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This is Info file ../../info/lispref.info, produced by Makeinfo-1.63 from the input file lispref.texi. Edition History: GNU Emacs Lisp Reference Manual Second Edition (v2.01), May 1993 GNU Emacs Lisp Reference Manual Further Revised (v2.02), August 1993 Lucid Emacs Lisp Reference Manual (for 19.10) First Edition, March 1994 XEmacs Lisp Programmer's Manual (for 19.12) Second Edition, April 1995 GNU Emacs Lisp Reference Manual v2.4, June 1995 XEmacs Lisp Programmer's Manual (for 19.13) Third Edition, July 1995 Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995 Free Software Foundation, Inc. Copyright (C) 1994, 1995 Sun Microsystems, Inc. Copyright (C) 1995 Amdahl Corporation. Copyright (C) 1995 Ben Wing. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that this permission notice may be stated in a translation approved by the Foundation. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided also that the section entitled "GNU General Public License" is included exactly as in the original, and provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that the section entitled "GNU General Public License" may be included in a translation approved by the Free Software Foundation instead of in the original English. File: lispref.info, Node: Current Buffer, Next: Buffer Names, Prev: Buffer Basics, Up: Buffers The Current Buffer ================== There are, in general, many buffers in an Emacs session. At any time, one of them is designated as the "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 (*note 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 `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 buffer that the command will apply to. (*Note Command Loop::.) Therefore, `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 *Note 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 `set-buffer' within a `save-excursion' that will restore the current buffer when your function is done (*note Excursions::.). Here is an example, the code for the command `append-to-buffer' (with the documentation string abridged): (defun append-to-buffer (buffer start end) "Append to specified buffer the text of the region. ..." (interactive "BAppend to buffer: \nr") (let ((oldbuf (current-buffer))) (save-excursion (set-buffer (get-buffer-create buffer)) (insert-buffer-substring oldbuf start end)))) This function binds a local variable to the current buffer, and then `save-excursion' records the values of point, the mark, and the original buffer. Next, `set-buffer' makes another buffer current. Finally, `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 `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 `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 `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: (let (buffer-read-only (obuf (current-buffer))) (set-buffer ...) ... (set-buffer obuf)) Using `save-excursion', as shown below, handles quitting, errors, and `throw', as well as ordinary evaluation. (let (buffer-read-only) (save-excursion (set-buffer ...) ...)) - Function: current-buffer This function returns the current buffer. (current-buffer) => #<buffer buffers.texi> - Function: set-buffer BUFFER-OR-NAME This function makes 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 BUFFER-OR-NAME. An error is signaled if BUFFER-OR-NAME does not identify an existing buffer. File: lispref.info, Node: Buffer Names, Next: Buffer File Name, Prev: Current Buffer, Up: Buffers 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 BUFFER-OR-NAME is of this sort, and an error is signaled if it is neither a string nor a buffer. Any argument called 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 `list-buffers' and `buffer-menu' commands don't mention them. A name starting with space also initially disables recording undo information; see *Note Undo::. - Function: buffer-name &optional BUFFER This function returns the name of BUFFER as a string. If BUFFER is not supplied, it defaults to the current buffer. If `buffer-name' returns `nil', it means that BUFFER has been killed. *Note Killing Buffers::. (buffer-name) => "buffers.texi" (setq foo (get-buffer "temp")) => #<buffer temp> (kill-buffer foo) => nil (buffer-name foo) => nil foo => #<killed buffer> - Command: rename-buffer NEWNAME &optional UNIQUE This function renames the current buffer to NEWNAME. An error is signaled if NEWNAME is not a string, or if there is already a buffer with that name. The function returns `nil'. Ordinarily, `rename-buffer' signals an error if NEWNAME is already in use. However, if UNIQUE is non-`nil', it modifies NEWNAME to make a name that is not in use. Interactively, you can make UNIQUE non-`nil' with a numeric prefix argument. One application of this command is to rename the `*shell*' buffer to some other name, thus making it possible to create a second shell buffer under the name `*shell*'. - Function: get-buffer BUFFER-OR-NAME This function returns the buffer specified by BUFFER-OR-NAME. If BUFFER-OR-NAME is a string and there is no buffer with that name, the value is `nil'. If 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: (setq b (get-buffer "lewis")) => #<buffer lewis> (get-buffer b) => #<buffer lewis> (get-buffer "Frazzle-nots") => nil See also the function `get-buffer-create' in *Note Creating Buffers::. - Function: generate-new-buffer-name STARTING-NAME &optional IGNORE This function returns a name that would be unique for a new buffer--but does not create the buffer. It starts with STARTING-NAME, and produces a name not currently in use for any buffer by appending a number inside of `<...