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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
3 | @c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999, 2001, 2002, | |
6ed161e1 | 4 | @c 2003, 2004, 2005, 2006, 2007, 2008, 2009 Free Software Foundation, Inc. |
b8d4c8d0 | 5 | @c See the file elisp.texi for copying conditions. |
6336d8c3 | 6 | @setfilename ../../info/buffers |
b8d4c8d0 GM |
7 | @node Buffers, Windows, Backups and Auto-Saving, Top |
8 | @chapter Buffers | |
9 | @cindex buffer | |
10 | ||
11 | A @dfn{buffer} is a Lisp object containing text to be edited. Buffers | |
12 | are used to hold the contents of files that are being visited; there may | |
13 | also be buffers that are not visiting files. While several buffers may | |
14 | exist at one time, only one buffer is designated the @dfn{current | |
15 | buffer} at any time. Most editing commands act on the contents of the | |
16 | current buffer. Each buffer, including the current buffer, may or may | |
17 | not be displayed in any windows. | |
18 | ||
19 | @menu | |
20 | * Buffer Basics:: What is a buffer? | |
21 | * Current Buffer:: Designating a buffer as current | |
22 | so that primitives will access its contents. | |
23 | * Buffer Names:: Accessing and changing buffer names. | |
24 | * Buffer File Name:: The buffer file name indicates which file is visited. | |
25 | * Buffer Modification:: A buffer is @dfn{modified} if it needs to be saved. | |
26 | * Modification Time:: Determining whether the visited file was changed | |
27 | ``behind Emacs's back''. | |
28 | * Read Only Buffers:: Modifying text is not allowed in a read-only buffer. | |
29 | * The Buffer List:: How to look at all the existing buffers. | |
30 | * Creating Buffers:: Functions that create buffers. | |
31 | * Killing Buffers:: Buffers exist until explicitly killed. | |
32 | * Indirect Buffers:: An indirect buffer shares text with some other buffer. | |
2aaaf0dd | 33 | * Swapping Text:: Swapping text between two buffers. |
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34 | * Buffer Gap:: The gap in the buffer. |
35 | @end menu | |
36 | ||
37 | @node Buffer Basics | |
38 | @comment node-name, next, previous, up | |
39 | @section Buffer Basics | |
40 | ||
41 | @ifnottex | |
42 | A @dfn{buffer} is a Lisp object containing text to be edited. Buffers | |
43 | are used to hold the contents of files that are being visited; there may | |
44 | also be buffers that are not visiting files. Although several buffers | |
45 | normally exist, only one buffer is designated the @dfn{current | |
46 | buffer} at any time. Most editing commands act on the contents of the | |
47 | current buffer. Each buffer, including the current buffer, may or may | |
48 | not be displayed in any windows. | |
49 | @end ifnottex | |
50 | ||
51 | Buffers in Emacs editing are objects that have distinct names and hold | |
52 | text that can be edited. Buffers appear to Lisp programs as a special | |
53 | data type. You can think of the contents of a buffer as a string that | |
54 | you can extend; insertions and deletions may occur in any part of the | |
55 | buffer. @xref{Text}. | |
56 | ||
57 | A Lisp buffer object contains numerous pieces of information. Some of | |
58 | this information is directly accessible to the programmer through | |
59 | variables, while other information is accessible only through | |
60 | special-purpose functions. For example, the visited file name is | |
61 | directly accessible through a variable, while the value of point is | |
62 | accessible only through a primitive function. | |
63 | ||
64 | Buffer-specific information that is directly accessible is stored in | |
65 | @dfn{buffer-local} variable bindings, which are variable values that are | |
66 | effective only in a particular buffer. This feature allows each buffer | |
67 | to override the values of certain variables. Most major modes override | |
68 | variables such as @code{fill-column} or @code{comment-column} in this | |
69 | way. For more information about buffer-local variables and functions | |
70 | related to them, see @ref{Buffer-Local Variables}. | |
71 | ||
72 | For functions and variables related to visiting files in buffers, see | |
73 | @ref{Visiting Files} and @ref{Saving Buffers}. For functions and | |
74 | variables related to the display of buffers in windows, see | |
75 | @ref{Buffers and Windows}. | |
76 | ||
77 | @defun bufferp object | |
78 | This function returns @code{t} if @var{object} is a buffer, | |
79 | @code{nil} otherwise. | |
80 | @end defun | |
81 | ||
82 | @node Current Buffer | |
83 | @section The Current Buffer | |
84 | @cindex selecting a buffer | |
85 | @cindex changing to another buffer | |
86 | @cindex current buffer | |
87 | ||
88 | There are, in general, many buffers in an Emacs session. At any time, | |
89 | one of them is designated as the @dfn{current buffer}. This is the | |
90 | buffer in which most editing takes place, because most of the primitives | |
91 | for examining or changing text in a buffer operate implicitly on the | |
92 | current buffer (@pxref{Text}). Normally the buffer that is displayed on | |
93 | the screen in the selected window is the current buffer, but this is not | |
94 | always so: a Lisp program can temporarily designate any buffer as | |
95 | current in order to operate on its contents, without changing what is | |
96 | displayed on the screen. | |
97 | ||
98 | The way to designate a current buffer in a Lisp program is by calling | |
99 | @code{set-buffer}. The specified buffer remains current until a new one | |
100 | is designated. | |
101 | ||
102 | When an editing command returns to the editor command loop, the | |
103 | command loop designates the buffer displayed in the selected window as | |
104 | current, to prevent confusion: the buffer that the cursor is in when | |
105 | Emacs reads a command is the buffer that the command will apply to. | |
106 | (@xref{Command Loop}.) Therefore, @code{set-buffer} is not the way to | |
107 | switch visibly to a different buffer so that the user can edit it. For | |
108 | that, you must use the functions described in @ref{Displaying Buffers}. | |
109 | ||
110 | @strong{Warning:} Lisp functions that change to a different current buffer | |
111 | should not depend on the command loop to set it back afterwards. | |
112 | Editing commands written in Emacs Lisp can be called from other programs | |
113 | as well as from the command loop; it is convenient for the caller if | |
114 | the subroutine does not change which buffer is current (unless, of | |
115 | course, that is the subroutine's purpose). Therefore, you should | |
116 | normally use @code{set-buffer} within a @code{save-current-buffer} or | |
117 | @code{save-excursion} (@pxref{Excursions}) form that will restore the | |
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118 | current buffer when your function is done. Here, as an example, is a |
119 | simplified version of the command @code{append-to-buffer}: | |
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120 | |
121 | @example | |
122 | @group | |
123 | (defun append-to-buffer (buffer start end) | |
9257072f | 124 | "Append to specified buffer the text of the region." |
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125 | (interactive "BAppend to buffer: \nr") |
126 | (let ((oldbuf (current-buffer))) | |
127 | (save-current-buffer | |
128 | (set-buffer (get-buffer-create buffer)) | |
129 | (insert-buffer-substring oldbuf start end)))) | |
130 | @end group | |
131 | @end example | |
132 | ||
133 | @noindent | |
134 | This function binds a local variable to record the current buffer, and | |
135 | then @code{save-current-buffer} arranges to make it current again. | |
136 | Next, @code{set-buffer} makes the specified buffer current. Finally, | |
137 | @code{insert-buffer-substring} copies the string from the original | |
138 | current buffer to the specified (and now current) buffer. | |
