 0 +@end group +@group +(auto-save-file-name-p "files.texi") + @result{} nil +@end group +@end example + +The standard definition of this function is as follows: + +@example +@group +(defun auto-save-file-name-p (filename) + "Return non-nil if FILENAME can be yielded by..." + (string-match "^#.*#$" filename)) +@end group +@end example + +This function exists so that you can customize it if you wish to +change the naming convention for auto-save files. If you redefine it, +be sure to redefine the function @code{make-auto-save-file-name} +correspondingly. +@end defun + +@defun make-auto-save-file-name +This function returns the file name to use for auto-saving the current +buffer. This is just the file name with hash marks (@samp{#}) appended +and prepended to it. This function does not look at the variable +@code{auto-save-visited-file-name}; you should check that before calling +this function. + +@example +@group +(make-auto-save-file-name) + @result{} "/xcssun/users/rms/lewis/#backup.texi#" +@end group +@end example + +The standard definition of this function is as follows: + +@example +@group +(defun make-auto-save-file-name () + "Return file name to use for auto-saves \ +of current buffer. +@dots{}" + (if buffer-file-name +@end group +@group + (concat + (file-name-directory buffer-file-name) + "#" + (file-name-nondirectory buffer-file-name) + "#") + (expand-file-name + (concat "#%" (buffer-name) "#")))) +@end group +@end example + +This exists as a separate function so that you can redefine it to +customize the naming convention for auto-save files. Be sure to +change @code{auto-save-file-name-p} in a corresponding way. +@end defun + +@defvar auto-save-visited-file-name +If this variable is non-@code{nil}, Emacs auto-saves buffers in +the files they are visiting. That is, the auto-save is done in the same +file which you are editing. Normally, this variable is @code{nil}, so +auto-save files have distinct names that are created by +@code{make-auto-save-file-name}. + +When you change the value of this variable, the value does not take +effect until the next time auto-save mode is reenabled in any given +buffer. If auto-save mode is already enabled, auto-saves continue to go +in the same file name until @code{auto-save-mode} is called again. +@end defvar + +@defun recent-auto-save-p +This function returns @code{t} if the current buffer has been +auto-saved since the last time it was read in or saved. +@end defun + +@defun set-buffer-auto-saved +This function marks the current buffer as auto-saved. The buffer will +not be auto-saved again until the buffer text is changed again. The +function returns @code{nil}. +@end defun + +@defopt auto-save-interval +The value of this variable is the number of characters that Emacs +reads from the keyboard between auto-saves. Each time this many more +characters are read, auto-saving is done for all buffers in which it is +enabled. +@end defopt + +@defopt auto-save-timeout +The value of this variable is the number of seconds of idle time that +should cause auto-saving. Each time the user pauses for this long, +Emacs auto-saves any buffers that need it. (Actually, the specified +timeout is multiplied by a factor depending on the size of the current +buffer.) +@end defopt + +@defvar auto-save-hook +This normal hook is run whenever an auto-save is about to happen. +@end defvar + +@defopt auto-save-default +If this variable is non-@code{nil}, buffers that are visiting files +have auto-saving enabled by default. Otherwise, they do not. +@end defopt + +@deffn Command do-auto-save &optional no-message +This function auto-saves all buffers that need to be auto-saved. It +saves all buffers for which auto-saving is enabled and that have been +changed since the previous auto-save. + +Normally, if any buffers are auto-saved, a message that says +@samp{Auto-saving...} is displayed in the echo area while auto-saving is +going on. However, if @var{no-message} is non-@code{nil}, the message +is inhibited. +@end deffn + +@defun delete-auto-save-file-if-necessary +This function deletes the current buffer's auto-save file if +@code{delete-auto-save-files} is non-@code{nil}. It is called every +time a buffer is saved. +@end defun + +@defvar delete-auto-save-files +This variable is used by the function +@code{delete-auto-save-file-if-necessary}. If it is non-@code{nil}, +Emacs deletes auto-save files when a true save is done (in the visited +file). This saves disk space and unclutters your directory. +@end defvar + +@defun rename-auto-save-file +This function adjusts the current buffer's auto-save file name if the +visited file name has changed. It also renames an existing auto-save +file. If the visited file name has not changed, this function does +nothing. +@end defun + +@node Reverting, , Auto-Saving, Backups and Auto-Saving +@section Reverting + + If you have made extensive changes to a file and then change your mind +about them, you can get rid of them by reading in the previous version +of the file with the @code{revert-buffer} command. @xref{Reverting, , +Reverting a Buffer, emacs, The GNU Emacs Manual}. + +@deffn Command revert-buffer &optional check-auto-save noconfirm +This command replaces the buffer text with the text of the visited +file on disk. This action undoes all changes since the file was visited +or saved. + +If the argument @var{check-auto-save} is non-@code{nil}, and the +latest auto-save file is more recent than the visited file, +@code{revert-buffer} asks the user whether to use that instead. +Otherwise, it always uses the text of the visited file itself. +Interactively, @var{check-auto-save} is set if there is a numeric prefix +argument. + +Normally, @code{revert-buffer} asks for confirmation before it changes +the buffer; but if the argument @var{noconfirm} is non-@code{nil}, +@code{revert-buffer} does not ask for confirmation. + +Reverting tries to preserve marker positions in the buffer by using the +replacement feature of @code{insert-file-contents}. If there is no +actual difference between the buffer and the file, before reversion, +this preserves all the markers. If reversion does change the buffer, +this preserves the markers in the unchanged text (if any) at the +beginning and end of the buffer. Preserving any additional markers +would be problematical. + +If the value of the @code{revert-buffer-function} variable is +non-@code{nil}, it is called as a function with no arguments to do the +work. +@end deffn + +@defvar revert-buffer-function +The value of this variable is the function to use to revert this +buffer; but if the value of this variable is @code{nil}, then the +@code{revert-buffer} function carries out its default action. Modes +such as Dired mode, in which the text being edited does not consist of a +file's contents but can be regenerated in some other fashion, give this +variable a buffer-local value that is a function to regenerate the +contents. +@end defvar + +@defvar revert-buffer-insert-file-contents-function +The value of this variable, if non-@code{nil}, is the function to use +to insert contents when reverting this buffer. The function receives +two arguments, first the file name to use, and second, @code{t} if the +user has asked to read the auto-save file. +@end defvar + +@defvar before-revert-hook +This normal hook is run by @code{revert-buffer} before actually +inserting the modified contents---but only if +@code{revert-buffer-function} is @code{nil}. + +Font Lock mode uses this hook to record that the buffer contents are no +longer fontified. +@end defvar + +@defvar after-revert-hook +This normal hook is run by @code{revert-buffer} after actually inserting +the modified contents---but only if @code{revert-buffer-function} is +@code{nil}. + +Font Lock mode uses this hook to recompute the fonts for the updated +buffer contents. +@end defvar + +@deffn Command recover-file filename +This function visits @var{filename}, but gets the contents from its +last auto-save file. This is useful after the system has crashed, to +resume editing the same file without losing all the work done in the +previous session. + +An error is signaled if there is no auto-save file for @var{filename}, +or if @var{filename} is newer than its auto-save file. If +@var{filename} does not exist, but its auto-save file does, then the +auto-save file is read as usual. This last situation may occur if you +visited a nonexistent file and never actually saved it. +@end deffn + diff --git a/lispref/buffers.texi b/lispref/buffers.texi new file mode 100644 index 00000000000..6f777d7480c --- /dev/null +++ b/lispref/buffers.texi @@ -0,0 +1,828 @@ +@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 See the file elisp.texi for copying conditions. +@setfilename ../info/buffers +@node Buffers, Windows, Backups and Auto-Saving, Top +@chapter Buffers +@cindex buffer + + 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 which are not visiting files. While several buffers may +exist at one time, exactly 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? +* 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. +* Modification Time:: Determining whether the visited file was changed + ``behind Emacs's back''. +* Read Only Buffers:: Modifying text is not allowed in a read-only buffer. +* The Buffer List:: How to look at all the existing buffers. +* Creating Buffers:: Functions that create buffers. +* Killing Buffers:: Buffers exist until explicitly killed. +* Current Buffer:: Designating a buffer as current + so primitives will access its contents. +@end menu + +@node Buffer Basics +@comment node-name, next, previous, up +@section Buffer Basics + +@ifinfo + 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 which are not visiting files. While several buffers may +exist at one time, exactly 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 + + Buffers in Emacs editing are objects which have distinct names and +hold text that can be edited. Buffers appear to Lisp programs as a +special data type. The contents of a buffer may be viewed as an +extendable string; 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 +variables, while other information is only accessible through +special-purpose functions. For example, the visited file name is +directly accessible through a variable, while the value of point is +accessible only through a primitive function. + + Buffer-specific information that is directly accessible is stored in +@dfn{buffer-local} variable bindings, which are variable values that are +effective only in a particular buffer. This feature allows each buffer +to override the values of certain variables. Most major modes override +variables such as @code{fill-column} or @code{comment-column} in this +way. For more information about buffer-local variables and functions +related to them, see @ref{Buffer-Local Variables}. + + For functions and variables related to visiting files in buffers, see +@ref{Visiting Files} and @ref{Saving Buffers}. For functions and +variables related to the display of buffers in windows, see +@ref{Buffers and Windows}. + +@defun bufferp object +This function returns @code{t} if @var{object} is a buffer, +@code{nil} otherwise. +@end defun + +@node Buffer Names +@section Buffer Names +@cindex buffer names + + Each buffer has a unique name, which is a string. Many of the +functions that work on buffers accept either a buffer or a buffer name +as an argument. Any argument called @var{buffer-or-name} is of this +sort, and an error is signaled if it is neither a string nor a buffer. +Any argument called @var{buffer} must be an actual buffer +object, not a name. + + Buffers that are ephemeral and generally uninteresting to the user +have names starting with a space, so that the @code{list-buffers} or +@code{buffer-menu} commands don't mention them. A name starting with +space also initially disables recording undo information; see +@ref{Undo}. + +@defun buffer-name &optional buffer +This function returns the name of @var{buffer} as a string. If +@var{buffer} is not supplied, it defaults to the current buffer. + +If @code{buffer-name} returns @code{nil}, it means that @var{buffer} +has been killed. @xref{Killing Buffers}. + +@example +@group +(buffer-name) + @result{} "buffers.texi" +@end group + +@group +(setq foo (get-buffer "temp")) + @result{} #<buffer temp> +@end group +@group +(kill-buffer foo) + @result{} nil +@end group +@group +(buffer-name foo) + @result{} nil +@end group +@group +foo + @result{} #<killed buffer> +@end group +@end example +@end defun + +@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}. + +@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*}. +@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: + +@example +@group +(setq b (get-buffer "lewis")) + @result{} #<buffer lewis> +@end group +@group +(get-buffer b) + @result{} #<buffer lewis> +@end group +@group +(get-buffer "Frazzle-nots") + @result{} nil +@end group +@end example + +See also the function @code{get-buffer-create} in @ref{Creating Buffers}. +@end defun + +@c Emacs 19 feature +@defun generate-new-buffer-name starting-name +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{}>}. + +See the related function @code{generate-new-buffer} in @ref{Creating +Buffers}. +@end defun + +@node Buffer File Name +@section Buffer File Name +@cindex visited file +@cindex buffer file name +@cindex file name of buffer + + The @dfn{buffer file name} is the name of the file that is visited in +that buffer. When a buffer is not visiting a file, its buffer file name +is @code{nil}. Most of the time, the buffer name is the same as the +nondirectory part of the buffer file name, but the buffer file name and +the buffer name are distinct and can be set independently. +@xref{Visiting Files}. + +@defun buffer-file-name &optional buffer +This function returns the absolute file name of the file that +@var{buffer} is visiting. If @var{buffer} is not visiting any file, +@code{buffer-file-name} returns @code{nil}. If @var{buffer} is not +supplied, it defaults to the current buffer. + +@example +@group +(buffer-file-name (other-buffer)) + @result{} "/usr/user/lewis/manual/files.texi" +@end group +@end example +@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}. + +@example +@group +buffer-file-name + @result{} "/usr/user/lewis/manual/buffers.texi" +@end 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. +@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}. +@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}. + +The value is normally a list of the form @code{(@var{filenum} +@var{devnum})}. This pair of numbers uniquely identifies the file among +all files accessible on the system. See the function +@code{file-attributes}, in @ref{File Attributes}, for more information +about them. +@end defvar + +@defun get-file-buffer filename +This function returns the buffer visiting file @var{filename}. If +there is no such buffer, it returns @code{nil}. The argument +@var{filename}, which must be a string, is expanded (@pxref{File Name +Expansion}), then compared against the visited file names of all live +buffers. + +@example +@group +(get-file-buffer "buffers.texi") + @result{} #<buffer buffers.texi> +@end group +@end example + +In unusual circumstances, there can be more than one buffer visiting +the same file name. In such cases, this function returns the first +such buffer in the buffer list. +@end defun + +@deffn Command set-visited-file-name filename +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 +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 +knows) match the contents of @var{filename}, even if it matched the +former visited file. + +If @var{filename} is @code{nil} or the empty string, that stands for +``no visited file''. In this case, @code{set-visited-file-name} marks +the buffer as having no visited file. + +@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. +@end defvar + +@node Buffer Modification +@section Buffer Modification +@cindex buffer modification +@cindex modification flag (of buffer) + + Emacs keeps a flag called the @dfn{modified flag} for each buffer, to +record whether you have changed the text of the buffer. This flag is +set to @code{t} whenever you alter the contents of the buffer, and +cleared to @code{nil} when you save it. Thus, the flag shows whether +there are unsaved changes. The flag value is normally shown in the mode +line (@pxref{Mode Line Variables}), and controls saving (@pxref{Saving +Buffers}) and auto-saving (@pxref{Auto-Saving}). + + Some Lisp programs set the flag explicitly. For example, the function +@code{set-visited-file-name} sets the flag to @code{t}, because the text +does not match the newly-visited file, even if it is unchanged from the +file formerly visited. + + The functions that modify the contents of buffers are described in +@ref{Text}. + +@defun buffer-modified-p &optional buffer +This function returns @code{t} if the buffer @var{buffer} has been modified +since it was last read in from a file or saved, or @code{nil} +otherwise. If @var{buffer} is not supplied, the current buffer +is tested. +@end defun + +@defun set-buffer-modified-p flag +This function marks the current buffer as modified if @var{flag} is +non-@code{nil}, or as unmodified if the flag is @code{nil}. + +Another effect of calling this function is to cause unconditional +redisplay of the mode line for the current buffer. In fact, the +function @code{force-mode-line-update} works by doing this: + +@example +@group +(set-buffer-modified-p (buffer-modified-p)) +@end group +@end example +@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. +@end deffn + +@c Emacs 19 feature +@defun buffer-modified-tick &optional buffer +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 + +@node Modification Time +@comment node-name, next, previous, up +@section Comparison of Modification Time +@cindex comparison of modification time +@cindex modification time, comparison of + + Suppose that you visit a file and make changes in its buffer, and +meanwhile the file itself is changed on disk. At this point, saving the +buffer would overwrite the changes in the file. Occasionally this may +be what you want, but usually it would lose valuable information. Emacs +therefore checks the file's modification time using the functions +described below before saving the file. + +@defun verify-visited-file-modtime buffer +This function compares what @var{buffer} has recorded for the +modification time of its visited file against the actual modification +time of the file as recorded by the operating system. The two should be +the same unless some other process has written the file since Emacs +visited or saved it. + +The function returns @code{t} if the last actual modification time and +Emacs's recorded modification time are the same, @code{nil} otherwise. +@end defun + +@defun clear-visited-file-modtime +This function clears out the record of the last modification time of +the file being visited by the current buffer. As a result, the next +attempt to save this buffer will not complain of a discrepancy in +file modification times. + +This function is called in @code{set-visited-file-name} and other +exceptional places where the usual test to avoid overwriting a changed +file should not be done. +@end defun + +@c Emacs 19 feature +@defun visited-file-modtime +This function returns the buffer's recorded last file modification time, +as a list of the form @code{(@var{high} . @var{low})}. (This is the +same format that @code{file-attributes} uses to return time values; see +@ref{File Attributes}.) +@end defun + +@c Emacs 19 feature +@defun set-visited-file-modtime &optional time +This function updates the buffer's record of the last modification time +of the visited file, to the value specified by @var{time} if @var{time} +is not @code{nil}, and otherwise to the last modification time of the +visited file. + +If @var{time} is not @code{nil}, it should have the form +@code{(@var{high} . @var{low})} or @code{(@var{high} @var{low})}, in +either case containing two integers, each of which holds 16 bits of the +time. + +This function is useful if the buffer was not read from the file +normally, or if the file itself has been changed for some known benign +reason. +@end defun + +@defun ask-user-about-supersession-threat fn +@cindex obsolete buffer +This function is used to ask a user how to proceed after an attempt to +modify an obsolete buffer. An @dfn{obsolete buffer} is an unmodified +buffer for which the associated file on disk is newer than the last +save-time of the buffer. This means some other program has probably +altered the file. + +This function is called automatically by Emacs on the proper +occasions. It exists so you can customize Emacs by redefining it. +See the file @file{userlock.el} for the standard definition. + +@kindex file-supersession +Depending on the user's answer, the function may return normally, in +which case the modification of the buffer proceeds, or it may signal a +@code{file-supersession} error with data @code{(@var{fn})}, in which +case the proposed buffer modification is not allowed. + +See also the file locking mechanism in @ref{File Locks}. +@end defun + +@node Read Only Buffers +@section Read-Only Buffers +@cindex read-only buffer +@cindex buffer, read-only + + If a buffer is @dfn{read-only}, then you cannot change its contents, +although you may change your view of the contents by scrolling and +narrowing. + + Read-only buffers are used in two kinds of situations: + +@itemize @bullet +@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 +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-M-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. + +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. +@end itemize + +@defvar buffer-read-only +This buffer-local variable specifies whether the buffer is read-only. +The buffer is read-only if this variable is non-@code{nil}. +@end defvar + +@defvar inhibit-read-only +If this variable is non-@code{nil}, then read-only buffers and read-only +characters may be modified. The value of @code{buffer-read-only} does +not matter when @code{inhibit-read-only} is non-@code{nil}. + +If @code{inhibit-read-only} is @code{t}, all @code{read-only} text +properties have no effect (@pxref{Special Properties}). If +@code{inhibit-read-only} is a list, then @code{read-only} text +properties are ignored if they are members of the list (comparison is +done with @code{eq}). +@end defvar + +@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 +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}. +@end deffn + +@defun barf-if-buffer-read-only +This function signals a @code{buffer-read-only} error if the current +buffer is read-only. @xref{Interactive Call}, for another way to +signal an error if the current buffer is read-only. +@end defun + +@node The Buffer List +@section The Buffer List +@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 +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. + +@example +@group +(buffer-list) + @result{} (#<buffer buffers.texi> + #<buffer *Minibuf-1*> #<buffer buffer.c> + #<buffer *Help*> #<buffer TAGS>) +@end group + +@group +;; @r{Note that the name of the minibuffer} +;; @r{begins with a space!