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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
651f374c | 3 | @c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999, 2000, 2001, |
4e6835db | 4 | @c 2002, 2003, 2004, 2005, 2006, 2007 Free Software Foundation, Inc. |
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5 | @c See the file elisp.texi for copying conditions. |
6 | @setfilename ../info/positions | |
7 | @node Positions, Markers, Frames, Top | |
8 | @chapter Positions | |
9 | @cindex position (in buffer) | |
10 | ||
29679a81 | 11 | A @dfn{position} is the index of a character in the text of a buffer. |
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12 | More precisely, a position identifies the place between two characters |
13 | (or before the first character, or after the last character), so we can | |
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14 | speak of the character before or after a given position. However, we |
15 | often speak of the character ``at'' a position, meaning the character | |
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16 | after that position. |
17 | ||
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18 | Positions are usually represented as integers starting from 1, but |
19 | can also be represented as @dfn{markers}---special objects that | |
20 | relocate automatically when text is inserted or deleted so they stay | |
21 | with the surrounding characters. Functions that expect an argument to | |
22 | be a position (an integer), but accept a marker as a substitute, | |
23 | normally ignore which buffer the marker points into; they convert the | |
24 | marker to an integer, and use that integer, exactly as if you had | |
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25 | passed the integer as the argument, even if the marker points to the |
26 | ``wrong'' buffer. A marker that points nowhere cannot convert to an | |
27 | integer; using it instead of an integer causes an error. | |
28 | @xref{Markers}. | |
7015aca4 | 29 | |
2468d0c0 | 30 | See also the ``field'' feature (@pxref{Fields}), which provides |
a39c2e0d | 31 | functions that are used by many cursor-motion commands. |
2468d0c0 | 32 | |
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33 | @menu |
34 | * Point:: The special position where editing takes place. | |
35 | * Motion:: Changing point. | |
36 | * Excursions:: Temporary motion and buffer changes. | |
37 | * Narrowing:: Restricting editing to a portion of the buffer. | |
38 | @end menu | |
39 | ||
40 | @node Point | |
41 | @section Point | |
42 | @cindex point | |
43 | ||
44 | @dfn{Point} is a special buffer position used by many editing | |
45 | commands, including the self-inserting typed characters and text | |
46 | insertion functions. Other commands move point through the text | |
47 | to allow editing and insertion at different places. | |
48 | ||
49 | Like other positions, point designates a place between two characters | |
50 | (or before the first character, or after the last character), rather | |
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51 | than a particular character. Usually terminals display the cursor over |
52 | the character that immediately follows point; point is actually before | |
53 | the character on which the cursor sits. | |
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54 | |
55 | @cindex point with narrowing | |
8241495d RS |
56 | The value of point is a number no less than 1, and no greater than the |
57 | buffer size plus 1. If narrowing is in effect (@pxref{Narrowing}), then | |
58 | point is constrained to fall within the accessible portion of the buffer | |
59 | (possibly at one end of it). | |
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60 | |
61 | Each buffer has its own value of point, which is independent of the | |
62 | value of point in other buffers. Each window also has a value of point, | |
63 | which is independent of the value of point in other windows on the same | |
64 | buffer. This is why point can have different values in various windows | |
65 | that display the same buffer. When a buffer appears in only one window, | |
66 | the buffer's point and the window's point normally have the same value, | |
67 | so the distinction is rarely important. @xref{Window Point}, for more | |
68 | details. | |
69 | ||
70 | @defun point | |
71 | @cindex current buffer position | |
29679a81 | 72 | This function returns the value of point in the current buffer, |
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73 | as an integer. |
74 | ||
75 | @need 700 | |
76 | @example | |
77 | @group | |
78 | (point) | |
79 | @result{} 175 | |
80 | @end group | |
81 | @end example | |
82 | @end defun | |
83 | ||
84 | @defun point-min | |
29679a81 RS |
85 | This function returns the minimum accessible value of point in the |
86 | current buffer. This is normally 1, but if narrowing is in effect, it | |
87 | is the position of the start of the region that you narrowed to. | |
88 | (@xref{Narrowing}.) | |
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89 | @end defun |
90 | ||
91 | @defun point-max | |
29679a81 | 92 | This function returns the maximum accessible value of point in the |