139 | ||
140 | If the buffer appended to happens to be displayed in some window, | |
141 | the next redisplay will show how its text has changed. Otherwise, you | |
142 | will not see the change immediately on the screen. The buffer becomes | |
143 | current temporarily during the execution of the command, but this does | |
144 | not cause it to be displayed. | |
145 | ||
146 | If you make local bindings (with @code{let} or function arguments) for | |
147 | a variable that may also have buffer-local bindings, make sure that the | |
148 | same buffer is current at the beginning and at the end of the local | |
149 | binding's scope. Otherwise you might bind it in one buffer and unbind | |
150 | it in another! There are two ways to do this. In simple cases, you may | |
151 | see that nothing ever changes the current buffer within the scope of the | |
152 | binding. Otherwise, use @code{save-current-buffer} or | |
153 | @code{save-excursion} to make sure that the buffer current at the | |
154 | beginning is current again whenever the variable is unbound. | |
155 | ||
156 | Do not rely on using @code{set-buffer} to change the current buffer | |
157 | back, because that won't do the job if a quit happens while the wrong | |
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158 | buffer is current. For instance, in the previous example, it would |
159 | have been wrong to do this: | |
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160 | |
161 | @example | |
162 | @group | |
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163 | (let ((oldbuf (current-buffer))) |
164 | (set-buffer (get-buffer-create buffer)) | |
165 | (insert-buffer-substring oldbuf start end) | |
166 | (set-buffer oldbuf)) | |
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167 | @end group |
168 | @end example | |
169 | ||
170 | @noindent | |
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171 | Using @code{save-current-buffer}, as we did, handles quitting, errors, |
172 | and @code{throw}, as well as ordinary evaluation. | |
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173 | |
174 | @defun current-buffer | |
175 | This function returns the current buffer. | |
176 | ||
177 | @example | |
178 | @group | |
179 | (current-buffer) | |
180 | @result{} #<buffer buffers.texi> | |
181 | @end group | |
182 | @end example | |
183 | @end defun | |
184 | ||
185 | @defun set-buffer buffer-or-name | |
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186 | This function makes @var{buffer-or-name} the current buffer. |
187 | @var{buffer-or-name} must be an existing buffer or the name of an | |
188 | existing buffer. The return value is the buffer made current. | |
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189 | |
190 | This function does not display the buffer in any window, so the user | |
191 | cannot necessarily see the buffer. But Lisp programs will now operate | |
192 | on it. | |
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193 | @end defun |
194 | ||
195 | @defspec save-current-buffer body@dots{} | |
196 | The @code{save-current-buffer} special form saves the identity of the | |
197 | current buffer, evaluates the @var{body} forms, and finally restores | |
198 | that buffer as current. The return value is the value of the last | |
199 | form in @var{body}. The current buffer is restored even in case of an | |
200 | abnormal exit via @code{throw} or error (@pxref{Nonlocal Exits}). | |
201 | ||
202 | If the buffer that used to be current has been killed by the time of | |
203 | exit from @code{save-current-buffer}, then it is not made current again, | |
204 | of course. Instead, whichever buffer was current just before exit | |
205 | remains current. | |
206 | @end defspec | |
207 | ||
208 | @defmac with-current-buffer buffer-or-name body@dots{} | |
209 | The @code{with-current-buffer} macro saves the identity of the current | |
210 | buffer, makes @var{buffer-or-name} current, evaluates the @var{body} | |
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211 | forms, and finally restores the current buffer. @var{buffer-or-name} |
212 | must specify an existing buffer or the name of an existing buffer. | |
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214 | The return value is the value of the last form in @var{body}. The |
215 | current buffer is restored even in case of an abnormal exit via | |
216 | @code{throw} or error (@pxref{Nonlocal Exits}). | |
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217 | @end defmac |
218 | ||
219 | @defmac with-temp-buffer body@dots{} | |
220 | @anchor{Definition of with-temp-buffer} | |
221 | The @code{with-temp-buffer} macro evaluates the @var{body} forms | |
222 | with a temporary buffer as the current buffer. It saves the identity of | |
223 | the current buffer, creates a temporary buffer and makes it current, | |
224 | evaluates the @var{body} forms, and finally restores the previous | |
225 | current buffer while killing the temporary buffer. By default, undo | |
226 | information (@pxref{Undo}) is not recorded in the buffer created by | |
227 | this macro (but @var{body} can enable that, if needed). | |
228 | ||
229 | The return value is the value of the last form in @var{body}. You can | |
230 | return the contents of the temporary buffer by using | |
231 | @code{(buffer-string)} as the last form. | |
232 | ||
233 | The current buffer is restored even in case of an abnormal exit via | |
234 | @code{throw} or error (@pxref{Nonlocal Exits}). | |
235 | ||
236 | See also @code{with-temp-file} in @ref{Definition of with-temp-file,, | |
237 | Writing to Files}. | |
238 | @end defmac | |
239 | ||
240 | @node Buffer Names | |
241 | @section Buffer Names | |
242 | @cindex buffer names | |
243 | ||
244 | Each buffer has a unique name, which is a string. Many of the | |
245 | functions that work on buffers accept either a buffer or a buffer name | |
246 | as an argument. Any argument called @var{buffer-or-name} is of this | |
247 | sort, and an error is signaled if it is neither a string nor a buffer. | |
248 | Any argument called @var{buffer} must be an actual buffer | |
249 | object, not a name. | |
250 | ||
251 | @cindex hidden buffers | |
252 | @cindex buffers without undo information | |
253 | Buffers that are ephemeral and generally uninteresting to the user | |
254 | have names starting with a space, so that the @code{list-buffers} and | |
255 | @code{buffer-menu} commands don't mention them (but if such a buffer | |
256 | visits a file, it @strong{is} mentioned). A name starting with | |
257 | space also initially disables recording undo information; see | |
258 | @ref{Undo}. | |
259 | ||
260 | @defun buffer-name &optional buffer | |
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261 | This function returns the name of @var{buffer} as a string. |
262 | @var{buffer} defaults to the current buffer. | |
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263 | |
264 | If @code{buffer-name} returns @code{nil}, it means that @var{buffer} | |
265 | has been killed. @xref{Killing Buffers}. | |
266 | ||
267 | @example | |
268 | @group | |
269 | (buffer-name) | |
270 | @result{} "buffers.texi" | |
271 | @end group | |
272 | ||
273 | @group | |
274 | (setq foo (get-buffer "temp")) | |
275 | @result{} #<buffer temp> | |
276 | @end group | |
277 | @group | |
278 | (kill-buffer foo) | |
279 | @result{} nil | |
280 | @end group | |
281 | @group | |
282 | (buffer-name foo) | |
283 | @result{} nil | |
284 | @end group | |
285 | @group | |
286 | foo | |
287 | @result{} #<killed buffer> | |
288 | @end group | |
289 | @end example | |
290 | @end defun | |
291 | ||
292 | @deffn Command rename-buffer newname &optional unique | |
293 | This function renames the current buffer to @var{newname}. An error | |
294 | is signaled if @var{newname} is not a string. | |
295 | ||
296 | @c Emacs 19 feature | |
297 | Ordinarily, @code{rename-buffer} signals an error if @var{newname} is | |