} +(mapcar (function buffer-name) (buffer-list)) + @result{} ("buffers.texi" " *Minibuf-1*" + "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 +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. + +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. + +@c Emacs 19 feature +If @var{visible-ok} is @code{nil}, @code{other-buffer} avoids returning +a buffer visible in any window on any visible frame, except as a last +resort. If @var{visible-ok} is non-@code{nil}, then it does not matter +whether a buffer is displayed somewhere or not. + +If no suitable buffer exists, the buffer @samp{*scratch*} is returned +(and created, if necessary). +@end defun + +@deffn Command bury-buffer &optional buffer-or-name +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. + +If @var{buffer-or-name} is @code{nil} or omitted, this means to bury +the current buffer. In addition, this switches to some other buffer +(obtained using @code{other-buffer}) in the selected window. If the +buffer is displayed in a window other than the selected one, it remains +there. + +If you wish to replace a buffer in all the windows that display it, use +@code{replace-buffer-in-windows}. @xref{Buffers and Windows}. +@end deffn + +@node Creating Buffers +@section Creating Buffers +@cindex creating buffers +@cindex buffers, creating + + This section describes the two primitives for creating buffers. +@code{get-buffer-create} creates a buffer if it finds no existing +buffer; @code{generate-new-buffer} always creates a new buffer, and +gives it a unique name. + + Other functions you can use to create buffers include +@code{with-output-to-temp-buffer} (@pxref{Temporary Displays}) and +@code{create-file-buffer} (@pxref{Visiting Files}). Starting a +subprocess can also create a buffer (@pxref{Processes}). + +@defun get-buffer-create name +This function returns a buffer named @var{name}. It returns an existing +buffer with that name, if one exists; otherwise, it creates a new +buffer. The buffer does not become the current buffer---this function +does not change which buffer is current. + +An error is signaled if @var{name} is not a string. + +@example +@group +(get-buffer-create "foo") + @result{} #<buffer foo> +@end group +@end example + +The major mode for the new buffer is set according to the variable +@code{default-major-mode}. @xref{Auto Major Mode}. +@end defun + +@defun generate-new-buffer name +This function returns a newly created, empty buffer, but does not make +it current. If there is no buffer named @var{name}, then that is the +name of the new buffer. If that name is in use, this function adds +suffixes of the form @samp{<@var{n}>} are added to @var{name}, where +@var{n} is an integer. It tries successive integers starting with 2 +until it finds an available name. + +An error is signaled if @var{name} is not a string. + +@example +@group +(generate-new-buffer "bar") + @result{} #<buffer bar> +@end group +@group +(generate-new-buffer "bar") + @result{} #<buffer bar<2>> +@end group +@group +(generate-new-buffer "bar") + @result{} #<buffer bar<3>> +@end group +@end example + +The major mode for the new buffer is set by the value of +@code{default-major-mode}. @xref{Auto Major Mode}. + +See the related function @code{generate-new-buffer-name} in @ref{Buffer +Names}. +@end defun + +@node Killing Buffers +@section Killing Buffers +@cindex killing buffers +@cindex buffers, killing + + @dfn{Killing a buffer} makes its name unknown to Emacs and makes its +space available for other use. + + The buffer object for the buffer which 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}. + + If you kill a buffer that is current or displayed in a window, Emacs +automatically selects or displays some other buffer instead. This means +that killing a buffer can in general change the current buffer. +Therefore, when you kill a buffer, you should also take the precautions +associated with changing the current buffer (unless you happen to know +that the buffer being killed isn't current). @xref{Current Buffer}. + + The @code{buffer-name} of a killed buffer is @code{nil}. You can use +this feature to test whether a buffer has been killed: + +@example +@group +(defun buffer-killed-p (buffer) + "Return t if BUFFER is killed." + (not (buffer-name buffer))) +@end group +@end example + +@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}. + +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}. + +If the buffer is visiting a file and contains unsaved changes, +@code{kill-buffer} asks the user to confirm before the buffer is killed. +It does this even if not called interactively. To prevent the request +for confirmation, clear the modified flag before calling +@code{kill-buffer}. @xref{Buffer Modification}. + +@vindex kill-buffer-query-functions +You can program additional requests for confirmation. 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 +non-@code{nil}, the buffer is not killed. + +@c Emacs 19 feature +@vindex kill-buffer-hook +Just before actually killing the buffer, after asking all questions, +@code{kill-buffer} runs the normal hook @code{kill-buffer-hook}. The +buffer to be killed is current when the hook functions run. +@xref{Hooks}. + +Killing a buffer that is already dead has no effect. + +@smallexample +(kill-buffer "foo.unchanged") + @result{} nil +(kill-buffer "foo.changed") + +---------- Buffer: Minibuffer ---------- +Buffer foo.changed modified; kill anyway? (yes or no) @kbd{yes} +---------- Buffer: Minibuffer ---------- + + @result{} nil +@end smallexample +@end deffn + +@node Current Buffer +@section The Current Buffer +@cindex selecting a buffer +@cindex changing to another buffer +@cindex current buffer + + There are, in general, many buffers in an Emacs session. At any time, +one of them is designated as the @dfn{current buffer}. This is the +buffer in which most editing takes place, because most of the primitives +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. + + 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 +is designated. + + When an editing command returns to the editor command loop, the +command loop designates the buffer displayed in the selected window as +current, to prevent confusion: the buffer that the cursor is in, when +Emacs reads a command, is the one to which the command will apply. +(@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}. + + However, 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 +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): + +@example +@group +(defun append-to-buffer (buffer start end) + "Append to specified buffer the text of the region. +@dots{}" + (interactive "BAppend to buffer: \nr") + (let ((oldbuf (current-buffer))) + (save-excursion + (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. + + If the buffer appended to happens to be displayed in some window, +the next redisplay will show how its text has changed. Otherwise, you +will not see the change immediately on the screen. The buffer becomes +current temporarily during the execution of the command, but this does +not cause it to be displayed. + + If you make local bindings (with @code{let} or function arguments) for +a variable that may also have buffer-local bindings, make sure that the +same buffer is current at the beginning and at the end of the local +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. + + 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 not to do: + +@example +@group +(let (buffer-read-only + (obuf (current-buffer))) + (set-buffer @dots{}) + @dots{} + (set-buffer obuf)) +@end group +@end example + +@noindent +Using @code{save-excursion}, as shown below, handles quitting, errors +and @code{throw} as well as ordinary evaluation. + +@example +@group +(let (buffer-read-only) + (save-excursion + (set-buffer @dots{}) + @dots{})) +@end group +@end example + +@defun current-buffer +This function returns the current buffer. + +@example +@group +(current-buffer) + @result{} #<buffer buffers.texi> +@end group +@end example +@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 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 diff --git a/lispref/windows.texi b/lispref/windows.texi new file mode 100644 index 00000000000..a859fd9cf20 --- /dev/null +++ b/lispref/windows.texi @@ -0,0 +1,1592 @@ +@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 See the file elisp.texi for copying conditions. +@setfilename ../info/windows +@node Windows, Frames, Buffers, Top +@chapter Windows + + This chapter describes most of the functions and variables related to +Emacs windows. See @ref{Display}, for information on how text is +displayed in windows. + +@menu +* Basic Windows:: Basic information on using windows. +* Splitting Windows:: Splitting one window into two windows. +* Deleting Windows:: Deleting a window gives its space to other windows. +* Selecting Windows:: The selected window is the one that you edit in. +* Cyclic Window Ordering:: Moving around the existing windows. +* Buffers and Windows:: Each window displays the contents of a buffer. +* Displaying Buffers:: Higher-lever functions for displaying a buffer + and choosing a window for it. +* Choosing Window:: How to choose a window for displaying a buffer. +* Window Point:: Each window has its own location of point. +* Window Start:: The display-start position controls which text + is on-screen in the window. +* Vertical Scrolling:: Moving text up and down in the window. +* Horizontal Scrolling:: Moving text sideways on the window. +* Size of Window:: Accessing the size of a window. +* Resizing Windows:: Changing the size of a window. +* Coordinates and Windows::Converting coordinates to windows. +* Window Configurations:: Saving and restoring the state of the screen. +@end menu + +@node Basic Windows +@section Basic Concepts of Emacs Windows +@cindex window +@cindex selected window + + A @dfn{window} is the physical area of the screen in which a buffer is +displayed. The term is also used to refer to a Lisp object which +represents that screen area in Emacs Lisp. It should be +clear from the context which is meant. + + There is always at least one window in any frame. In each frame, at +any