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93 | current buffer. This is @code{(1+ (buffer-size))}, unless narrowing is |
94 | in effect, in which case it is the position of the end of the region | |
8241495d | 95 | that you narrowed to. (@xref{Narrowing}.) |
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96 | @end defun |
97 | ||
98 | @defun buffer-end flag | |
bf4fb025 LT |
99 | This function returns @code{(point-max)} if @var{flag} is greater than |
100 | 0, @code{(point-min)} otherwise. The argument @var{flag} must be a | |
101 | number. | |
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102 | @end defun |
103 | ||
8241495d | 104 | @defun buffer-size &optional buffer |
29679a81 | 105 | This function returns the total number of characters in the current |
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106 | buffer. In the absence of any narrowing (@pxref{Narrowing}), |
107 | @code{point-max} returns a value one larger than this. | |
108 | ||
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109 | If you specify a buffer, @var{buffer}, then the value is the |
110 | size of @var{buffer}. | |
111 | ||
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112 | @example |
113 | @group | |
114 | (buffer-size) | |
115 | @result{} 35 | |
116 | @end group | |
117 | @group | |
118 | (point-max) | |
119 | @result{} 36 | |
120 | @end group | |
121 | @end example | |
122 | @end defun | |
123 | ||
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124 | @node Motion |
125 | @section Motion | |
126 | ||
127 | Motion functions change the value of point, either relative to the | |
128 | current value of point, relative to the beginning or end of the buffer, | |
129 | or relative to the edges of the selected window. @xref{Point}. | |
130 | ||
131 | @menu | |
132 | * Character Motion:: Moving in terms of characters. | |
133 | * Word Motion:: Moving in terms of words. | |
134 | * Buffer End Motion:: Moving to the beginning or end of the buffer. | |
135 | * Text Lines:: Moving in terms of lines of text. | |
136 | * Screen Lines:: Moving in terms of lines as displayed. | |
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137 | * List Motion:: Moving by parsing lists and sexps. |
138 | * Skipping Characters:: Skipping characters belonging to a certain set. | |
139 | @end menu | |
140 | ||
141 | @node Character Motion | |
142 | @subsection Motion by Characters | |
143 | ||
144 | These functions move point based on a count of characters. | |
29679a81 | 145 | @code{goto-char} is the fundamental primitive; the other functions use |
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146 | that. |
147 | ||
148 | @deffn Command goto-char position | |
149 | This function sets point in the current buffer to the value | |
150 | @var{position}. If @var{position} is less than 1, it moves point to the | |
151 | beginning of the buffer. If @var{position} is greater than the length | |
152 | of the buffer, it moves point to the end. | |
153 | ||
154 | If narrowing is in effect, @var{position} still counts from the | |
155 | beginning of the buffer, but point cannot go outside the accessible | |
156 | portion. If @var{position} is out of range, @code{goto-char} moves | |
157 | point to the beginning or the end of the accessible portion. | |
158 | ||
159 | When this function is called interactively, @var{position} is the | |
160 | numeric prefix argument, if provided; otherwise it is read from the | |
161 | minibuffer. | |
162 | ||
163 | @code{goto-char} returns @var{position}. | |
164 | @end deffn | |
165 | ||
166 | @deffn Command forward-char &optional count | |
167 | @c @kindex beginning-of-buffer | |
168 | @c @kindex end-of-buffer | |
169 | This function moves point @var{count} characters forward, towards the | |
170 | end of the buffer (or backward, towards the beginning of the buffer, if | |
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171 | @var{count} is negative). If @var{count} is @code{nil}, the default |
172 | is 1. | |
173 | ||
174 | If this attempts to move past the beginning or end of the buffer (or | |
175 | the limits of the accessible portion, when narrowing is in effect), it | |
176 | signals an error with error symbol @code{beginning-of-buffer} or | |
177 | @code{end-of-buffer}. | |
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178 | |
179 | In an interactive call, @var{count} is the numeric prefix argument. | |
180 | @end deffn | |
181 | ||
182 | @deffn Command backward-char &optional count | |
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183 | This is just like @code{forward-char} except that it moves |
184 | in the opposite direction. | |
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185 | @end deffn |
186 | ||
187 | @node Word Motion | |
188 | @subsection Motion by Words | |
189 | ||
190 | These functions for parsing words use the syntax table to decide | |
191 | whether a given character is part of a word. @xref{Syntax Tables}. | |
192 | ||
033a0350 | 193 | @deffn Command forward-word &optional count |
7015aca4 | 194 | This function moves point forward @var{count} words (or backward if |
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195 | @var{count} is negative). If @var{count} is @code{nil}, it moves |