298 | already in use. However, if @var{unique} is non-@code{nil}, it modifies | |
299 | @var{newname} to make a name that is not in use. Interactively, you can | |
300 | make @var{unique} non-@code{nil} with a numeric prefix argument. | |
301 | (This is how the command @code{rename-uniquely} is implemented.) | |
302 | ||
303 | This function returns the name actually given to the buffer. | |
304 | @end deffn | |
305 | ||
306 | @defun get-buffer buffer-or-name | |
307 | This function returns the buffer specified by @var{buffer-or-name}. | |
308 | If @var{buffer-or-name} is a string and there is no buffer with that | |
309 | name, the value is @code{nil}. If @var{buffer-or-name} is a buffer, it | |
310 | is returned as given; that is not very useful, so the argument is usually | |
311 | a name. For example: | |
312 | ||
313 | @example | |
314 | @group | |
315 | (setq b (get-buffer "lewis")) | |
316 | @result{} #<buffer lewis> | |
317 | @end group | |
318 | @group | |
319 | (get-buffer b) | |
320 | @result{} #<buffer lewis> | |
321 | @end group | |
322 | @group | |
323 | (get-buffer "Frazzle-nots") | |
324 | @result{} nil | |
325 | @end group | |
326 | @end example | |
327 | ||
328 | See also the function @code{get-buffer-create} in @ref{Creating Buffers}. | |
329 | @end defun | |
330 | ||
331 | @c Emacs 19 feature | |
332 | @defun generate-new-buffer-name starting-name &optional ignore | |
333 | This function returns a name that would be unique for a new buffer---but | |
334 | does not create the buffer. It starts with @var{starting-name}, and | |
335 | produces a name not currently in use for any buffer by appending a | |
336 | number inside of @samp{<@dots{}>}. It starts at 2 and keeps | |
337 | incrementing the number until it is not the name of an existing buffer. | |
338 | ||
339 | If the optional second argument @var{ignore} is non-@code{nil}, it | |
340 | should be a string, a potential buffer name. It means to consider | |
341 | that potential buffer acceptable, if it is tried, even it is the name | |
342 | of an existing buffer (which would normally be rejected). Thus, if | |
343 | buffers named @samp{foo}, @samp{foo<2>}, @samp{foo<3>} and | |
344 | @samp{foo<4>} exist, | |
345 | ||
346 | @example | |
347 | (generate-new-buffer-name "foo") | |
348 | @result{} "foo<5>" | |
349 | (generate-new-buffer-name "foo" "foo<3>") | |
350 | @result{} "foo<3>" | |
351 | (generate-new-buffer-name "foo" "foo<6>") | |
352 | @result{} "foo<5>" | |
353 | @end example | |
354 | ||
355 | See the related function @code{generate-new-buffer} in @ref{Creating | |
356 | Buffers}. | |
357 | @end defun | |
358 | ||
359 | @node Buffer File Name | |
360 | @section Buffer File Name | |
361 | @cindex visited file | |
362 | @cindex buffer file name | |
363 | @cindex file name of buffer | |
364 | ||
365 | The @dfn{buffer file name} is the name of the file that is visited in | |
366 | that buffer. When a buffer is not visiting a file, its buffer file name | |
367 | is @code{nil}. Most of the time, the buffer name is the same as the | |
368 | nondirectory part of the buffer file name, but the buffer file name and | |
369 | the buffer name are distinct and can be set independently. | |
370 | @xref{Visiting Files}. | |
371 | ||
372 | @defun buffer-file-name &optional buffer | |
373 | This function returns the absolute file name of the file that | |
374 | @var{buffer} is visiting. If @var{buffer} is not visiting any file, | |
375 | @code{buffer-file-name} returns @code{nil}. If @var{buffer} is not | |
376 | supplied, it defaults to the current buffer. | |
377 | ||
378 | @example | |
379 | @group | |
380 | (buffer-file-name (other-buffer)) | |
381 | @result{} "/usr/user/lewis/manual/files.texi" | |
382 | @end group | |
383 | @end example | |
384 | @end defun | |
385 | ||
386 | @defvar buffer-file-name | |
387 | This buffer-local variable contains the name of the file being visited | |
388 | in the current buffer, or @code{nil} if it is not visiting a file. It | |
389 | is a permanent local variable, unaffected by | |
390 | @code{kill-all-local-variables}. | |
391 | ||
392 | @example | |
393 | @group | |
394 | buffer-file-name | |
395 | @result{} "/usr/user/lewis/manual/buffers.texi" | |
396 | @end group | |
397 | @end example | |
398 | ||
399 | It is risky to change this variable's value without doing various other | |
400 | things. Normally it is better to use @code{set-visited-file-name} (see | |
401 | below); some of the things done there, such as changing the buffer name, | |
402 | are not strictly necessary, but others are essential to avoid confusing | |
403 | Emacs. | |
404 | @end defvar | |
405 | ||
406 | @defvar buffer-file-truename | |
407 | This buffer-local variable holds the abbreviated truename of the file | |
408 | visited in the current buffer, or @code{nil} if no file is visited. | |
409 | It is a permanent local, unaffected by | |
410 | @code{kill-all-local-variables}. @xref{Truenames}, and | |
411 | @ref{Definition of abbreviate-file-name}. | |
412 | @end defvar | |
413 | ||
414 | @defvar buffer-file-number | |
415 | This buffer-local variable holds the file number and directory device | |
416 | number of the file visited in the current buffer, or @code{nil} if no | |
417 | file or a nonexistent file is visited. It is a permanent local, | |
418 | unaffected by @code{kill-all-local-variables}. | |
419 | ||
420 | The value is normally a list of the form @code{(@var{filenum} | |
421 | @var{devnum})}. This pair of numbers uniquely identifies the file among | |
422 | all files accessible on the system. See the function | |
423 | @code{file-attributes}, in @ref{File Attributes}, for more information | |
424 | about them. | |
425 | ||
426 | If @code{buffer-file-name} is the name of a symbolic link, then both | |
427 | numbers refer to the recursive target. | |
428 | @end defvar | |
429 | ||
430 | @defun get-file-buffer filename | |
431 | This function returns the buffer visiting file @var{filename}. If | |
432 | there is no such buffer, it returns @code{nil}. The argument | |
433 | @var{filename}, which must be a string, is expanded (@pxref{File Name | |
434 | Expansion}), then compared against the visited file names of all live | |
435 | buffers. Note that the buffer's @code{buffer-file-name} must match | |
436 | the expansion of @var{filename} exactly. This function will not | |
437 | recognize other names for the same file. | |
438 | ||
439 | @example | |
440 | @group | |
441 | (get-file-buffer "buffers.texi") | |
442 | @result{} #<buffer buffers.texi> | |
443 | @end group | |
444 | @end example | |
445 | ||
446 | In unusual circumstances, there can be more than one buffer visiting | |
447 | the same file name. In such cases, this function returns the first | |
448 | such buffer in the buffer list. | |
449 | @end defun | |
450 | ||
451 | @defun find-buffer-visiting filename &optional predicate | |
452 | This is like @code{get-file-buffer}, except that it can return any | |
453 | buffer visiting the file @emph{possibly under a different name}. That | |
454 | is, the buffer's @code{buffer-file-name} does not need to match the | |
455 | expansion of @var{filename} exactly, it only needs to refer to the | |
456 | same file. If @var{predicate} is non-@code{nil}, it should be a | |
457 | function of one argument, a buffer visiting @var{filename}. The | |
458 | buffer is only considered a suitable return value if @var{predicate} | |
459 | returns non-@code{nil}. If it can not find a suitable buffer to | |
460 | return, @code{find-buffer-visiting} returns @code{nil}. | |
461 | @end defun | |
462 | ||
463 | @deffn Command set-visited-file-name filename &optional no-query along-with-file | |
464 | If @var{filename} is a non-empty string, this function changes the | |
465 | name of the file visited in the current buffer to @var{filename}. (If the | |
466 | buffer had no visited file, this gives it one.) The @emph{next time} | |