>'. If IGNORE is given, it specifies a name that is okay to use (if it is in the sequence to be tried), even if a buffer with that name exists. See the related function `generate-new-buffer' in *Note Creating Buffers::. File: lispref.info, Node: Buffer File Name, Next: Buffer Modification, Prev: Buffer Names, Up: Buffers Buffer File Name ================ The "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 `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. *Note Visiting Files::. - Function: buffer-file-name &optional BUFFER This function returns the absolute file name of the file that BUFFER is visiting. If BUFFER is not visiting any file, `buffer-file-name' returns `nil'. If BUFFER is not supplied, it defaults to the current buffer. (buffer-file-name (other-buffer)) => "/usr/user/lewis/manual/files.texi" - Variable: buffer-file-name This buffer-local variable contains the name of the file being visited in the current buffer, or `nil' if it is not visiting a file. It is a permanent local, unaffected by `kill-local-variables'. buffer-file-name => "/usr/user/lewis/manual/buffers.texi" It is risky to change this variable's value without doing various other things. See the definition of `set-visited-file-name' in `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 XEmacs. - Variable: buffer-file-truename This buffer-local variable holds the truename of the file visited in the current buffer, or `nil' if no file is visited. It is a permanent local, unaffected by `kill-local-variables'. *Note Truenames::. - Variable: buffer-file-number This buffer-local variable holds the file number and directory device number of the file visited in the current buffer, or `nil' if no file or a nonexistent file is visited. It is a permanent local, unaffected by `kill-local-variables'. *Note Truenames::. The value is normally a list of the form `(FILENUM DEVNUM)'. This pair of numbers uniquely identifies the file among all files accessible on the system. See the function `file-attributes', in *Note File Attributes::, for more information about them. - Function: get-file-buffer FILENAME This function returns the buffer visiting file FILENAME. If there is no such buffer, it returns `nil'. The argument FILENAME, which must be a string, is expanded (*note File Name Expansion::.), then compared against the visited file names of all live buffers. (get-file-buffer "buffers.texi") => #<buffer buffers.texi> 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. - Command: set-visited-file-name FILENAME If FILENAME is a non-empty string, this function changes the name of the file visited in current buffer to FILENAME. (If the buffer had no visited file, this gives it one.) The *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 XEmacs knows) match the contents of FILENAME, even if it matched the former visited file. If FILENAME is `nil' or the empty string, that stands for "no visited file". In this case, `set-visited-file-name' marks the buffer as having no visited file. When the function `set-visited-file-name' is called interactively, it prompts for FILENAME in the minibuffer. See also `clear-visited-file-modtime' and `verify-visited-file-modtime' in *Note Buffer Modification::. - Variable: 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. File: lispref.info, Node: Buffer Modification, Next: Modification Time, Prev: Buffer File Name, Up: Buffers Buffer Modification =================== XEmacs keeps a flag called the "modified flag" for each buffer, to record whether you have changed the text of the buffer. This flag is set to `t' whenever you alter the contents of the buffer, and cleared to `nil' when you save it. Thus, the flag shows whether there are unsaved changes. The flag value is normally shown in the modeline (*note Modeline Variables::.), and controls saving (*note Saving Buffers::.) and auto-saving (*note Auto-Saving::.). Some Lisp programs set the flag explicitly. For example, the function `set-visited-file-name' sets the flag to `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 *Note Text::. - Function: buffer-modified-p &optional BUFFER This function returns `t' if the buffer BUFFER has been modified since it was last read in from a file or saved, or `nil' otherwise. If BUFFER is not supplied, the current buffer is tested. - Function: set-buffer-modified-p FLAG This function marks the current buffer as modified if FLAG is non-`nil', or as unmodified if the flag is `nil'. Another effect of calling this function is to cause unconditional redisplay of the modeline for the current buffer. In fact, the function `redraw-modeline' works by doing