time, one and only one window is designated as @dfn{selected within +the frame}. The frame's cursor appears in that window. There is also +one selected frame; and the window selected within that frame is +@dfn{the selected window}. The selected window's buffer is usually the +current buffer (except when @code{set-buffer} has been used). +@xref{Current Buffer}. + + For all intents, a window only exists while it is displayed on the +terminal. Once removed from the display, the window is effectively +deleted and should not be used, @emph{even though there may still be +references to it} from other Lisp objects. Restoring a saved window +configuration is the only way for a window no longer on the screen to +come back to life. (@xref{Deleting Windows}.) + + Each window has the following attributes: + +@itemize @bullet +@item +containing frame + +@item +window height + +@item +window width + +@item +window edges with respect to the screen or frame + +@item +the buffer it displays + +@item +position within the buffer at the upper left of the window + +@item +the amount of horizontal scrolling, in columns + +@item +point + +@item +the mark + +@item +how recently the window was selected +@end itemize + +@cindex multiple windows + Users create multiple windows so they can look at several buffers at +once. Lisp libraries use multiple windows for a variety of reasons, but +most often to give different views of the same information. In Rmail, +for example, you can move through a summary buffer in one window while +the other window shows messages one at a time as they are reached. + + The meaning of ``window'' in Emacs is similar to what it means in the +context of general purpose window systems such as X, but not identical. +The X Window System subdivides the screen into X windows; Emacs uses one +or more X windows, called @dfn{frames} in Emacs terminology, and +subdivides each of them into (nonoverlapping) Emacs windows. When you +use Emacs on an ordinary display terminal, Emacs subdivides the terminal +screen into Emacs windows. + +@cindex terminal screen +@cindex screen of terminal +@cindex tiled windows + Most window systems support arbitrarily located overlapping windows. +In contrast, Emacs windows are @dfn{tiled}; they never overlap, and +together they fill the whole of the screen or frame. Because of the way +in which Emacs creates new windows and resizes them, you can't create +every conceivable tiling of windows on an Emacs frame. @xref{Splitting +Windows}, and @ref{Size of Window}. + + @xref{Display}, for information on how the contents of the +window's buffer are displayed in the window. + +@defun windowp object + This function returns @code{t} if @var{object} is a window. +@end defun + +@node Splitting Windows +@section Splitting Windows +@cindex splitting windows +@cindex window splitting + + The functions described here are the primitives used to split a window +into two windows. Two higher level functions sometimes split a window, +but not always: @code{pop-to-buffer} and @code{display-buffer} +(@pxref{Displaying Buffers}). + + The functions described here do not accept a buffer as an argument. +The two ``halves'' of the split window initially display the same buffer +previously visible in the window that was split. + +@deffn Command split-window &optional window size horizontal +This function splits @var{window} into two windows. The original +window @var{window} remains the selected window, but occupies only +part of its former screen area. The rest is occupied by a newly created +window which is returned as the value of this function. + + If @var{horizontal} is non-@code{nil}, then @var{window} splits into +two side by side windows. The original window @var{window} keeps the +leftmost @var{size} columns, and gives the rest of the columns to the +new window. Otherwise, it splits into windows one above the other, and +@var{window} keeps the upper @var{size} lines and gives the rest of the +lines to the new window. The original window is therefore the +right-hand or upper of the two, and the new window is the left-hand or +lower. + + If @var{window} is omitted or @code{nil}, then the selected window is +split. If @var{size} is omitted or @code{nil}, then @var{window} is +divided evenly into two parts. (If there is an odd line, it is +allocated to the new window.) When @code{split-window} is called +interactively, all its arguments are @code{nil}. + + The following example starts with one window on a screen that is 50 +lines high by 80 columns wide; then the window is split. + +@smallexample +@group +(setq w (selected-window)) + @result{} #<window 8 on windows.texi> +(window-edges) ; @r{Edges in order:} + @result{} (0 0 80 50) ; @r{left--top--right--bottom} +@end group + +@group +;; @r{Returns window created} +(setq w2 (split-window w 15)) + @result{} #<window 28 on windows.texi> +@end group +@group +(window-edges w2) + @result{} (0 15 80 50) ; @r{Bottom window;} + ; @r{top is line 15} +@end group +@group +(window-edges w) + @result{} (0 0 80 15) ; @r{Top window} +@end group +@end smallexample + +The screen looks like this: + +@smallexample +@group + __________ + | | line 0 + | w | + |__________| + | | line 15 + | w2 | + |__________| + line 50 + column 0 column 80 +@end group +@end smallexample + +Next, the top window is split horizontally: + +@smallexample +@group +(setq w3 (split-window w 35 t)) + @result{} #<window 32 on windows.texi> +@end group +@group +(window-edges w3) + @result{} (35 0 80 15) ; @r{Left edge at column 35} +@end group +@group +(window-edges w) + @result{} (0 0 35 15) ; @r{Right edge at column 35} +@end group +@group +(window-edges w2) + @result{} (0 15 80 50) ; @r{Bottom window unchanged} +@end group +@end smallexample + +Now, the screen looks like this: + +@smallexample +@group + column 35 + __________ + | | | line 0 + | w | w3 | + |___|______| + | | line 15 + | w2 | + |__________| + line 50 + column 0 column 80 +@end group +@end smallexample +@end deffn + +@deffn Command split-window-vertically size +This function splits the selected window into two windows, one above +the other, leaving the selected window with @var{size} lines. + +This function is simply an interface to @code{split-windows}. +Here is the complete function definition for it: + +@smallexample +@group +(defun split-window-vertically (&optional arg) + "Split current window into two windows, one above the other." + (interactive "P") + (split-window nil (and arg (prefix-numeric-value arg)))) +@end group +@end smallexample +@end deffn + +@deffn Command split-window-horizontally size +This function splits the selected window into two windows +side-by-side, leaving the selected window with @var{size} columns. + +This function is simply an interface to @code{split-windows}. Here is +the complete definition for @code{split-window-horizontally} (except for +part of the documentation string): + +@smallexample +@group +(defun split-window-horizontally (&optional arg) + "Split selected window into two windows, side by side..." + (interactive "P") + (split-window nil (and arg (prefix-numeric-value arg)) t)) +@end group +@end smallexample +@end deffn + +@defun one-window-p &optional no-mini all-frames +This function returns non-@code{nil} if there is only one window. The +argument @var{no-mini}, if non-@code{nil}, means don't count the +minibuffer even if it is active; otherwise, the minibuffer window is +included, if active, in the total number of windows which is compared +against one. + +The argument @var{all-frames} specifies which frames to consider. Here +are the possible values and their meanings: + +@table @asis +@item @code{nil} +Count the windows in the selected frame, plus the minibuffer used +by that frame even if it lies in some other frame. + +@item @code{t} +Count all windows in all existing frames. + +@item @code{visible} +Count all windows in all visible frames. + +@item anything else +Count precisely the windows in the selected frame, and no others. +@end table +@end defun + +@node Deleting Windows +@section Deleting Windows +@cindex deleting windows + +A window remains visible on its frame unless you @dfn{delete} it by +calling certain functions that delete windows. A deleted window cannot +appear on the screen, but continues to exist as a Lisp object until +there are no references to it. There is no way to cancel the deletion +of a window aside from restoring a saved window configuration +(@pxref{Window Configurations}). Restoring a window configuration also +deletes any windows that aren't part of that configuration. + + When you delete a window, the space it took up is given to one +adjacent sibling. (In Emacs version 18, the space was divided evenly +among all the siblings.) + +@c Emacs 19 feature +@defun window-live-p window +This function returns @code{nil} if @var{window} is deleted, and +@code{t} otherwise. + +@strong{Warning:} erroneous information or fatal errors may result from +using a deleted window as if it were live. +@end defun + +@deffn Command delete-window &optional window +This function removes @var{window} from the display. If @var{window} +is omitted, then the selected window is deleted. An error is signaled +if there is only one window when @code{delete-window} is called. + +This function returns @code{nil}. + +When @code{delete-window} is called interactively, @var{window} +defaults to the selected window. +@end deffn + +@deffn Command delete-other-windows &optional window +This function makes @var{window} the only window on its frame, by +deleting the other windows in that frame. If @var{window} is omitted or +@code{nil}, then the selected window is used by default. + +The result is @code{nil}. +@end deffn + +@deffn Command delete-windows-on buffer &optional frame +This function deletes all windows showing @var{buffer}. If there are +no windows showing @var{buffer}, it does nothing. + +@code{delete-windows-on} operates frame by frame. If a frame has +several windows showing different buffers, then those showing +@var{buffer} are removed, and the others expand to fill the space. If +all windows in some frame are showing @var{buffer} (including the case +where there is only one window), then the frame reverts to having a +single window showing another buffer chosen with @code{other-buffer}. +@xref{The Buffer List}. + +The argument @var{frame} controls which frames to operate on: + +@itemize @bullet +@item +If it is @code{nil}, operate on the selected frame. +@item +If it is @code{t}, operate on all frames. +@item +If it is @code{visible}, operate on all visible frames. +@item +If it is a frame, operate on that frame. +@end itemize + +This function always returns @code{nil}. +@end deffn + +@node Selecting Windows +@section Selecting Windows +@cindex selecting windows + + When a window is selected, the buffer in the window becomes the current +buffer, and the cursor will appear in it. + +@defun selected-window +This function returns the selected window. This is the window in +which the cursor appears and to which many commands apply. +@end defun + +@defun select-window window +This function makes @var{window} the selected window. The