196 | forward one word. | |
197 | ||
198 | ``Moving one word'' means moving until point crosses a | |
199 | word-constituent character and then encounters a word-separator | |
200 | character. However, this function cannot move point past the boundary | |
201 | of the accessible portion of the buffer, or across a field boundary | |
202 | (@pxref{Fields}). The most common case of a field boundary is the end | |
203 | of the prompt in the minibuffer. | |
7015aca4 | 204 | |
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205 | If it is possible to move @var{count} words, without being stopped |
206 | prematurely by the buffer boundary or a field boundary, the value is | |
207 | @code{t}. Otherwise, the return value is @code{nil} and point stops at | |
208 | the buffer boundary or field boundary. | |
8241495d | 209 | |
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210 | If @code{inhibit-field-text-motion} is non-@code{nil}, |
211 | this function ignores field boundaries. | |
212 | ||
2468d0c0 | 213 | In an interactive call, @var{count} is specified by the numeric prefix |
033a0350 | 214 | argument. If @var{count} is omitted or @code{nil}, it defaults to 1. |
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215 | @end deffn |
216 | ||
033a0350 | 217 | @deffn Command backward-word &optional count |
29679a81 | 218 | This function is just like @code{forward-word}, except that it moves |
7015aca4 | 219 | backward until encountering the front of a word, rather than forward. |
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220 | @end deffn |
221 | ||
222 | @defvar words-include-escapes | |
223 | @c Emacs 19 feature | |
224 | This variable affects the behavior of @code{forward-word} and everything | |
225 | that uses it. If it is non-@code{nil}, then characters in the | |
226 | ``escape'' and ``character quote'' syntax classes count as part of | |
227 | words. Otherwise, they do not. | |
228 | @end defvar | |
229 | ||
72821190 | 230 | @defvar inhibit-field-text-motion |
72821190 RS |
231 | If this variable is non-@code{nil}, certain motion functions including |
232 | @code{forward-word}, @code{forward-sentence}, and | |
37680279 | 233 | @code{forward-paragraph} ignore field boundaries. |
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234 | @end defvar |
235 | ||
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236 | @node Buffer End Motion |
237 | @subsection Motion to an End of the Buffer | |
238 | ||
239 | To move point to the beginning of the buffer, write: | |
240 | ||
241 | @example | |
242 | @group | |
243 | (goto-char (point-min)) | |
244 | @end group | |
245 | @end example | |
246 | ||
247 | @noindent | |
248 | Likewise, to move to the end of the buffer, use: | |
249 | ||
250 | @example | |
251 | @group | |
252 | (goto-char (point-max)) | |
253 | @end group | |
254 | @end example | |
255 | ||
29679a81 | 256 | Here are two commands that users use to do these things. They are |
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257 | documented here to warn you not to use them in Lisp programs, because |
258 | they set the mark and display messages in the echo area. | |
259 | ||
260 | @deffn Command beginning-of-buffer &optional n | |
261 | This function moves point to the beginning of the buffer (or the limits | |
262 | of the accessible portion, when narrowing is in effect), setting the | |
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263 | mark at the previous position (except in Transient Mark mode, if |
264 | the mark is already active, it does not set the mark.) | |
7015aca4 | 265 | |
938183e5 RS |
266 | If @var{n} is non-@code{nil}, then it puts point @var{n} tenths of the |
267 | way from the beginning of the accessible portion of the buffer. In an | |
268 | interactive call, @var{n} is the numeric prefix argument, if provided; | |
269 | otherwise @var{n} defaults to @code{nil}. | |
7015aca4 | 270 | |
969fe9b5 | 271 | @strong{Warning:} Don't use this function in Lisp programs! |
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272 | @end deffn |
273 | ||
274 | @deffn Command end-of-buffer &optional n | |
938183e5 RS |
275 | This function moves point to the end of the buffer (or the limits of |
276 | the accessible portion, when narrowing is in effect), setting the mark | |
277 | at the previous position (except in Transient Mark mode when the mark | |
278 | is already active). If @var{n} is non-@code{nil}, then it puts point | |
279 | @var{n} tenths of the way from the end of the accessible portion of | |
280 | the buffer. | |
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281 | |
282 | In an interactive call, @var{n} is the numeric prefix argument, | |
283 | if provided; otherwise @var{n} defaults to @code{nil}. | |
284 | ||
969fe9b5 | 285 | @strong{Warning:} Don't use this function in Lisp programs! |
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286 | @end deffn |
287 | ||
288 | @node Text Lines | |
289 | @subsection Motion by Text Lines | |
290 | @cindex lines | |
291 | ||
292 | Text lines are portions of the buffer delimited by newline characters, | |
293 | which are regarded as part of the previous line. The first text line | |
294 | begins at the beginning of the buffer, and the last text line ends at | |