467 | the buffer is saved it will go in the newly-specified file. | |
468 | ||
469 | This command marks the buffer as modified, since it does not (as far | |
470 | as Emacs knows) match the contents of @var{filename}, even if it | |
471 | matched the former visited file. It also renames the buffer to | |
472 | correspond to the new file name, unless the new name is already in | |
473 | use. | |
474 | ||
475 | If @var{filename} is @code{nil} or the empty string, that stands for | |
476 | ``no visited file.'' In this case, @code{set-visited-file-name} marks | |
477 | the buffer as having no visited file, without changing the buffer's | |
478 | modified flag. | |
479 | ||
480 | Normally, this function asks the user for confirmation if there | |
481 | already is a buffer visiting @var{filename}. If @var{no-query} is | |
482 | non-@code{nil}, that prevents asking this question. If there already | |
483 | is a buffer visiting @var{filename}, and the user confirms or | |
484 | @var{query} is non-@code{nil}, this function makes the new buffer name | |
485 | unique by appending a number inside of @samp{<@dots{}>} to @var{filename}. | |
486 | ||
487 | If @var{along-with-file} is non-@code{nil}, that means to assume that | |
488 | the former visited file has been renamed to @var{filename}. In this | |
489 | case, the command does not change the buffer's modified flag, nor the | |
490 | buffer's recorded last file modification time as reported by | |
491 | @code{visited-file-modtime} (@pxref{Modification Time}). If | |
492 | @var{along-with-file} is @code{nil}, this function clears the recorded | |
493 | last file modification time, after which @code{visited-file-modtime} | |
494 | returns zero. | |
495 | ||
496 | @c Wordy to avoid overfull hbox. --rjc 16mar92 | |
497 | When the function @code{set-visited-file-name} is called interactively, it | |
498 | prompts for @var{filename} in the minibuffer. | |
499 | @end deffn | |
500 | ||
501 | @defvar list-buffers-directory | |
502 | This buffer-local variable specifies a string to display in a buffer | |
503 | listing where the visited file name would go, for buffers that don't | |
504 | have a visited file name. Dired buffers use this variable. | |
505 | @end defvar | |
506 | ||
507 | @node Buffer Modification | |
508 | @section Buffer Modification | |
509 | @cindex buffer modification | |
510 | @cindex modification flag (of buffer) | |
511 | ||
512 | Emacs keeps a flag called the @dfn{modified flag} for each buffer, to | |
513 | record whether you have changed the text of the buffer. This flag is | |
514 | set to @code{t} whenever you alter the contents of the buffer, and | |
515 | cleared to @code{nil} when you save it. Thus, the flag shows whether | |
516 | there are unsaved changes. The flag value is normally shown in the mode | |
517 | line (@pxref{Mode Line Variables}), and controls saving (@pxref{Saving | |
518 | Buffers}) and auto-saving (@pxref{Auto-Saving}). | |
519 | ||
520 | Some Lisp programs set the flag explicitly. For example, the function | |
521 | @code{set-visited-file-name} sets the flag to @code{t}, because the text | |
522 | does not match the newly-visited file, even if it is unchanged from the | |
523 | file formerly visited. | |
524 | ||
525 | The functions that modify the contents of buffers are described in | |
526 | @ref{Text}. | |
527 | ||
528 | @defun buffer-modified-p &optional buffer | |
529 | This function returns @code{t} if the buffer @var{buffer} has been modified | |
530 | since it was last read in from a file or saved, or @code{nil} | |
531 | otherwise. If @var{buffer} is not supplied, the current buffer | |
532 | is tested. | |
533 | @end defun | |
534 | ||
535 | @defun set-buffer-modified-p flag | |
536 | This function marks the current buffer as modified if @var{flag} is | |
537 | non-@code{nil}, or as unmodified if the flag is @code{nil}. | |
538 | ||
539 | Another effect of calling this function is to cause unconditional | |
540 | redisplay of the mode line for the current buffer. In fact, the | |
541 | function @code{force-mode-line-update} works by doing this: | |
542 | ||
543 | @example | |
544 | @group | |
545 | (set-buffer-modified-p (buffer-modified-p)) | |
546 | @end group | |
547 | @end example | |
548 | @end defun | |
549 | ||
550 | @defun restore-buffer-modified-p flag | |
551 | Like @code{set-buffer-modified-p}, but does not force redisplay | |
552 | of mode lines. | |
553 | @end defun | |
554 | ||
555 | @deffn Command not-modified &optional arg | |
556 | This command marks the current buffer as unmodified, and not needing | |
557 | to be saved. If @var{arg} is non-@code{nil}, it marks the buffer as | |
558 | modified, so that it will be saved at the next suitable occasion. | |
559 | Interactively, @var{arg} is the prefix argument. | |
560 | ||
561 | Don't use this function in programs, since it prints a message in the | |
562 | echo area; use @code{set-buffer-modified-p} (above) instead. | |
563 | @end deffn | |
564 | ||
565 | @defun buffer-modified-tick &optional buffer | |
566 | This function returns @var{buffer}'s modification-count. This is a | |
567 | counter that increments every time the buffer is modified. If | |
568 | @var{buffer} is @code{nil} (or omitted), the current buffer is used. | |
569 | The counter can wrap around occasionally. | |
570 | @end defun | |
571 | ||
572 | @defun buffer-chars-modified-tick &optional buffer | |
573 | This function returns @var{buffer}'s character-change modification-count. | |
574 | Changes to text properties leave this counter unchanged; however, each | |
575 | time text is inserted or removed from the buffer, the counter is reset | |
569382c2 | 576 | to the value that would be returned by @code{buffer-modified-tick}. |
b8d4c8d0 GM |
577 | By comparing the values returned by two @code{buffer-chars-modified-tick} |
578 | calls, you can tell whether a character change occurred in that buffer | |
579 | in between the calls. If @var{buffer} is @code{nil} (or omitted), the | |
580 | current buffer is used. | |
581 | @end defun | |
582 | ||
583 | @node Modification Time | |
584 | @comment node-name, next, previous, up | |
585 | @section Buffer Modification Time | |
586 | @cindex comparing file modification time | |
587 | @cindex modification time of buffer | |
588 | ||
589 | Suppose that you visit a file and make changes in its buffer, and | |
590 | meanwhile the file itself is changed on disk. At this point, saving the | |
591 | buffer would overwrite the changes in the file. Occasionally this may | |
592 | be what you want, but usually it would lose valuable information. Emacs | |
593 | therefore checks the file's modification time using the functions | |
594 | described below before saving the file. (@xref{File Attributes}, | |
595 | for how to examine a file's modification time.) | |
596 | ||
597 | @defun verify-visited-file-modtime buffer | |
598 | This function compares what @var{buffer} has recorded for the | |
599 | modification time of its visited file against the actual modification | |
600 | time of the file as recorded by the operating system. The two should be | |
601 | the same unless some other process has written the file since Emacs | |
602 | visited or saved it. | |
603 | ||
604 | The function returns @code{t} if the last actual modification time and | |
605 | Emacs's recorded modification time are the same, @code{nil} otherwise. | |
606 | It also returns @code{t} if the buffer has no recorded last | |
607 | modification time, that is if @code{visited-file-modtime} would return | |
608 | zero. | |
609 | ||
610 | It always returns @code{t} for buffers that are not visiting a file, | |
611 | even if @code{visited-file-modtime} returns a non-zero value. For | |
612 | instance, it always returns @code{t} for dired buffers. It returns | |
613 | @code{t} for buffers that are visiting a file that does not exist and | |
614 | never existed, but @code{nil} for file-visiting buffers whose file has | |