cursor then +appears in @var{window} (on redisplay). The buffer being displayed in +@var{window} is immediately designated the current buffer. + +The return value is @var{window}. + +@example +@group +(setq w (next-window)) +(select-window w) + @result{} #<window 65 on windows.texi> +@end group +@end example +@end defun + +@cindex finding windows + The following functions choose one of the windows on the screen, +offering various criteria for the choice. + +@defun get-lru-window &optional frame +This function returns the window least recently ``used'' (that is, +selected). The selected window is always the most recently used window. + +The selected window can be the least recently used window if it is the +only window. A newly created window becomes the least recently used +window until it is selected. A minibuffer window is never a candidate. + +The argument @var{frame} controls which set of windows are +considered. + +@itemize @bullet +@item +If it is @code{nil}, consider windows on the selected frame. +@item +If it is @code{t}, consider windows on all frames. +@item +If it is @code{visible}, consider windows on all visible frames. +@item +If it is a frame, consider windows on that frame. +@end itemize +@end defun + +@defun get-largest-window &optional frame +This function returns the window with the largest area (height times +width). If there are no side-by-side windows, then this is the window +with the most lines. A minibuffer window is never a candidate. + +If there are two windows of the same size, then the function returns +the window which is first in the cyclic ordering of windows (see +following section), starting from the selected window. + +The argument @var{frame} controls which set of windows are +considered. See @code{get-lru-window}, above. +@end defun + +@node Cyclic Window Ordering +@comment node-name, next, previous, up +@section Cyclic Ordering of Windows +@cindex cyclic ordering of windows +@cindex ordering of windows, cyclic +@cindex window ordering, cyclic + + When you use the command @kbd{C-x o} (@code{other-window}) to select +the next window, it moves through all the windows on the screen in a +specific cyclic order. For any given configuration of windows, this +order never varies. It is called the @dfn{cyclic ordering of windows}. + + This ordering generally goes from top to bottom, and from left to +right. But it may go down first or go right first, depending on the +order in which the windows were split. + + If the first split was vertical (into windows one above each other), +and then the subwindows were split horizontally, then the ordering is +left to right in the top of the frame, and then left to right in the +next lower part of the frame, and so on. If the first split was +horizontal, the ordering is top to bottom in the left part, and so on. +In general, within each set of siblings at any level in the window tree, +the order is left to right, or top to bottom. + +@defun next-window &optional window minibuf all-frames +@cindex minibuffer window +This function returns the window following @var{window} in the cyclic +ordering of windows. This is the window which @kbd{C-x o} would select +if done when @var{window} is selected. If @var{window} is the only +window visible, then this function returns @var{window}. If omitted, +@var{window} defaults to the selected window. + +The value of the argument @var{minibuf} determines whether the +minibuffer is included in the window order. Normally, when +@var{minibuf} is @code{nil}, the minibuffer is included if it is +currently active; this is the behavior of @kbd{C-x o}. (The minibuffer +window is active while the minibuffer is in use. @xref{Minibuffers}.) + +If @var{minibuf} is @code{t}, then the cyclic ordering includes the +minibuffer window even if it is not active. + +If @var{minibuf} is neither @code{t} nor @code{nil}, then the minibuffer +window is not included even if it is active. + +The argument @var{all-frames} specifies which frames to consider. Here +are the possible values and their meanings: + +@table @asis +@item @code{nil} +Consider all the windows in @var{window}'s frame, plus the minibuffer +used by that frame even if it lies in some other frame. + +@item @code{t} +Consider all windows in all existing frames. + +@item @code{visible} +Consider all windows in all visible frames. (To get useful results, you +must ensure @var{window} is in a visible frame.) + +@item anything else +Consider precisely the windows in @var{window}'s frame, and no others. +@end table + +This example assumes there are two windows, both displaying the +buffer @samp{windows.texi}: + +@example +@group +(selected-window) + @result{} #<window 56 on windows.texi> +@end group +@group +(next-window (selected-window)) + @result{} #<window 52 on windows.texi> +@end group +@group +(next-window (next-window (selected-window))) + @result{} #<window 56 on windows.texi> +@end group +@end example +@end defun + +@defun previous-window &optional window minibuf all-frames +This function returns the window preceding @var{window} in the cyclic +ordering of windows. The other arguments specify which windows to +include in the cycle, as in @code{next-window}. +@end defun + +@deffn Command other-window count +This function selects the @var{count}th following window in the cyclic +order. If count is negative, then it selects the @minus{}@var{count}th +preceding window. It returns @code{nil}. + +In an interactive call, @var{count} is the numeric prefix argument. +@end deffn + +@c Emacs 19 feature +@defun walk-windows proc &optional minibuf all-frames +This function cycles through all windows, calling @code{proc} +once for each window with the window as its sole argument. + +The optional arguments @var{minibuf} and @var{all-frames} specify the +set of windows to include in the scan. See @code{next-window}, above, +for details. +@end defun + +@node Buffers and Windows +@section Buffers and Windows +@cindex examining windows +@cindex windows, controlling precisely +@cindex buffers, controlled in windows + + This section describes low-level functions to examine windows or to +display buffers in windows in a precisely controlled fashion. +@iftex +See the following section for +@end iftex +@ifinfo +@xref{Displaying Buffers}, for +@end ifinfo +related functions that find a window to use and specify a buffer for it. +The functions described there are easier to use than these, but they +employ heuristics in choosing or creating a window; use these functions +when you need complete control. + +@defun set-window-buffer window buffer-or-name +This function makes @var{window} display @var{buffer-or-name} as its +contents. It returns @code{nil}. + +@example +@group +(set-window-buffer (selected-window) "foo") + @result{} nil +@end group +@end example +@end defun + +@defun window-buffer &optional window +This function returns the buffer that @var{window} is displaying. If +@var{window} is omitted, this function returns the buffer for the +selected window. + +@example +@group +(window-buffer) + @result{} #<buffer windows.texi> +@end group +@end example +@end defun + +@defun get-buffer-window buffer-or-name &optional all-frames +This function returns a window currently displaying +@var{buffer-or-name}, or @code{nil} if there is none. If there are +several such windows, then the function returns the first one in the +cyclic ordering of windows, starting from the selected window. +@xref{Cyclic Window Ordering}. + +The argument @var{all-frames} controls which windows to consider. + +@itemize @bullet +@item +If it is @code{nil}, consider windows on the selected frame. +@item +If it is @code{t}, consider windows on all frames. +@item +If it is @code{visible}, consider windows on all visible frames. +@item +If it is a frame, consider windows on that frame. +@end itemize +@end defun + +@deffn Command replace-buffer-in-windows buffer +This function replaces @var{buffer} with some other buffer in all +windows displaying it. The other buffer used is chosen with +@code{other-buffer}. In the usual applications of this function, you +don't care which other buffer is used; you just want to make sure that +@var{buffer} is no longer displayed. + +This function returns @code{nil}. +@end deffn + +@node Displaying Buffers +@section Displaying Buffers in Windows +@cindex switching to a buffer +@cindex displaying a buffer + + In this section we describe convenient functions that choose a window +automatically and use it to display a specified buffer. These functions +can also split an existing window in certain circumstances. We also +describe variables that parameterize the heuristics used for choosing a +window. +@iftex +See the preceding section for +@end iftex +@ifinfo +@xref{Buffers and Windows}, for +@end ifinfo +low-level functions that give you more precise control. + + Do not use the functions in this section in order to make a buffer +current so that a Lisp program can access or modify it; they are too +drastic for that purpose, since they change the display of buffers in +windows, which is gratuitous and will surprise the user. Instead, use +@code{set-buffer} (@pxref{Current Buffer}) and @code{save-excursion} +(@pxref{Excursions}), which designate buffers as current for programmed +access without affecting the display of buffers in windows. + +@deffn Command switch-to-buffer buffer-or-name &optional norecord +This function makes @var{buffer-or-name} the current buffer, and also +displays the buffer in the selected window. This means that a human can +see the buffer and subsequent keyboard commands will apply to it. +Contrast this with @code{set-buffer}, which makes @var{buffer-or-name} +the current buffer but does not display it in the selected window. +@xref{Current Buffer}. + +If @var{buffer-or-name} does not identify an existing buffer, then +a new buffer by that name is created. + +Normally the specified buffer is put at the front of the buffer list. +This affects the operation of @code{other-buffer}. However, if +@var{norecord} is non-@code{nil}, this is not done. @xref{The Buffer +List}. + +The @code{switch-to-buffer} function is often used interactively, as +the binding of @kbd{C-x b}. It is also used frequently in programs. It +always returns @code{nil}. +@end deffn + +@deffn Command switch-to-buffer-other-window buffer-or-name +This function makes @var{buffer-or-name} the current buffer and +displays it in a window not currently selected. It then selects that +window. The handling of the buffer is the same as in +@code{switch-to-buffer}. + +The previously selected window is absolutely never used to display the +buffer. If it is the only window, then it is split to make a distinct +window for this purpose. If the selected window is already displaying +the buffer, then it continues to do so, but another window is +nonetheless found to display it in as well. +@end deffn + +@defun pop-to-buffer buffer-or-name &optional other-window +This function makes @var{buffer-or-name} the current buffer and +switches to it in some window, preferably not the window previously +selected. The ``popped-to'' window becomes the selected window