295 | the end of the buffer whether or not the last character is a newline. | |
296 | The division of the buffer into text lines is not affected by the width | |
297 | of the window, by line continuation in display, or by how tabs and | |
298 | control characters are displayed. | |
299 | ||
300 | @deffn Command goto-line line | |
301 | This function moves point to the front of the @var{line}th line, | |
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302 | counting from line 1 at beginning of the buffer. If @var{line} is less |
303 | than 1, it moves point to the beginning of the buffer. If @var{line} is | |
7015aca4 | 304 | greater than the number of lines in the buffer, it moves point to the |
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305 | end of the buffer---that is, the @emph{end of the last line} of the |
306 | buffer. This is the only case in which @code{goto-line} does not | |
307 | necessarily move to the beginning of a line. | |
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308 | |
309 | If narrowing is in effect, then @var{line} still counts from the | |
310 | beginning of the buffer, but point cannot go outside the accessible | |
311 | portion. So @code{goto-line} moves point to the beginning or end of the | |
312 | accessible portion, if the line number specifies an inaccessible | |
313 | position. | |
314 | ||
315 | The return value of @code{goto-line} is the difference between | |
316 | @var{line} and the line number of the line to which point actually was | |
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317 | able to move (in the full buffer, before taking account of narrowing). |
318 | Thus, the value is positive if the scan encounters the real end of the | |
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319 | buffer before finding the specified line. The value is zero if scan |
320 | encounters the end of the accessible portion but not the real end of the | |
321 | buffer. | |
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322 | |
323 | In an interactive call, @var{line} is the numeric prefix argument if | |
324 | one has been provided. Otherwise @var{line} is read in the minibuffer. | |
325 | @end deffn | |
326 | ||
327 | @deffn Command beginning-of-line &optional count | |
328 | This function moves point to the beginning of the current line. With an | |
329 | argument @var{count} not @code{nil} or 1, it moves forward | |
330 | @var{count}@minus{}1 lines and then to the beginning of the line. | |
331 | ||
1977bbf4 | 332 | This function does not move point across a field boundary |
2751e4a0 | 333 | (@pxref{Fields}) unless doing so would move beyond there to a |
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334 | different line; therefore, if @var{count} is @code{nil} or 1, and |
335 | point starts at a field boundary, point does not move. To ignore | |
336 | field boundaries, either bind @code{inhibit-field-text-motion} to | |
337 | @code{t}, or use the @code{forward-line} function instead. For | |
338 | instance, @code{(forward-line 0)} does the same thing as | |
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339 | @code{(beginning-of-line)}, except that it ignores field boundaries. |
340 | ||
7015aca4 | 341 | If this function reaches the end of the buffer (or of the accessible |
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342 | portion, if narrowing is in effect), it positions point there. No error |
343 | is signaled. | |
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344 | @end deffn |
345 | ||
2616f553 | 346 | @defun line-beginning-position &optional count |
2616f553 KH |
347 | Return the position that @code{(beginning-of-line @var{count})} |
348 | would move to. | |
349 | @end defun | |
350 | ||
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351 | @deffn Command end-of-line &optional count |
352 | This function moves point to the end of the current line. With an | |
353 | argument @var{count} not @code{nil} or 1, it moves forward | |
354 | @var{count}@minus{}1 lines and then to the end of the line. | |
355 | ||
1977bbf4 | 356 | This function does not move point across a field boundary |
2751e4a0 | 357 | (@pxref{Fields}) unless doing so would move beyond there to a |
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358 | different line; therefore, if @var{count} is @code{nil} or 1, and |
359 | point starts at a field boundary, point does not move. To ignore | |
360 | field boundaries, bind @code{inhibit-field-text-motion} to @code{t}. | |
2751e4a0 | 361 | |
7015aca4 | 362 | If this function reaches the end of the buffer (or of the accessible |
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363 | portion, if narrowing is in effect), it positions point there. No error |
364 | is signaled. | |
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365 | @end deffn |
366 | ||
2616f553 | 367 | @defun line-end-position &optional count |
2616f553 KH |
368 | Return the position that @code{(end-of-line @var{count})} |
369 | would move to. | |
370 | @end defun | |
371 | ||
7015aca4 RS |
372 | @deffn Command forward-line &optional count |
373 | @cindex beginning of line | |
374 | This function moves point forward @var{count} lines, to the beginning of | |