615 | been deleted. | |
616 | @end defun | |
617 | ||
618 | @defun clear-visited-file-modtime | |
619 | This function clears out the record of the last modification time of | |
620 | the file being visited by the current buffer. As a result, the next | |
621 | attempt to save this buffer will not complain of a discrepancy in | |
622 | file modification times. | |
623 | ||
624 | This function is called in @code{set-visited-file-name} and other | |
625 | exceptional places where the usual test to avoid overwriting a changed | |
626 | file should not be done. | |
627 | @end defun | |
628 | ||
629 | @c Emacs 19 feature | |
630 | @defun visited-file-modtime | |
631 | This function returns the current buffer's recorded last file | |
632 | modification time, as a list of the form @code{(@var{high} @var{low})}. | |
633 | (This is the same format that @code{file-attributes} uses to return | |
634 | time values; see @ref{File Attributes}.) | |
635 | ||
636 | If the buffer has no recorded last modification time, this function | |
637 | returns zero. This case occurs, for instance, if the buffer is not | |
638 | visiting a file or if the time has been explicitly cleared by | |
639 | @code{clear-visited-file-modtime}. Note, however, that | |
640 | @code{visited-file-modtime} returns a list for some non-file buffers | |
641 | too. For instance, in a Dired buffer listing a directory, it returns | |
642 | the last modification time of that directory, as recorded by Dired. | |
643 | ||
644 | For a new buffer visiting a not yet existing file, @var{high} is | |
645 | @minus{}1 and @var{low} is 65535, that is, | |
646 | @ifnottex | |
647 | @w{2**16 - 1.} | |
648 | @end ifnottex | |
649 | @tex | |
650 | @math{2^{16}-1}. | |
651 | @end tex | |
652 | @end defun | |
653 | ||
654 | @c Emacs 19 feature | |
655 | @defun set-visited-file-modtime &optional time | |
656 | This function updates the buffer's record of the last modification time | |
657 | of the visited file, to the value specified by @var{time} if @var{time} | |
658 | is not @code{nil}, and otherwise to the last modification time of the | |
659 | visited file. | |
660 | ||
661 | If @var{time} is neither @code{nil} nor zero, it should have the form | |
662 | @code{(@var{high} . @var{low})} or @code{(@var{high} @var{low})}, in | |
663 | either case containing two integers, each of which holds 16 bits of the | |
664 | time. | |
665 | ||
666 | This function is useful if the buffer was not read from the file | |
667 | normally, or if the file itself has been changed for some known benign | |
668 | reason. | |
669 | @end defun | |
670 | ||
671 | @defun ask-user-about-supersession-threat filename | |
672 | This function is used to ask a user how to proceed after an attempt to | |
673 | modify an buffer visiting file @var{filename} when the file is newer | |
674 | than the buffer text. Emacs detects this because the modification | |
675 | time of the file on disk is newer than the last save-time of the | |
676 | buffer. This means some other program has probably altered the file. | |
677 | ||
678 | @kindex file-supersession | |
679 | Depending on the user's answer, the function may return normally, in | |
680 | which case the modification of the buffer proceeds, or it may signal a | |
681 | @code{file-supersession} error with data @code{(@var{filename})}, in which | |
682 | case the proposed buffer modification is not allowed. | |
683 | ||
684 | This function is called automatically by Emacs on the proper | |
685 | occasions. It exists so you can customize Emacs by redefining it. | |
686 | See the file @file{userlock.el} for the standard definition. | |
687 | ||
688 | See also the file locking mechanism in @ref{File Locks}. | |
689 | @end defun | |
690 | ||
691 | @node Read Only Buffers | |
692 | @section Read-Only Buffers | |
693 | @cindex read-only buffer | |
694 | @cindex buffer, read-only | |
695 | ||
696 | If a buffer is @dfn{read-only}, then you cannot change its contents, | |
697 | although you may change your view of the contents by scrolling and | |
698 | narrowing. | |
699 | ||
700 | Read-only buffers are used in two kinds of situations: | |
701 | ||
702 | @itemize @bullet | |
703 | @item | |
704 | A buffer visiting a write-protected file is normally read-only. | |
705 | ||
706 | Here, the purpose is to inform the user that editing the buffer with the | |
707 | aim of saving it in the file may be futile or undesirable. The user who | |
708 | wants to change the buffer text despite this can do so after clearing | |
709 | the read-only flag with @kbd{C-x C-q}. | |
710 | ||
711 | @item | |
712 | Modes such as Dired and Rmail make buffers read-only when altering the | |
713 | contents with the usual editing commands would probably be a mistake. | |
714 | ||
715 | The special commands of these modes bind @code{buffer-read-only} to | |
716 | @code{nil} (with @code{let}) or bind @code{inhibit-read-only} to | |
717 | @code{t} around the places where they themselves change the text. | |
718 | @end itemize | |
719 | ||
720 | @defvar buffer-read-only | |
721 | This buffer-local variable specifies whether the buffer is read-only. | |
722 | The buffer is read-only if this variable is non-@code{nil}. | |
723 | @end defvar | |
724 | ||
725 | @defvar inhibit-read-only | |
726 | If this variable is non-@code{nil}, then read-only buffers and, | |
727 | depending on the actual value, some or all read-only characters may be | |
728 | modified. Read-only characters in a buffer are those that have | |
729 | non-@code{nil} @code{read-only} properties (either text properties or | |
730 | overlay properties). @xref{Special Properties}, for more information | |
731 | about text properties. @xref{Overlays}, for more information about | |
732 | overlays and their properties. | |
733 | ||
734 | If @code{inhibit-read-only} is @code{t}, all @code{read-only} character | |
735 | properties have no effect. If @code{inhibit-read-only} is a list, then | |
736 | @code{read-only} character properties have no effect if they are members | |
737 | of the list (comparison is done with @code{eq}). | |
738 | @end defvar | |
739 | ||
740 | @deffn Command toggle-read-only &optional arg | |
741 | This command toggles whether the current buffer is read-only. It is | |
742 | intended for interactive use; do not use it in programs. At any given | |
743 | point in a program, you should know whether you want the read-only flag | |
744 | on or off; so you can set @code{buffer-read-only} explicitly to the | |
745 | proper value, @code{t} or @code{nil}. | |
746 | ||
747 | If @var{arg} is non-@code{nil}, it should be a raw prefix argument. | |
748 | @code{toggle-read-only} sets @code{buffer-read-only} to @code{t} if | |
749 | the numeric value of that prefix argument is positive and to | |
750 | @code{nil} otherwise. @xref{Prefix Command Arguments}. | |
751 | @end deffn | |
752 | ||
753 | @defun barf-if-buffer-read-only | |
754 | This function signals a @code{buffer-read-only} error if the current | |
755 | buffer is read-only. @xref{Using Interactive}, for another way to | |
756 | signal an error if the current buffer is read-only. | |
757 | @end defun | |
758 | ||
759 | @node The Buffer List | |
760 | @section The Buffer List | |
761 | @cindex buffer list | |
762 | ||
174dc00c MR |
763 | The @dfn{buffer list} is a list of all live buffers. The order of the |
764 | buffers in this list is based primarily on how recently each buffer has | |
765 | been displayed in a window. Several functions, notably | |
766 | @code{other-buffer}, use this ordering. A buffer list displayed for the | |
767 | user also follows this order. | |
768 | ||
769 | Creating a buffer adds it to the end of the buffer list, and killing a | |
770 | buffer removes it from that list. A buffer moves to the front of this | |
771 | list whenever it is chosen for display in a window (@pxref{Displaying | |