within +its frame. + +If the variable @code{pop-up-frames} is non-@code{nil}, +@code{pop-to-buffer} looks for a window in any visible frame already +displaying the buffer; if there is one, it returns that window and makes +it be selected within its frame. If there is none, it creates a new +frame and displays the buffer in it. + +If @code{pop-up-frames} is @code{nil}, then @code{pop-to-buffer} +operates entirely within the selected frame. (If the selected frame has +just a minibuffer, @code{pop-to-buffer} operates within the most +recently selected frame that was not just a minibuffer.) + +If the variable @code{pop-up-windows} is non-@code{nil}, windows may +be split to create a new window that is different from the original +window. For details, see @ref{Choosing Window}. + +If @var{other-window} is non-@code{nil}, @code{pop-to-buffer} finds or +creates another window even if @var{buffer-or-name} is already visible +in the selected window. Thus @var{buffer-or-name} could end up +displayed in two windows. On the other hand, if @var{buffer-or-name} is +already displayed in the selected window and @var{other-window} is +@code{nil}, then the selected window is considered sufficient display +for @var{buffer-or-name}, so that nothing needs to be done. + +If @var{buffer-or-name} is a string that does not name an existing +buffer, a buffer by that name is created. + +An example use of this function is found at the end of @ref{Filter +Functions}. +@end defun + +@node Choosing Window +@section Choosing a Window for Display + + This section describes the basic facility which chooses a window to +display a buffer in---@code{display-buffer}. All the higher-level +functions and commands use this subroutine. Here we describe how to use +@code{display-buffer} and how to customize it. + +@deffn Command display-buffer buffer-or-name &optional not-this-window +This command makes @var{buffer-or-name} appear in some window, like +@code{pop-to-buffer}, but it does not select that window and does not +make the buffer current. The identity of the selected window is +unaltered by this function. + +If @var{not-this-window} is non-@code{nil}, it means to display the +specified buffer in a window other than the selected one, even if it is +already on display in the selected window. This can cause the buffer to +appear in two windows at once. Otherwise, if @var{buffer-or-name} is +already being displayed in any window, that is good enough, so this +function does nothing. + +@code{display-buffer} returns the window chosen to display +@var{buffer-or-name}. + +Precisely how @code{display-buffer} finds or creates a window depends on +the variables described below. +@end deffn + +@defopt pop-up-windows +This variable controls whether @code{display-buffer} makes new windows. +If it is non-@code{nil} and there is only one window, then that window +is split. If it is @code{nil}, then @code{display-buffer} does not +split the single window, but uses it whole. +@end defopt + +@defopt split-height-threshold +This variable determines when @code{display-buffer} may split a window, +if there are multiple windows. @code{display-buffer} always splits the +largest window if it has at least this many lines. If the largest +window is not this tall, it is split only if it is the sole window and +@code{pop-up-windows} is non-@code{nil}. +@end defopt + +@c Emacs 19 feature +@defopt pop-up-frames +This variable controls whether @code{display-buffer} makes new frames. +If it is non-@code{nil}, @code{display-buffer} looks for an existing +window already displaying the desired buffer, on any visible frame. If +it finds one, it returns that window. Otherwise it makes a new frame. +The variables @code{pop-up-windows} and @code{split-height-threshold} do +not matter if @code{pop-up-frames} is non-@code{nil}. + +If @code{pop-up-frames} is @code{nil}, then @code{display-buffer} either +splits a window or reuses one. + +@xref{Frames}, for more information. +@end defopt + +@c Emacs 19 feature +@defvar pop-up-frame-function +This variable specifies how to make a new frame if @code{pop-up-frames} +is non-@code{nil}. + +Its value should be a function of no arguments. When +@code{display-buffer} makes a new frame, it does so by calling that +function, which should return a frame. The default value of the +variable is a function which creates a frame using parameters from +@code{pop-up-frame-alist}. +@end defvar + +@defvar pop-up-frame-alist +This variable holds an alist specifying frame parameters used when +@code{display-buffer} makes a new frame. @xref{Frame Parameters}, for +more information about frame parameters. +@end defvar + +@c Emacs 19 feature +@defvar display-buffer-function +This variable is the most flexible way to customize the behavior of +@code{display-buffer}. If it is non-@code{nil}, it should be a function +that @code{display-buffer} calls to do the work. The function should +accept two arguments, the same two arguments that @code{display-buffer} +received. It should choose or create a window, display the specified +buffer, and then return the window. + +This hook takes precedence over all the other options and hooks +described above. +@end defvar + +@c Emacs 19 feature +@cindex dedicated window +A window can be marked as ``dedicated'' to its buffer. Then +@code{display-buffer} does not try to use that window. + +@defun window-dedicated-p window +This function returns @code{t} if @var{window} is marked as dedicated; +otherwise @code{nil}. +@end defun + +@defun set-window-dedicated-p window flag +This function marks @var{window} as dedicated if @var{flag} is +non-@code{nil}, and nondedicated otherwise. +@end defun + +@node Window Point +@section Windows and Point +@cindex window position +@cindex window point +@cindex position in window +@cindex point in window + + Each window has its own value of point, independent of the value of +point in other windows displaying the same buffer. This makes it useful +to have multiple windows showing one buffer. + +@itemize @bullet +@item +The window point is established when a window is first created; it is +initialized from the buffer's point, or from the window point of another +window opened on the buffer if such a window exists. + +@item +Selecting a window sets the value of point in its buffer to the window's +value of point. Conversely, deselecting a window sets the window's +value of point from that of the buffer. Thus, when you switch between +windows that display a given buffer, the point value for the selected +window is in effect in the buffer, while the point values for the other +windows are stored in those windows. + +@item +As long as the selected window displays the current buffer, the window's +point and the buffer's point always move together; they remain equal. + +@item +@xref{Positions}, for more details on buffer positions. +@end itemize + + As far as the user is concerned, point is where the cursor is, and +when the user switches to another buffer, the cursor jumps to the +position of point in that buffer. + +@defun window-point window +This function returns the current position of point in @var{window}. +For a nonselected window, this is the value point would have (in that +window's buffer) if that window were selected. + +When @var{window} is the selected window and its buffer is also the +current buffer, the value returned is the same as point in that buffer. + +Strictly speaking, it would be more correct to return the +``top-level'' value of point, outside of any @code{save-excursion} +forms. But that value is hard to find. +@end defun + +@defun set-window-point window position +This function positions point in @var{window} at position +@var{position} in @var{window}'s buffer. +@end defun + +@node Window Start +@section The Window Start Position + + Each window contains a marker used to keep track of a buffer position +which specifies where in the buffer display should start. This position +is called the @dfn{display-start} position of the window (or just the +@dfn{start}). The character after this position is the one that appears +at the upper left corner of the window. It is usually, but not +inevitably, at the beginning of a text line. + +@defun window-start &optional window +@cindex window top line +This function returns the display-start position of window +@var{window}. If @var{window} is @code{nil}, the selected window is +used. For example, + +@example +@group +(window-start) + @result{} 7058 +@end group +@end example + +When you create a window, or display a different buffer in it, the the +display-start position is set to a display-start position recently used +for the same buffer, or 1 if the buffer doesn't have any. + +For a realistic example, see the description of @code{count-lines} in +@ref{Text Lines}. +@end defun + +@defun window-end &optional window +This function returns the position of the end of the display in window +@var{window}. If @var{window} is @code{nil}, the selected window is +used. +@end defun + +@defun set-window-start window position &optional noforce +This function sets the display-start position of @var{window} to +@var{position} in @var{window}'s buffer. + +The display routines insist that the position of point be visible when a +buffer is displayed. Normally, they change the display-start position +(that is, scroll the window) whenever necessary to make point visible. +However, if you specify the start position with this function using +@code{nil} for @var{noforce}, it means you want display to start at +@var{position} even if that would put the location of point off the +screen. If this does place point off screen, the display routines move +point to the left margin on the middle line in the window. + +For example, if point @w{is 1} and you set the start of the window @w{to +2}, then point would be ``above'' the top of the window. The display +routines will automatically move point if it is still 1 when redisplay +occurs. Here is an example: + +@example +@group +;; @r{Here is what @samp{foo} looks like before executing} +;; @r{the @code{set-window-start} expression.} +@end group + +@group +---------- Buffer: foo ---------- +@point{}This is the contents of buffer foo. +2 +3 +4 +5 +6 +---------- Buffer: foo ---------- +@end group + +@group +(set-window-start + (selected-window) + (1+ (window-start))) +@result{} 2 +@end group + +@group +;; @r{Here is what @samp{foo} looks like after executing} +;; @r{the @code{set-window-start} expression.