this: (set-buffer-modified-p (buffer-modified-p)) - Command: not-modified &optional ARG This command marks the current buffer as unmodified, and not needing to be saved. (If ARG is non-`nil', the buffer is instead marked as modified.) Don't use this function in programs, since it prints a message in the echo area; use `set-buffer-modified-p' (above) instead. - Function: buffer-modified-tick &optional BUFFER This function returns BUFFER`s modification-count. This is a counter that increments every time the buffer is modified. If BUFFER is `nil' (or omitted), the current buffer is used. File: lispref.info, Node: Modification Time, Next: Read Only Buffers, Prev: Buffer Modification, Up: Buffers Comparison of Modification Time =============================== 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. XEmacs therefore checks the file's modification time using the functions described below before saving the file. - Function: verify-visited-file-modtime BUFFER This function compares what 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 XEmacs visited or saved it. The function returns `t' if the last actual modification time and XEmacs's recorded modification time are the same, `nil' otherwise. - Function: 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 `set-visited-file-name' and other exceptional places where the usual test to avoid overwriting a changed file should not be done. - Function: visited-file-modtime This function returns the buffer's recorded last file modification time, as a list of the form `(HIGH . LOW)'. (This is the same format that `file-attributes' uses to return time values; see *Note File Attributes::.) - Function: 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 TIME if TIME is not `nil', and otherwise to the last modification time of the visited file. If TIME is not `nil', it should have the form `(HIGH . LOW)' or `(HIGH 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. - Function: ask-user-about-supersession-threat FILENAME This function is used to ask a user how to proceed after an attempt to modify an obsolete buffer visiting file FILENAME. An "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. 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 `file-supersession' error with data `(FILENAME)', in which case the proposed buffer modification is not allowed. This function is called automatically by XEmacs on the proper occasions. It exists so you can customize XEmacs by redefining it. See the file `userlock.el' for the standard definition. See also the file locking mechanism in *Note File Locks::. File: lispref.info, Node: Read Only Buffers, Next: The Buffer List, Prev: Modification Time, Up: Buffers Read-Only Buffers ================= If a buffer is "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: * 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 `C-x C-q'. * 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 `buffer-read-only' to `nil' (with `let') or bind `inhibit-read-only' to `t' around the places where they change the text. - Variable: buffer-read-only This buffer-local variable specifies whether the buffer is read-only. The buffer is read-only if this variable is non-`nil'. - Variable: inhibit-read-only If this variable is non-`nil', then read-only buffers and read-only characters may be modified. Read-only characters in a buffer are those that have non-`nil' `read-only' properties (either text properties or extent properties). *Note Extent Properties::, for more information about text properties and extent properties. If `inhibit-read-only' is `t', all `read-only' character properties have no effect. If `inhibit-read-only' is a list, then `read-only' character properties have no effect if they are members of the list (comparison is done with `eq'). - 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 `buffer-read-only' explicitly to the proper value, `t' or `nil'. - Function: barf-if-buffer-read-only This function signals a `buffer-read-only' error if the current buffer is read-only. *Note Interactive Call::, for another way to signal an error if the current buffer is read-only. File: lispref.info, Node: The Buffer List, Next: Creating Buffers, Prev: Read Only Buffers, Up: Buffers The Buffer List =============== The "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 `other-buffer', use this ordering. A buffer list displayed for the user also follows this order. Every frame has its own order for the buffer list. Switching to a new buffer inside of a particular frame changes the buffer list order for that frame, but does not affect the buffer list order of any other frames. In addition, there is a global, non-frame buffer list order that is independent of the buffer list orders for any particular frame. Note that the different buffer lists all contain the same elements. It is only the order of those elements that is different. - Function: buffer-list &optional FRAME This function returns a list of all buffers, including those whose names begin with a space. The elements are actual buffers, not their names. The order of the list is specific to FRAME, which defaults