772 | Buffers}) or a window displaying it is selected (@pxref{Selecting | |
773 | Windows}). A buffer moves to the end of the list when it is buried (see | |
774 | @code{bury-buffer}, below). There are no functions available to the | |
775 | Lisp programmer which directly manipulate the buffer list. | |
776 | ||
777 | In addition to the fundamental buffer list just described, Emacs | |
778 | maintains a local buffer list for each frame, in which the buffers that | |
779 | have been displayed (or had their windows selected) in that frame come | |
780 | first. (This order is recorded in the frame's @code{buffer-list} frame | |
781 | parameter; see @ref{Buffer Parameters}.) Buffers never displayed in | |
782 | that frame come afterward, ordered according to the fundamental buffer | |
783 | list. | |
b8d4c8d0 GM |
784 | |
785 | @defun buffer-list &optional frame | |
786 | This function returns the buffer list, including all buffers, even those | |
787 | whose names begin with a space. The elements are actual buffers, not | |
788 | their names. | |
789 | ||
174dc00c MR |
790 | If @var{frame} is a frame, this returns @var{frame}'s local buffer list. |
791 | If @var{frame} is @code{nil} or omitted, the fundamental buffer list is | |
792 | used: the buffers appear in order of most recent display or selection, | |
793 | regardless of which frames they were displayed on. | |
b8d4c8d0 GM |
794 | |
795 | @example | |
796 | @group | |
797 | (buffer-list) | |
798 | @result{} (#<buffer buffers.texi> | |
799 | #<buffer *Minibuf-1*> #<buffer buffer.c> | |
800 | #<buffer *Help*> #<buffer TAGS>) | |
801 | @end group | |
802 | ||
803 | @group | |
804 | ;; @r{Note that the name of the minibuffer} | |
805 | ;; @r{begins with a space!} | |
806 | (mapcar (function buffer-name) (buffer-list)) | |
807 | @result{} ("buffers.texi" " *Minibuf-1*" | |
808 | "buffer.c" "*Help*" "TAGS") | |
809 | @end group | |
810 | @end example | |
811 | @end defun | |
812 | ||
174dc00c MR |
813 | The list returned by @code{buffer-list} is constructed specifically; |
814 | it is not an internal Emacs data structure, and modifying it has no | |
815 | effect on the order of buffers. If you want to change the order of | |
816 | buffers in the fundamental buffer list, here is an easy way: | |
b8d4c8d0 GM |
817 | |
818 | @example | |
819 | (defun reorder-buffer-list (new-list) | |
820 | (while new-list | |
821 | (bury-buffer (car new-list)) | |
822 | (setq new-list (cdr new-list)))) | |
823 | @end example | |
824 | ||
825 | With this method, you can specify any order for the list, but there is | |
826 | no danger of losing a buffer or adding something that is not a valid | |
827 | live buffer. | |
828 | ||
174dc00c MR |
829 | To change the order or value of a specific frame's buffer list, set |
830 | that frame's @code{buffer-list} parameter with | |
831 | @code{modify-frame-parameters} (@pxref{Parameter Access}). | |
b8d4c8d0 GM |
832 | |
833 | @defun other-buffer &optional buffer visible-ok frame | |
834 | This function returns the first buffer in the buffer list other than | |
174dc00c MR |
835 | @var{buffer}. Usually, this is the buffer appearing in the most |
836 | recently selected window (in frame @var{frame} or else the selected | |
837 | frame, @pxref{Input Focus}), aside from @var{buffer}. Buffers whose | |
838 | names start with a space are not considered at all. | |
b8d4c8d0 | 839 | |
174dc00c | 840 | If @var{buffer} is not supplied (or if it is not a live buffer), then |
b8d4c8d0 | 841 | @code{other-buffer} returns the first buffer in the selected frame's |
174dc00c MR |
842 | local buffer list. (If @var{frame} is non-@code{nil}, it returns the |
843 | first buffer in @var{frame}'s local buffer list instead.) | |
b8d4c8d0 GM |
844 | |
845 | If @var{frame} has a non-@code{nil} @code{buffer-predicate} parameter, | |
846 | then @code{other-buffer} uses that predicate to decide which buffers to | |
847 | consider. It calls the predicate once for each buffer, and if the value | |
848 | is @code{nil}, that buffer is ignored. @xref{Buffer Parameters}. | |
849 | ||
850 | @c Emacs 19 feature | |
851 | If @var{visible-ok} is @code{nil}, @code{other-buffer} avoids returning | |
852 | a buffer visible in any window on any visible frame, except as a last | |
174dc00c | 853 | resort. If @var{visible-ok} is non-@code{nil}, then it does not matter |
b8d4c8d0 GM |
854 | whether a buffer is displayed somewhere or not. |
855 | ||
856 | If no suitable buffer exists, the buffer @samp{*scratch*} is returned | |
857 | (and created, if necessary). | |
858 | @end defun | |
859 | ||
174dc00c MR |
860 | @defun last-buffer &optional buffer visible-ok frame |
861 | This function returns the last buffer in @var{frame}'s buffer list other | |
862 | than @var{BUFFER}. If @var{frame} is omitted or @code{nil}, it uses the | |
863 | selected frame's buffer list. | |
864 | ||
865 | The argument @var{visible-ok} is handled as with @code{other-buffer}, | |
866 | see above. If no suitable buffer can be found, the buffer | |
867 | @samp{*scratch*} is returned. | |
868 | @end defun | |
869 | ||
b8d4c8d0 | 870 | @deffn Command bury-buffer &optional buffer-or-name |
174dc00c | 871 | This command puts @var{buffer-or-name} at the end of the buffer list, |
b8d4c8d0 GM |
872 | without changing the order of any of the other buffers on the list. |
873 | This buffer therefore becomes the least desirable candidate for | |
874 | @code{other-buffer} to return. The argument can be either a buffer | |
875 | itself or the name of one. | |
876 | ||
877 | @code{bury-buffer} operates on each frame's @code{buffer-list} parameter | |
174dc00c MR |
878 | as well as the fundamental buffer list; therefore, the buffer that you |
879 | bury will come last in the value of @code{(buffer-list @var{frame})} and | |
880 | in the value of @code{(buffer-list)}. | |
b8d4c8d0 GM |
881 | |
882 | If @var{buffer-or-name} is @code{nil} or omitted, this means to bury the | |
883 | current buffer. In addition, if the buffer is displayed in the selected | |
884 | window, this switches to some other buffer (obtained using | |
174dc00c MR |
885 | @code{other-buffer}) in the selected window. @xref{Displaying Buffers}. |
886 | But if the selected window is dedicated to its buffer, it deletes that | |
887 | window if there are other windows left on its frame. Otherwise, if the | |
888 | selected window is the only window on its frame, it iconifies that | |
889 | frame. If @var{buffer-or-name} is displayed in some other window, it | |
890 | remains displayed there. | |
b8d4c8d0 GM |
891 | |
892 | To replace a buffer in all the windows that display it, use | |
893 | @code{replace-buffer-in-windows}. @xref{Buffers and Windows}. | |
894 | @end deffn | |
895 | ||
174dc00c MR |
896 | @deffn Command unbury-buffer |
897 | This command switches to the last buffer in the local buffer list of the | |
898 | selected frame. More precisely, it calls the function | |
899 | @code{switch-to-buffer} (@pxref{Displaying Buffers}), to display the | |
900 | buffer returned by @code{last-buffer}, see above, in the selected | |
901 | window. | |
902 | @end deffn | |
903 | ||
904 | ||
b8d4c8d0 GM |
905 | @node Creating Buffers |
906 | @section Creating Buffers | |
907 | @cindex creating buffers | |
908 | @cindex buffers, creating | |
909 | ||
910 | This section describes the two primitives for creating buffers. | |
911 | @code{get-buffer-create} creates a buffer if it finds no existing buffer | |
912 | with the specified name; @code{generate-new-buffer} always creates a new | |
913 | buffer and gives it a unique name. | |
914 | ||
915 | Other functions you can use to create buffers include | |
916 | @code{with-output-to-temp-buffer} (@pxref{Temporary Displays}) and | |
917 | @code{create-file-buffer} (@pxref{Visiting Files}). Starting a | |
918 | subprocess can also create a buffer (@pxref{Processes}). | |
919 | ||
4d48fcdc | 920 | @defun get-buffer-create buffer-or-name |
09460d9a MR |