} +---------- Buffer: foo ---------- +his is the contents of buffer foo. +2 +3 +@point{}4 +5 +6 +---------- Buffer: foo ---------- +@end group +@end example + +If @var{noforce} is non-@code{nil}, and @var{position} would place point +off screen at the next redisplay, then redisplay computes a new window-start +position that works well with point, and thus @var{position} is not used. + +This function returns @var{position}. +@end defun + +@defun pos-visible-in-window-p &optional position window +This function returns @code{t} if @var{position} is within the range +of text currently visible on the screen in @var{window}. It returns +@code{nil} if @var{position} is scrolled vertically out of view. The +argument @var{position} defaults to the current position of point; +@var{window}, to the selected window. Here is an example: + +@example +@group +(or (pos-visible-in-window-p + (point) (selected-window)) + (recenter 0)) +@end group +@end example + +The @code{pos-visible-in-window-p} function considers only vertical +scrolling. If @var{position} is out of view only because @var{window} +has been scrolled horizontally, @code{pos-visible-in-window-p} returns +@code{t}. @xref{Horizontal Scrolling}. +@end defun + +@node Vertical Scrolling +@section Vertical Scrolling +@cindex vertical scrolling +@cindex scrolling vertically + + Vertical scrolling means moving the text up or down in a window. It +works by changing the value of the window's display-start location. It +may also change the value of @code{window-point} to keep it on the +screen. + + In the commands @code{scroll-up} and @code{scroll-down}, the directions +``up'' and ``down'' refer to the motion of the text in the buffer at which +you are looking through the window. Imagine that the text is +written on a long roll of paper and that the scrolling commands move the +paper up and down. Thus, if you are looking at text in the middle of a +buffer and repeatedly call @code{scroll-down}, you will eventually see +the beginning of the buffer. + + Some people have urged that the opposite convention be used: they +imagine that the window moves over text that remains in place. Then +``down'' commands would take you to the end of the buffer. This view is +more consistent with the actual relationship between windows and the +text in the buffer, but it is less like what the user sees. The +position of a window on the terminal does not move, and short scrolling +commands clearly move the text up or down on the screen. We have chosen +names that fit the user's point of view. + + The scrolling functions (aside from @code{scroll-other-window}) have +unpredictable results if the current buffer is different from the buffer +that is displayed in the selected window. @xref{Current Buffer}. + +@deffn Command scroll-up &optional count +This function scrolls the text in the selected window upward +@var{count} lines. If @var{count} is negative, scrolling is actually +downward. + +If @var{count} is @code{nil} (or omitted), then the length of scroll +is @code{next-screen-context-lines} lines less than the usable height of +the window (not counting its mode line). + +@code{scroll-up} returns @code{nil}. +@end deffn + +@deffn Command scroll-down &optional count +This function scrolls the text in the selected window downward +@var{count} lines. If @var{count} is negative, scrolling is actually +upward. + +If @var{count} is omitted or @code{nil}, then the length of the scroll +is @code{next-screen-context-lines} lines less than the usable height of +the window. + +@code{scroll-down} returns @code{nil}. +@end deffn + +@deffn Command scroll-other-window &optional count +This function scrolls the text in another window upward @var{count} +lines. Negative values of @var{count}, or @code{nil}, are handled +as in @code{scroll-up}. + +The window that is scrolled is normally the one following the selected +window in the cyclic ordering of windows---the window that +@code{next-window} would return. @xref{Cyclic Window Ordering}. + +You can specify a buffer to scroll with the variable +@code{other-window-scroll-buffer}. When the selected window is the +minibuffer, the next window is normally the one at the top left corner. +You can specify a different window to scroll with the variable +@code{minibuffer-scroll-window}. This variable has no effect when any +other window is selected. @xref{Minibuffer Misc}. + +When the minibuffer is active, it is the next window if the selected +window is the one at the bottom right corner. In this case, +@code{scroll-other-window} attempts to scroll the minibuffer. If the +minibuffer contains just one line, it has nowhere to scroll to, so the +line reappears after the echo area momentarily displays the message +``Beginning of buffer''. +@end deffn + +@c Emacs 19 feature +@defvar other-window-scroll-buffer +If this variable is non-@code{nil}, it tells @code{scroll-other-window} +which buffer to scroll. +@end defvar + +@defopt scroll-step +This variable controls how scrolling is done automatically when point +moves off the screen. If the value is zero, then redisplay scrolls the +text to center point vertically in the window. If the value is a +positive integer @var{n}, then redisplay brings point back on screen by +scrolling @var{n} lines in either direction, if possible; otherwise, it +centers point if possible. The default value is zero. +@end defopt + +@defopt next-screen-context-lines +The value of this variable is the number of lines of continuity to +retain when scrolling by full screens. For example, @code{scroll-up} +with an argument of @code{nil} scrolls so that this many lines at the +bottom of the window appear instead at the top. The default value is +@code{2}. +@end defopt + +@deffn Command recenter &optional count +@cindex centering point +This function scrolls the selected window to put the text where point +is located at a specified vertical position within the window. + +If @var{count} is a nonnegative number, it puts the line containing +point @var{count} lines down from the top of the window. If @var{count} +is a negative number, then it counts upward from the bottom of the +window, so that @minus{}1 stands for the last usable line in the window. +If @var{count} is a non-@code{nil} list, then it stands for the line in +the middle of the window. + +If @var{count} is @code{nil}, @code{recenter} puts the line containing +point in the middle of the window, then clears and redisplays the entire +selected frame. + +When @code{recenter} is called interactively, @var{count} is the raw +prefix argument. Thus, typing @kbd{C-u} as the prefix sets the +@var{count} to a non-@code{nil} list, while typing @kbd{C-u 4} sets +@var{count} to 4, which positions the current line four lines from the +top. + +Typing @kbd{C-u 0 C-l} positions the current line at the top of the +window. This action is so handy that some people bind the command to a +function key. For example, + +@example +@group +(defun line-to-top-of-window () + "Scroll current line to top of window. +Replaces three keystroke sequence C-u 0 C-l." + (interactive) + (recenter 0)) + +(global-set-key "\C-cl" 'line-to-top-of-window) +@end group +@end example +@end deffn + +@node Horizontal Scrolling +@section Horizontal Scrolling +@cindex horizontal scrolling + + Because we read English first from top to bottom and second from left +to right, horizontal scrolling is not like vertical scrolling. Vertical +scrolling involves selection of a contiguous portion of text to display. +Horizontal scrolling causes part of each line to go off screen. The +amount of horizontal scrolling is therefore specified as a number of +columns rather than as a position in the buffer. It has nothing to do +with the display-start position returned by @code{window-start}. + + Usually, no horizontal scrolling is in effect; then the leftmost +column is at the left edge of the window. In this state, scrolling to +the right is meaningless, since there is no data to the left of the +screen to be revealed by it; so this is not allowed. Scrolling to the +left is allowed; it scrolls the first columns of text off the edge of +the window and can reveal additional columns on the right that were +truncated before. Once a window has a nonzero amount of leftward +horizontal scrolling, you can scroll it back to the right, but only so +far as to reduce the net horizontal scroll to zero. There is no limit +to how far left you can scroll, but eventually all the text will +disappear off the left edge. + +@deffn Command scroll-left count +This function scrolls the selected window @var{count} columns to the +left (or to the right if @var{count} is negative). The return value is +the total amount of leftward horizontal scrolling in effect after the +change---just like the value returned by @code{window-hscroll}. +@end deffn + +@deffn Command scroll-right count +This function scrolls the selected window @var{count} columns to the +right (or to the left if @var{count} is negative). The return value is +the total amount of leftward horizontal scrolling in effect after the +change---just like the value returned by @code{window-hscroll}. + +Once you scroll a window as far right as it can go, back to its normal +position where the total leftward scrolling is zero, attempts to scroll +any farther right have no effect. +@end deffn + +@defun window-hscroll &optional window +This function returns the total leftward horizontal scrolling of +@var{window}---the number of columns by which the text in @var{window} +is scrolled left past the left margin. + +The value is never negative. It is zero when no horizontal scrolling +has been done in @var{window} (which is usually the case). + +If @var{window} is @code{nil}, the selected window is used. + +@example +@group +(window-hscroll) + @result{} 0 +@end group +@group +(scroll-left 5) + @result{} 5 +@end group +@group +(window-hscroll) + @result{} 5 +@end group +@end example +@end defun + +@defun set-window-hscroll window columns +This function sets the number of columns from the left margin that +@var{window} is scrolled to the value of @var{columns}. The argument +@var{columns} should be zero or positive; if not, it is taken as zero. + +The value returned is @var{columns}. + +@example +@group +(set-window-hscroll (selected-window) 10) + @result{} 10 +@end group +@end example +@end defun + + Here is how you can determine whether a given position @var{position} +is off the screen due to horizontal scrolling: + +@example +@group +(save-excursion + (goto-char @var{position}) + (and + (>= (- (current-column) (window-hscroll @var{window})) 0) + (< (- (current-column) (window-hscroll @var{window})) + (window-width @var{window})))) +@end group +@end example + +@node Size of Window +@section The Size of a Window +@cindex window size +@cindex size of window + + An Emacs window is rectangular, and its size information consists of +the height (the number of lines) and the width (the number of character +positions in each line). The mode line is included in the height. But +the width does not count the scroll bar or the column of @samp{|} +characters separates side-by-side windows. + + The following three functions return size information about a window: + +@defun window-height &optional window +This function returns the number of lines in @var{window}, including +its mode line. If @var{window} fills its entire frame, this is one less +than the value of @code{frame-height} on that frame (since the last line +is always reserved for the minibuffer). + +If @var{window} is @code{nil}, the function uses the selected window. + +@example +@group +(window-height) + @result{} 23 +@end group +@group +(split-window-vertically) + @result{} #<window 4 on windows.texi> +@end group +@group +(window-height) + @result{} 11 +@end group +@end example +@end defun + +@defun window-width &optional window +This function returns the number of columns in @var{window}. If +@var{window} fills its entire frame, this is the same as the value of +@code{frame-width} on that frame. The width does not include the +window's scroll bar or the column of @samp{|} characters that separates +side-by-side windows. + +If @var{window} is @code{nil}, the function uses the selected window. + +@example +@group +(window-width) + @result{} 80 +@end group +@end example +@end defun + +@defun window-edges &optional window +This function returns a list of the edge coordinates of @var{window}. +If @var{window} is @code{nil}, the selected window is used. + +The order of the list is @code{(@var{left} @var{top} @var{right} +@var{bottom})}, all elements relative to 0, 0 at the top left corner of +the frame. The element @var{right} of the value is one more than the +rightmost column used by @var{window}, and @var{bottom} is one more than +the bottommost row used by @var{window} and its mode-line. + +When you have side-by-side windows, the right edge value for a window +with a neighbor on the right includes the width of the separator between +the window and that neighbor. This separator may be a column of +@samp{|} characters or it may be a scroll bar. Since the width of the +window does not include this separator, the width does not equal the +difference between the right and left edges in this case. + +Here is the result obtained on a typical 24-line terminal with just one +window: + +@example +@group +(window-edges (selected-window)) + @result{} (0 0 80 23) +@end group +@end example + +If @var{window} is at the upper left corner of its frame, @var{right} +and @var{bottom} are the same as the values returned by +@code{(window-width)} and @code{(window-height)} respectively, and +@var{top} and @var{bottom} are zero. For example, the edges of the +following window are @w{@samp{0 0 5 8}}. Assuming that the frame has +more than 8 columns, the last column of the window (column 7) holds a +border rather than text. The last row (row 4) holds the mode line, +shown here with @samp{xxxxxxxxx}. + +@example +@group + 0 + _______ + 0 | | + | | + | | + | | + xxxxxxxxx 4 + + 7 +@end group +@end example + +When there are side-by-side windows, any window not at the right edge of +its frame has a separator in its last column or columns. The separator +counts as one or two columns in the width of the window. A window never +includes a separator on its left, since that belongs to the window to +the left. + +In the following example, let's suppose that the frame is 7 +columns wide. Then the edges of the left window are @w{@samp{0 0 4 3}} +and the edges of the right window are @w{@samp{4 0 7 3}}. + +@example +@group + ___ ___ + | | | + | | | + xxxxxxxxx + + 0 34 7 +@end group +@end example +@end defun + +@node Resizing Windows +@section Changing the Size of a Window +@cindex window resizing +@cindex changing window size +@cindex window size, changing + + The window size functions fall into two classes: high-level commands +that change the size of windows and low-level functions that access +window size. Emacs does not permit overlapping windows or gaps between +windows, so resizing one window affects other windows. + +@deffn Command enlarge-window size &optional horizontal +This function makes the selected window @var{size} lines bigger, +stealing lines from neighboring windows. It takes the lines from one +window at a time until that window is used up, then takes from another. +If a window from which lines are stolen shrinks below +@code{window-min-height} lines, that window disappears. + +If @var{horizontal} is non-@code{nil}, this function makes +@var{window} wider by @var{size} columns, stealing columns instead of +lines. If a window from which columns are stolen shrinks below +@code{window-min-width} columns, that window disappears. + +If the window's frame is smaller than @var{size} lines (or columns), +then the function makes the window occupy the entire height (or width) +of the frame. + +If @var{size} is negative, this function shrinks the window by +@minus{}@var{size} lines or columns. If that makes the window smaller +than the minimum size (@code{window-min-height} and +@code{window-min-width}), @code{enlarge-window} deletes the window. + +@code{enlarge-window} returns @code{nil}. +@end deffn + +@deffn Command enlarge-window-horizontally columns +This function makes the selected window @var{columns} wider. +It could be defined as follows: + +@example +@group +(defun enlarge-window-horizontally (columns) + (enlarge-window columns t)) +@end group +@end example +@end deffn + +@deffn Command shrink-window size &optional horizontal +This function is like @code{enlarge-window} but negates the argument +@var{size}, making the selected window smaller by giving lines (or +columns) to the other windows. If the window shrinks below +@code{window-min-height} or @code{window-min-width}, then it disappears. + +If @var{size} is negative, the window is enlarged by @minus{}@var{size} +lines or columns. +@end deffn + +@deffn Command shrink-window-horizontally columns +This function makes the selected window @var{columns} narrower. +It could be defined as follows: + +@example +@group +(defun shrink-window-horizontally (columns) + (shrink-window columns t)) +@end group +@end example +@end deffn + +@cindex minimum window size + The following two variables constrain the window size changing +functions to a minimum height and width. + +@defopt window-min-height +The value of this variable determines how short a window may become +before it is automatically deleted. Making a window smaller than +@code{window-min-height} automatically deletes it, and no window may be +created shorter than this. The absolute minimum height is two (allowing +one line for the mode line, and one line for the buffer display). +Actions which change window sizes reset this variable to two if it is +less than two. The default value is 4. +@end defopt + +@defopt window-min-width +The value of this variable determines how narrow a window may become +before it automatically deleted. Making a window smaller than +@code{window-min-width} automatically deletes it, and no window may be +created narrower than this. The absolute minimum width is one; any +value below that is ignored. The default value is 10. +@end defopt + +@node Coordinates and Windows +@section Coordinates and Windows + +This section describes how to compare screen coordinates with windows. + +@defun window-at x y &optional frame +This function returns the window containing the specified cursor +position in the frame @var{frame}. The coordinates @var{x} and @var{y} +are measured in characters and count from the top left corner of the +frame. If they are out of range, @code{window-at} returns @code{nil}. + +If you omit @var{frame}, the selected frame is used. +@end defun + +@defun coordinates-in-window-p coordinates window +This function checks whether a particular frame position falls within +the window @var{window}. + +The argument @var{coordinates} is a cons cell of this form: + +@example +(@var{x} . @var{y}) +@end example + +@noindent +The coordinates @var{x} and @var{y} are measured in characters, and +count from the top left corner of the screen or frame. + +The value of @code{coordinates-in-window-p} is non-@code{nil} if the +coordinates are inside @var{window}. The value also indicates what part +of the window the position is in, as follows: + +@table @code +@item (@var{relx} . @var{rely}) +The coordinates are inside @var{window}. The numbers @var{relx} and +@var{rely} are the equivalent window-relative coordinates for the +specified position, counting from 0 at the top left corner of the +window. + +@item mode-line +The coordinates are in the mode line of @var{window}. + +@item vertical-split +The coordinates are in the vertical line between @var{window} and its +neighbor to the right. This value occurs only if the window doesn't +have a scroll bar; positions in a scroll bar are considered outside the +window. + +@item nil +The coordinates are not in any part of @var{window}. +@end table + +The function @code{coordinates-in-window-p} does not require a frame as +argument because it always uses the frame that @var{window} is on. +@end defun + +@node Window Configurations +@section Window Configurations +@cindex window configurations +@cindex saving window information + + A @dfn{window configuration} records the entire layout of a +frame---all windows, their sizes, which buffers they contain, what part +of each buffer is displayed, and the values of point and the mark. You +can bring back an entire previous layout by restoring a window +configuration previously saved. + + If you want to record all frames instead of just one, use a frame +configuration instead of a window configuration. @xref{Frame +Configurations}. + +@defun current-window-configuration +This function returns a new object representing Emacs's current window +configuration, namely the number of windows, their sizes and current +buffers, which window is the selected window, and for each window the +displayed buffer, the display-start position, and the positions of point +and the mark. An exception is made for point in the current buffer, +whose value is not saved. +@end defun + +@defun set-window-configuration configuration +This function restores the configuration of Emacs's windows and +buffers to the state specified by @var{configuration}. The argument +@var{configuration} must be a value that was previously returned by +@code{current-window-configuration}. + +Here is a way of using this function to get the same effect +as @code{save-window-excursion}: + +@example +@group +(let ((config (current-window-configuration))) + (unwind-protect + (progn (split-window-vertically nil) + @dots{}) + (set-window-configuration config))) +@end group +@end example +@end defun + +@defspec save-window-excursion forms@dots{} +This special form records the window configuration, executes @var{forms} +in sequence, then restores the earlier window configuration. The window +configuration includes the value of point and the portion of the buffer +which is visible. It also includes the choice of selected window. +However, it does not include the value of point in the current buffer; +use @code{save-excursion} if you wish to preserve that. + +The return value is the value of the final form in @var{forms}. +For example: + +@example +@group +(split-window) + @result{} #<window 25 on control.texi> +@end group +@group +(setq w (selected-window)) + @result{} #<window 19 on control.texi> +@end group +@group +(save-window-excursion + (delete-other-windows w) + (switch-to-buffer "foo") + 'do-something) + @result{} do-something + ;; @r{The screen is now split again.} +@end group +@end example +@end defspec + +@defun window-configuration-p object +This function returns @code{t} if @var{object} is a window configuration. +@end defun + + Primitives to look inside of window configurations would make sense, +but none are implemented. It is not clear they are useful enough to be +worth implementing. |