to the current frame. If FRAME is `t', the global, non-frame ordering is returned instead. (buffer-list) => (#<buffer buffers.texi> #<buffer *Minibuf-1*> #<buffer buffer.c> #<buffer *Help*> #<buffer TAGS>) ;; Note that the name of the minibuffer ;; begins with a space! (mapcar (function buffer-name) (buffer-list)) => ("buffers.texi" " *Minibuf-1*" "buffer.c" "*Help*" "TAGS") Buffers appear earlier in the list if they were current more recently. This list is a copy of a list used inside XEmacs; modifying it has no effect on the buffers. - Function: other-buffer &optional BUFFER-OR-NAME FRAME This function returns the first buffer in the buffer list other than BUFFER-OR-NAME, in FRAME's ordering for the buffer list. (FRAME defaults to the current frame. If FRAME is `t', then the global, non-frame ordering is used.) Usually this is the buffer most recently shown in the selected window, aside from BUFFER-OR-NAME. Buffers are moved to the front of the list when they are selected and to the end when they are buried. Buffers whose names start with a space are not considered. If BUFFER-OR-NAME is not supplied (or if it is not a buffer), then `other-buffer' returns the first buffer on the buffer list that is not visible in any window in a visible frame. If the selected frame has a non-`nil' `buffer-predicate' parameter, then `other-buffer' uses that predicate to decide which buffers to consider. It calls the predicate once for each buffer, and if the value is `nil', that buffer is ignored. *Note X Frame Parameters::. Note that the FRAME argument has a different interpretation in FSF Emacs 19. If no suitable buffer exists, the buffer `*scratch*' is returned (and created, if necessary). - Command: list-buffers &optional FILES-ONLY This function displays a listing of the names of existing buffers. It clears the buffer `*Buffer List*', then inserts the listing into that buffer and displays it in a window. `list-buffers' is intended for interactive use, and is described fully in `The XEmacs Reference Manual'. It returns `nil'. - Command: bury-buffer &optional BUFFER-OR-NAME This function puts 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 `other-buffer' to return. If BUFFER-OR-NAME is `nil' or omitted, this means to bury the current buffer. In addition, if the buffer is displayed in the selected window, this switches to some other buffer (obtained using `other-buffer') in the selected window. But if the buffer is displayed in some other window, it remains displayed there. If you wish to replace a buffer in all the windows that display it, use `replace-buffer-in-windows'. *Note Buffers and Windows::. File: lispref.info, Node: Creating Buffers, Next: Killing Buffers, Prev: The Buffer List, Up: Buffers Creating Buffers ================ This section describes the two primitives for creating buffers. `get-buffer-create' creates a buffer if it finds no existing buffer with the specified name; `generate-new-buffer' always creates a new buffer and gives it a unique name. Other functions you can use to create buffers include `with-output-to-temp-buffer' (*note Temporary Displays::.) and `create-file-buffer' (*note Visiting Files::.). Starting a subprocess can also create a buffer (*note Processes::.). - Function: get-buffer-create NAME This function returns a buffer named 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 NAME is not a string. (get-buffer-create "foo") => #<buffer foo> The major mode for the new buffer is set to Fundamental mode. The variable `default-major-mode' is handled at a higher level. *Note Auto Major Mode::. - Function: generate-new-buffer NAME This function returns a newly created, empty buffer, but does not make it current. If there is no buffer named NAME, then that is the name of the new buffer. If that name is in use, this function adds suffixes of the form `<N>' to NAME, where N is an integer. It tries successive integers starting with 2 until it finds an available name. An error is signaled if NAME is not a string. (generate-new-buffer "bar") => #<buffer bar> (generate-new-buffer "bar") => #<buffer bar<2>> (generate-new-buffer "bar") => #<buffer bar<3>> The major mode for the new buffer is set to Fundamental mode. The variable `default-major-mode' is handled at a higher level. *Note Auto Major Mode::. See the related function `generate-new-buffer-name' in *Note Buffer Names::. File: lispref.info, Node: Killing Buffers, Next: Indirect Buffers, Prev: Creating Buffers, Up: Buffers Killing Buffers =============== "Killing a buffer" makes its name unknown to XEmacs and makes its text space available for other use. The buffer object for the buffer that has been killed remains in existence as long as anything refers to it, but it is specially marked so that you cannot make it current or display it. Killed buffers retain their identity, however; two distinct buffers, when killed, remain distinct according to `eq'. If you kill a buffer that is current or displayed in a window, XEmacs 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). *Note Current Buffer::. If you kill a buffer that is the base buffer of one or more indirect buffers, the