921 | This function returns a buffer named @var{buffer-or-name}. The buffer |
922 | returned does not become the current buffer---this function does not | |
923 | change which buffer is current. | |
924 | ||
925 | @var{buffer-or-name} must be either a string or an existing buffer. If | |
926 | it is a string and a live buffer with that name already exists, | |
927 | @code{get-buffer-create} returns that buffer. If no such buffer exists, | |
928 | it creates a new buffer. If @var{buffer-or-name} is a buffer instead of | |
929 | a string, it is returned as given, even if it is dead. | |
b8d4c8d0 GM |
930 | |
931 | @example | |
932 | @group | |
933 | (get-buffer-create "foo") | |
934 | @result{} #<buffer foo> | |
935 | @end group | |
936 | @end example | |
937 | ||
938 | The major mode for a newly created buffer is set to Fundamental mode. | |
4e3b4528 SM |
939 | (The default value of the variable @code{major-mode} is handled at a higher |
940 | level; see @ref{Auto Major Mode}.) If the name begins with a space, the | |
b8d4c8d0 GM |
941 | buffer initially disables undo information recording (@pxref{Undo}). |
942 | @end defun | |
943 | ||
944 | @defun generate-new-buffer name | |
945 | This function returns a newly created, empty buffer, but does not make | |
946 | it current. If there is no buffer named @var{name}, then that is the | |
947 | name of the new buffer. If that name is in use, this function adds | |
948 | suffixes of the form @samp{<@var{n}>} to @var{name}, where @var{n} is an | |
949 | integer. It tries successive integers starting with 2 until it finds an | |
950 | available name. | |
951 | ||
952 | An error is signaled if @var{name} is not a string. | |
953 | ||
954 | @example | |
955 | @group | |
956 | (generate-new-buffer "bar") | |
957 | @result{} #<buffer bar> | |
958 | @end group | |
959 | @group | |
960 | (generate-new-buffer "bar") | |
961 | @result{} #<buffer bar<2>> | |
962 | @end group | |
963 | @group | |
964 | (generate-new-buffer "bar") | |
965 | @result{} #<buffer bar<3>> | |
966 | @end group | |
967 | @end example | |
968 | ||
4e3b4528 SM |
969 | The major mode for the new buffer is set to Fundamental mode. The default |
970 | value of the variable @code{major-mode} is handled at a higher level. | |
b8d4c8d0 GM |
971 | @xref{Auto Major Mode}. |
972 | ||
973 | See the related function @code{generate-new-buffer-name} in @ref{Buffer | |
974 | Names}. | |
975 | @end defun | |
976 | ||
977 | @node Killing Buffers | |
978 | @section Killing Buffers | |
979 | @cindex killing buffers | |
980 | @cindex buffers, killing | |
981 | ||
982 | @dfn{Killing a buffer} makes its name unknown to Emacs and makes the | |
983 | memory space it occupied available for other use. | |
984 | ||
985 | The buffer object for the buffer that has been killed remains in | |
986 | existence as long as anything refers to it, but it is specially marked | |
987 | so that you cannot make it current or display it. Killed buffers retain | |
988 | their identity, however; if you kill two distinct buffers, they remain | |
989 | distinct according to @code{eq} although both are dead. | |
990 | ||
991 | If you kill a buffer that is current or displayed in a window, Emacs | |
992 | automatically selects or displays some other buffer instead. This means | |
993 | that killing a buffer can in general change the current buffer. | |
994 | Therefore, when you kill a buffer, you should also take the precautions | |
995 | associated with changing the current buffer (unless you happen to know | |
996 | that the buffer being killed isn't current). @xref{Current Buffer}. | |
997 | ||
998 | If you kill a buffer that is the base buffer of one or more indirect | |
999 | buffers, the indirect buffers are automatically killed as well. | |
1000 | ||
1001 | The @code{buffer-name} of a killed buffer is @code{nil}. You can use | |
1002 | this feature to test whether a buffer has been killed: | |
1003 | ||
1004 | @example | |
1005 | @group | |
1006 | (defun buffer-killed-p (buffer) | |
1007 | "Return t if BUFFER is killed." | |
1008 | (not (buffer-name buffer))) | |
1009 | @end group | |
1010 | @end example | |
1011 | ||
f76f8246 | 1012 | @deffn Command kill-buffer &optional buffer-or-name |
b8d4c8d0 GM |
1013 | This function kills the buffer @var{buffer-or-name}, freeing all its |
1014 | memory for other uses or to be returned to the operating system. If | |
f76f8246 MR |
1015 | @var{buffer-or-name} is @code{nil} or omitted, it kills the current |
1016 | buffer. | |
b8d4c8d0 GM |
1017 | |
1018 | Any processes that have this buffer as the @code{process-buffer} are | |
1019 | sent the @code{SIGHUP} signal, which normally causes them to terminate. | |
1020 | (The basic meaning of @code{SIGHUP} is that a dialup line has been | |
1021 | disconnected.) @xref{Signals to Processes}. | |
1022 | ||
1023 | If the buffer is visiting a file and contains unsaved changes, | |
1024 | @code{kill-buffer} asks the user to confirm before the buffer is killed. | |
1025 | It does this even if not called interactively. To prevent the request | |
1026 | for confirmation, clear the modified flag before calling | |
1027 | @code{kill-buffer}. @xref{Buffer Modification}. | |
1028 | ||
02043db0 EZ |
1029 | This function calls @code{replace-buffer-in-windows} for cleaning up |
1030 | all windows currently displaying the buffer to be killed. | |
f76f8246 | 1031 | |
b8d4c8d0 GM |
1032 | Killing a buffer that is already dead has no effect. |
1033 | ||
1034 | This function returns @code{t} if it actually killed the buffer. It | |
1035 | returns @code{nil} if the user refuses to confirm or if | |
1036 | @var{buffer-or-name} was already dead. | |
1037 | ||
1038 | @smallexample | |
1039 | (kill-buffer "foo.unchanged") | |
1040 | @result{} t | |
1041 | (kill-buffer "foo.changed") | |
1042 | ||
1043 | ---------- Buffer: Minibuffer ---------- | |
1044 | Buffer foo.changed modified; kill anyway? (yes or no) @kbd{yes} | |
1045 | ---------- Buffer: Minibuffer ---------- | |
1046 | ||
1047 | @result{} t | |
1048 | @end smallexample | |
1049 | @end deffn | |
1050 | ||
1051 | @defvar kill-buffer-query-functions | |
1052 | After confirming unsaved changes, @code{kill-buffer} calls the functions | |
1053 | in the list @code{kill-buffer-query-functions}, in order of appearance, | |
1054 | with no arguments. The buffer being killed is the current buffer when | |
1055 | they are called. The idea of this feature is that these functions will | |
1056 | ask for confirmation from the user. If any of them returns @code{nil}, | |
1057 | @code{kill-buffer} spares the buffer's life. | |
1058 | @end defvar | |
1059 | ||
1060 | @defvar kill-buffer-hook | |
1061 | This is a normal hook run by @code{kill-buffer} after asking all the | |
1062 | questions it is going to ask, just before actually killing the buffer. | |
1063 | The buffer to be killed is current when the hook functions run. | |
1064 | @xref{Hooks}. This variable is a permanent local, so its local binding | |
1065 | is not cleared by changing major modes. | |
1066 | @end defvar | |
1067 | ||
01f17ae2 | 1068 | @defopt buffer-offer-save |
b8d4c8d0 GM |
1069 | This variable, if non-@code{nil} in a particular buffer, tells |
1070 | @code{save-buffers-kill-emacs} and @code{save-some-buffers} (if the | |
1071 | second optional argument to that function is @code{t}) to offer to | |
1072 | save that buffer, just as they offer to save file-visiting buffers. | |
1073 | @xref{Definition of save-some-buffers}. The variable | |
1074 | @code{buffer-offer-save} automatically becomes buffer-local when set | |
1075 | for any reason. @xref{Buffer-Local Variables}. | |
01f17ae2 | 1076 | @end defopt |
b8d4c8d0 GM |
1077 | |
1078 | @defvar buffer-save-without-query | |
1079 | This variable, if non-@code{nil} in a particular buffer, tells | |
1080 | @code{save-buffers-kill-emacs} and @code{save-some-buffers} to save | |
1081 | this buffer (if it's modified) without asking the user. The variable | |
1082 | automatically becomes buffer-local when set for any reason. | |
1083 | @end defvar | |
1084 | ||
1085 | @defun buffer-live-p object | |
1086 | This function returns @code{t} if @var{object} is a buffer which has | |
1087 | not been killed, @code{nil} otherwise. | |
1088 | @end defun | |
1089 | ||
1090 | @node Indirect Buffers | |
1091 | @section Indirect Buffers | |
1092 | @cindex indirect buffers | |
1093 | @cindex base buffer | |
1094 | ||
1095 | An @dfn{indirect buffer} shares the text of some other buffer, which | |
1096 | is called the @dfn{base buffer} of the indirect buffer. In some ways it | |
1097 | is the analogue, for buffers, of a symbolic link among files. The base | |
1098 | buffer may not itself be an indirect buffer. | |
1099 | ||
1100 | The text of the indirect buffer is always identical to the text of its | |
1101 | base buffer; changes made by editing either one are visible immediately | |
1102 | in the other. This includes the text properties as well as the characters | |
1103 | themselves. | |
1104 | ||
1105 | In all other respects, the indirect buffer and its base buffer are | |
1106 | completely separate. They have different names, independent values of | |
1107 | point, independent narrowing, independent markers and overlays (though | |
1108 | inserting or deleting text in either buffer relocates the markers and | |
1109 | overlays for both), independent major modes, and independent | |
1110 | buffer-local variable bindings. | |
1111 | ||
1112 | An indirect buffer cannot visit a file, but its base buffer can. If | |
1113 | you try to save the indirect buffer, that actually saves the base | |
1114 | buffer. | |
1115 | ||
1116 | Killing an indirect buffer has no effect on its base buffer. Killing | |
1117 | the base buffer effectively kills the indirect buffer in that it cannot | |
1118 | ever again be the current buffer. | |
1119 | ||
1120 | @deffn Command make-indirect-buffer base-buffer name &optional clone | |
1121 | This creates and returns an indirect buffer named @var{name} whose | |
1122 | base buffer is @var{base-buffer}. The argument @var{base-buffer} may | |
1123 | be a live buffer or the name (a string) of an existing buffer. If | |
1124 | @var{name} is the name of an existing buffer, an error is signaled. | |
1125 | ||
1126 | If @var{clone} is non-@code{nil}, then the indirect buffer originally | |
1127 | shares the ``state'' of @var{base-buffer} such as major mode, minor | |
1128 | modes, buffer local variables and so on. If @var{clone} is omitted | |
1129 | or @code{nil} the indirect buffer's state is set to the default state | |
1130 | for new buffers. | |
1131 | ||
1132 | If @var{base-buffer} is an indirect buffer, its base buffer is used as | |
1133 | the base for the new buffer. If, in addition, @var{clone} is | |
1134 | non-@code{nil}, the initial state is copied from the actual base | |
1135 | buffer, not from @var{base-buffer}. | |
1136 | @end deffn | |
1137 | ||
106e6894 | 1138 | @deffn clone-indirect-buffer newname display-flag &optional norecord |
b8d4c8d0 GM |
1139 | This function creates and returns a new indirect buffer that shares |
1140 | the current buffer's base buffer and copies the rest of the current | |
1141 | buffer's attributes. (If the current buffer is not indirect, it is | |
1142 | used as the base buffer.) | |
1143 | ||
1144 | If @var{display-flag} is non-@code{nil}, that means to display the new | |
1145 | buffer by calling @code{pop-to-buffer}. If @var{norecord} is | |
1146 | non-@code{nil}, that means not to put the new buffer to the front of | |
1147 | the buffer list. | |
106e6894 | 1148 | @end deffn |
b8d4c8d0 GM |
1149 | |
1150 | @defun buffer-base-buffer &optional buffer | |
1151 | This function returns the base buffer of @var{buffer}, which defaults | |
1152 | to the current buffer. If @var{buffer} is not indirect, the value is | |
1153 | @code{nil}. Otherwise, the value is another buffer, which is never an | |
1154 | indirect buffer. | |
1155 | @end defun | |
1156 | ||
2aaaf0dd EZ |
1157 | @node Swapping Text |
1158 | @section Swapping Text Between Two Buffers | |
1159 | @cindex swap text between buffers | |
1160 | @cindex virtual buffers | |
1161 | ||
1162 | Specialized modes sometimes need to let the user access from the | |
1163 | same buffer several vastly different types of text. For example, you | |
1164 | may need to display a summary of the buffer text, in addition to | |
1165 | letting the user access the text itself. | |
1166 | ||
1167 | This could be implemented with multiple buffers (kept in sync when | |
1168 | the user edits the text), or with narrowing (@pxref{Narrowing}). But | |
1169 | these alternatives might sometimes become tedious or prohibitively | |
1170 | expensive, especially if each type of text requires expensive | |
1171 | buffer-global operations in order to provide correct display and | |
1172 | editing commands. | |
1173 | ||
1174 | Emacs provides another facility for such modes: you can quickly swap | |
1175 | buffer text between two buffers with @code{buffer-swap-text}. This | |
1176 | function is very fast because it doesn't move any text, it only | |
1177 | changes the internal data structures of the buffer object to point to | |
1178 | a different chunk of text. Using it, you can pretend that a group of | |
1179 | two or more buffers are actually a single virtual buffer that holds | |
1180 | the contents of all the individual buffers together. | |
1181 | ||
1182 | @defun buffer-swap-text buffer | |
1183 | This function swaps text between the current buffer and its argument | |
1184 | @var{buffer}. It signals an error if one of the two buffers is an | |
1185 | indirect buffer (@pxref{Indirect Buffers}) or is a base buffer of an | |
1186 | indirect buffer. | |
1187 | ||
1188 | All the buffer properties that are related to the buffer text are | |
1189 | swapped as well: the positions of point and mark, all the markers, the | |
1190 | overlays, the text properties, the undo list, the value of the | |
1191 | @code{enable-multibyte-characters} flag (@pxref{Text Representations, | |
1192 | enable-multibyte-characters}), etc. | |
1193 | @end defun | |
1194 | ||
137987ab RS |
1195 | If you use @code{buffer-swap-text} on a file-visiting buffer, you |
1196 | should set up a hook to save the buffer's original text rather than | |
1197 | what it was swapped with. @code{write-region-annotate-functions} | |
1198 | works for this purpose. You should probably set | |
1199 | @code{buffer-saved-size} to @minus{}2 in the buffer, so that changes | |
1200 | in the text it is swapped with will not interfere with auto-saving. | |
1201 | ||
b8d4c8d0 GM |
1202 | @node Buffer Gap |
1203 | @section The Buffer Gap | |
1204 | ||
1205 | Emacs buffers are implemented using an invisible @dfn{gap} to make | |
1206 | insertion and deletion faster. Insertion works by filling in part of | |
1207 | the gap, and deletion adds to the gap. Of course, this means that the | |
1208 | gap must first be moved to the locus of the insertion or deletion. | |
1209 | Emacs moves the gap only when you try to insert or delete. This is why | |
1210 | your first editing command in one part of a large buffer, after | |
1211 | previously editing in another far-away part, sometimes involves a | |
1212 | noticeable delay. | |
1213 | ||
1214 | This mechanism works invisibly, and Lisp code should never be affected | |
1215 | by the gap's current location, but these functions are available for | |
1216 | getting information about the gap status. | |
1217 | ||
1218 | @defun gap-position | |
1219 | This function returns the current gap position in the current buffer. | |
1220 | @end defun | |
1221 | ||
1222 | @defun gap-size | |
1223 | This function returns the current gap size of the current buffer. | |
1224 | @end defun | |
1225 | ||
1226 | @ignore | |
1227 | arch-tag: 2e53cfab-5691-41f6-b5a8-9c6a3462399c | |
1228 | @end ignore |