indirect buffers are automatically killed as well. The `buffer-name' of a killed buffer is `nil'. To test whether a buffer has been killed, you can either use this feature or the function `buffer-live-p'. - Function: buffer-live-p BUFFER This function returns `nil' if BUFFER is deleted, and `t' otherwise. - Command: kill-buffer BUFFER-OR-NAME This function kills the buffer 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 `nil'. Any processes that have this buffer as the `process-buffer' are sent the `SIGHUP' signal, which normally causes them to terminate. (The basic meaning of `SIGHUP' is that a dialup line has been disconnected.) *Note Deleting Processes::. If the buffer is visiting a file and contains unsaved changes, `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 `kill-buffer'. *Note Buffer Modification::. Killing a buffer that is already dead has no effect. (kill-buffer "foo.unchanged") => nil (kill-buffer "foo.changed") ---------- Buffer: Minibuffer ---------- Buffer foo.changed modified; kill anyway? (yes or no) `yes' ---------- Buffer: Minibuffer ---------- => nil - Variable: kill-buffer-query-functions After confirming unsaved changes, `kill-buffer' calls the functions in the list `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 `nil', `kill-buffer' spares the buffer's life. - Variable: kill-buffer-hook This is a normal hook run by `kill-buffer' after asking all the questions it is going to ask, just before actually killing the buffer. The buffer to be killed is current when the hook functions run. *Note Hooks::. - Variable: buffer-offer-save This variable, if non-`nil' in a particular buffer, tells `save-buffers-kill-emacs' and `save-some-buffers' to offer to save that buffer, just as they offer to save file-visiting buffers. The variable `buffer-offer-save' automatically becomes buffer-local when set for any reason. *Note Buffer-Local Variables::. File: lispref.info, Node: Indirect Buffers, Prev: Killing Buffers, Up: Buffers Indirect Buffers ================ An "indirect buffer" shares the text of some other buffer, which is called the "base buffer" of the indirect buffer. In some ways it is the analogue, for buffers, of a symbolic link among files. The base buffer may not itself be an indirect buffer. The text of the indirect buffer is always identical to the text of its base buffer; changes made by editing either one are visible immediately in the other. This includes the text properties as well as the characters themselves. But in all other respects, the indirect buffer and its base buffer are completely separate. They have different names, different values of point, different narrowing, different markers and overlays (though inserting or deleting text in either buffer relocates the markers and overlays for both), different major modes, and different local variables. An indirect buffer cannot visit a file, but its base buffer can. If you try to save the indirect buffer, that actually works by saving the base buffer. Killing an indirect buffer has no effect on its base buffer. Killing the base buffer effectively kills the indirect buffer in that it cannot ever again be the current buffer. - Command: make-indirect-buffer BASE-BUFFER NAME This creates an indirect buffer named NAME whose base buffer is BASE-BUFFER. The argument BASE-BUFFER may be a buffer or a string. If BASE-BUFFER is an indirect buffer, its base buffer is used as the base for the new buffer. - Function: buffer-base-buffer BUFFER This function returns the base buffer of BUFFER. If BUFFER is not indirect, the value is `nil'. Otherwise, the value is another buffer, which is never an indirect buffer. File: lispref.info, Node: Windows, Next: Frames, Prev: Buffers, Up: Top Windows ******* This chapter describes most of the functions and variables related to Emacs windows. See *Note 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. * Position of Window:: Accessing the position of a window. * Resizing Windows:: Changing the size of a window. * Window Configurations:: Saving and restoring the state of the screen. File: lispref.info, Node: Basic Windows, Next: Splitting Windows, Up: Windows Basic Concepts of Emacs Windows =============================== A "window" in XEmacs is the physical area of the screen in which a buffer is displayed. The term is also used to refer to a Lisp object that represents that screen area in Emacs Lisp. It should be clear from the context which is meant. XEmacs groups windows into frames. A frame represents an area of screen available for XEmacs to use. Each frame always contains at least one window, but you can subdivide it vertically or horizontally into multiple nonoverlapping Emacs windows. In each frame, at any time, one and only one window is designated as "selected within the frame". The frame's cursor appears in that window. At ant time, one frame is the selected frame; and the window selected within that frame is "the selected window". The selected window's buffer is usually the current buffer (except when `set-buffer' has been used). *Note Current Buffer::. For practical purposes, a window exists only while it is displayed in a frame. Once removed from the frame, the window is effectively deleted and should not be used, *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. (*Note Deleting Windows::.) Each window has the following attributes: * containing frame * window height * window width * window edges with respect to the frame or screen * the buffer it displays * position within the buffer at the upper left of the window * amount of horizontal scrolling, in columns * point * the mark * how recently the window was selected 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 display related 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 XEmacs is similar to what it means in the context of general-purpose window systems such as X, but not identical. The X Window System places X windows on the screen; XEmacs uses one or more X windows as frames, and subdivides them into Emacs windows. When you use XEmacs on a character-only terminal, XEmacs treats the whole terminal screen as one frame. Most window systems support arbitrarily located overlapping windows. In contrast, Emacs windows are "tiled"; they never overlap, and together they fill the whole screen or frame. Because of the way in which XEmacs creates new windows and resizes them, you can't create every conceivable tiling of windows on an Emacs frame. *Note Splitting Windows::, and *Note Size of Window::. *Note Display::, for information on how the contents of the window's buffer are displayed in the window. - Function: windowp OBJECT This function returns `t' if OBJECT is a window. File: lispref.info, Node: Splitting Windows, Next: Deleting Windows, Prev: Basic Windows, Up: Windows Splitting Windows ================= 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: `pop-to-buffer' and `display-buffer' (*note 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. - Function: one-window-p &optional NO-MINI ALL-FRAMES This function returns non-`nil' if there is only one window. The argument NO-MINI, if non-`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 ALL-FRAME controls which set of windows are counted. * If it is `nil' or omitted, then count only the selected frame, plus the minibuffer it uses (which may be on another frame). * If it is `t', then windows on all frames that currently exist (including invisible and iconified frames) are counted. * If it is the symbol `visible', then windows on all visible frames are counted. * If it is the number 0, then windows on all visible and iconified frames are counted. * If it is any other value, then precisely the windows in WINDOW's frame are counted, excluding the minibuffer in use if it lies in some other frame. - Command: split-window &optional WINDOW SIZE HORIZONTAL This function splits WINDOW into two windows. The original window 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 HORIZONTAL is non-`nil', then WINDOW splits into two side by side windows. The original window WINDOW keeps the leftmost SIZE columns, and gives the rest of the columns to the new window. Otherwise, it splits into windows one above the other, and WINDOW keeps the upper SIZE lines and gives the rest of the lines to the new window. The original window is therefore the left-hand or upper of the two, and the new window is the right-hand or lower. If WINDOW is omitted or `nil', then the selected window is split. If SIZE is omitted or `nil', then WINDOW is divided evenly into two parts. (If there is an odd line, it is allocated to the new window.) When `split-window' is called interactively, all its arguments are `nil'. The following example starts with one window on a frame that is 50 lines high by 80 columns wide; then the window is split. (setq w (selected-window)) => #<window 8 on windows.texi> (window-edges) ; Edges in order: => (0 0 80 50) ; left--top--right--bottom ;; Returns window created (setq w2 (split-window w 15)) => #<window 28 on windows.texi> (window-edges w2) => (0 15 80 50) ; Bottom window; ; top is line 15 (window-edges w) => (0 0 80 15) ; Top window The frame looks like this: __________ | | line 0 | w | |__________| | | line 15 | w2 | |__________| line 50 column 0 column 80 Next, the top window is split horizontally: (setq w3 (split-window w 35 t)) => #<window 32 on windows.texi> (window-edges w3) => (35 0 80 15) ; Left edge at column 35 (window-edges w) => (0 0 35 15) ; Right edge at column 35 (window-edges w2) => (0 15 80 50) ; Bottom window unchanged Now, the screen looks like this: column 35 __________ | | | line 0 | w | w3 | |___|______| | | line 15 | w2 | |__________| line 50 column 0 column 80 Normally, Emacs indicates the border between two side-by-side windows with a scroll bar (*note Scroll Bars: X Frame Parameters.) or `|' characters. The display table can specify alternative border characters; see *Note Display Tables::. - Command: split-window-vertically &optional SIZE This function splits the selected window into two windows, one above the other, leaving the selected window with SIZE lines. This function is simply an interface to `split-windows'. Here is the complete function definition for it: (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)))) - Command: split-window-horizontally &optional SIZE This function splits the selected window into two windows side-by-side, leaving the selected window with SIZE columns. This function is simply an interface to `split-windows'. Here is the complete definition for `split-window-horizontally' (except for part of the documentation string): (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)) - Function: one-window-p &optional NO-MINI ALL-FRAMES This function returns non-`nil' if there is only one window. The argument NO-MINI, if non-`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 ALL-FRAMES specifies which frames to consider. Here are the possible values and their meanings: `nil' Count the windows in the selected frame, plus the minibuffer used by that frame even if it lies in some other frame. `t' Count all windows in all existing frames. `visible' Count all windows in all visible frames. 0 Count all windows in all visible or iconified frames. anything else Count precisely the windows in the selected frame, and no others. File: lispref.info, Node: Deleting Windows, Next: Selecting Windows, Prev: Splitting Windows, Up: Windows Deleting Windows ================ A window remains visible on its frame unless you "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 (*note 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.) - Function: window-live-p WINDOW This function returns `nil' if WINDOW is deleted, and `t' otherwise. *Warning:* Erroneous information or fatal errors may result from using a deleted window as if it were live. - Command: delete-window &optional WINDOW This function removes WINDOW from the display. If WINDOW is omitted, then the selected window is deleted. An error is signaled if there is only one window when `delete-window' is called. This function returns `nil'. When `delete-window' is called interactively, WINDOW defaults to the selected window. - Command: delete-other-windows &optional WINDOW This function makes WINDOW the only window on its frame, by deleting the other windows in that frame. If WINDOW is omitted or `nil', then the selected window is used by default. The result is `nil'. - Command: delete-windows-on BUFFER &optional FRAME This function deletes all windows showing BUFFER. If there are no windows showing BUFFER, it does nothing. `delete-windows-on' operates frame by frame. If a frame has several windows showing different buffers, then those showing BUFFER are removed, and the others expand to fill the space. If all windows in some frame are showing BUFFER (including the case where there is only one window), then the frame reverts to having a single window showing another buffer chosen with `other-buffer'. *Note The Buffer List::. The argument FRAME controls which frames to operate on: * If it is `nil', operate on the selected frame. * If it is `t', operate on all frames. * If it is `visible', operate on all visible frames. * 0 If it is 0, operate on all visible or iconified frames. * If it is a frame, operate on that frame. This function always returns `nil'. File: lispref.info, Node: Selecting Windows, Next: Cyclic Window Ordering, Prev: Deleting Windows, Up: Windows Selecting Windows ================= When a window is selected, the buffer in the window becomes the current buffer, and the cursor will appear in it. - Function: selected-window &optional DEVICE This function returns the selected window. This is the window in which the cursor appears and to which many commands apply. Each separate device can have its own selected window, which is remembered as focus changes from device to device. Optional argument DEVICE specifies which device to return the selected window for, and defaults to the selected device. - Function: select-window WINDOW This function makes WINDOW the selected window. The cursor then appears in WINDOW (on redisplay). The buffer being displayed in WINDOW is immediately designated the current buffer. The return value is WINDOW. (setq w (next-window)) (select-window w) => #<window 65 on windows.texi> - Macro: save-selected-window FORMS... This macro records the selected window, executes FORMS in sequence, then restores the earlier selected window. It does not save or restore anything about the sizes, arrangement or contents of windows; therefore, if the FORMS change them, the changes are permanent. The following functions choose one of the windows on the screen, offering various criteria for the choice. - Function: 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 FRAME controls which windows are considered. * If it is `nil', consider windows on the selected frame. * If it is `t', consider windows on all frames. * If it is `visible', consider windows on all visible frames. * If it is 0, consider windows on all visible or iconified frames. * If it is a frame, consider windows on that frame. - Function: 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 that is first in the cyclic ordering of windows (see following section), starting from the selected window. The argument FRAME controls which set of windows are considered. See `get-lru-window', above.