375 | the line. If @var{count} is negative, it moves point | |
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376 | @minus{}@var{count} lines backward, to the beginning of a line. If |
377 | @var{count} is zero, it moves point to the beginning of the current | |
938183e5 | 378 | line. If @var{count} is @code{nil}, that means 1. |
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379 | |
380 | If @code{forward-line} encounters the beginning or end of the buffer (or | |
381 | of the accessible portion) before finding that many lines, it sets point | |
382 | there. No error is signaled. | |
383 | ||
384 | @code{forward-line} returns the difference between @var{count} and the | |
385 | number of lines actually moved. If you attempt to move down five lines | |
386 | from the beginning of a buffer that has only three lines, point stops at | |
387 | the end of the last line, and the value will be 2. | |
388 | ||
389 | In an interactive call, @var{count} is the numeric prefix argument. | |
390 | @end deffn | |
391 | ||
392 | @defun count-lines start end | |
393 | @cindex lines in region | |
5148bc3c | 394 | @anchor{Definition of count-lines} |
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395 | This function returns the number of lines between the positions |
396 | @var{start} and @var{end} in the current buffer. If @var{start} and | |
397 | @var{end} are equal, then it returns 0. Otherwise it returns at least | |
398 | 1, even if @var{start} and @var{end} are on the same line. This is | |
399 | because the text between them, considered in isolation, must contain at | |
400 | least one line unless it is empty. | |
401 | ||
402 | Here is an example of using @code{count-lines}: | |
403 | ||
404 | @example | |
405 | @group | |
406 | (defun current-line () | |
407 | "Return the vertical position of point@dots{}" | |
408 | (+ (count-lines (window-start) (point)) | |
360f2e91 | 409 | (if (= (current-column) 0) 1 0))) |
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410 | @end group |
411 | @end example | |
412 | @end defun | |
413 | ||
3faa99ca KS |
414 | @defun line-number-at-pos &optional pos |
415 | @cindex line number | |
416 | This function returns the line number in the current buffer | |
7fdc81ab | 417 | corresponding to the buffer position @var{pos}. If @var{pos} is @code{nil} |
00991494 | 418 | or omitted, the current buffer position is used. |
1cb60b5a | 419 | @end defun |
3faa99ca | 420 | |
7015aca4 RS |
421 | @ignore |
422 | @c ================ | |
423 | The @code{previous-line} and @code{next-line} commands are functions | |
424 | that should not be used in programs. They are for users and are | |
425 | mentioned here only for completeness. | |
426 | ||
427 | @deffn Command previous-line count | |
428 | @cindex goal column | |
429 | This function moves point up @var{count} lines (down if @var{count} | |
430 | is negative). In moving, it attempts to keep point in the ``goal column'' | |
431 | (normally the same column that it was at the beginning of the move). | |
432 | ||
433 | If there is no character in the target line exactly under the current | |
434 | column, point is positioned after the character in that line which | |
435 | spans this column, or at the end of the line if it is not long enough. | |
436 | ||
437 | If it attempts to move beyond the top or bottom of the buffer (or clipped | |
438 | region), then point is positioned in the goal column in the top or | |
439 | bottom line. No error is signaled. | |
440 | ||
441 | In an interactive call, @var{count} will be the numeric | |
442 | prefix argument. | |
443 | ||
444 | The command @code{set-goal-column} can be used to create a semipermanent | |
445 | goal column to which this command always moves. Then it does not try to | |
446 | move vertically. | |
447 | ||
448 | If you are thinking of using this in a Lisp program, consider using | |
449 | @code{forward-line} with a negative argument instead. It is usually easier | |
450 | to use and more reliable (no dependence on goal column, etc.). | |
451 | @end deffn | |
452 | ||
453 | @deffn Command next-line count | |
454 | This function moves point down @var{count} lines (up if @var{count} | |
455 | is negative). In moving, it attempts to keep point in the ``goal column'' | |
456 | (normally the same column that it was at the beginning of the move). | |
457 | ||
458 | If there is no character in the target line exactly under the current | |
459 | column, point is positioned after the character in that line which | |
460 | spans this column, or at the end of the line if it is not long enough. | |
461 | ||
462 | If it attempts to move beyond the top or bottom of the buffer (or clipped | |
463 | region), then point is positioned in the goal column in the top or | |
464 | bottom line. No error is signaled. | |
465 | ||
466 | In the case where the @var{count} is 1, and point is on the last | |
467 | line of the buffer (or clipped region), a new empty line is inserted at the | |
468 | end of the buffer (or clipped region) and point moved there. | |
469 | ||
470 | In an interactive call, @var{count} will be the numeric | |
471 | prefix argument. | |
472 | ||
473 | The command @code{set-goal-column} can be used to create a semipermanent | |
474 | goal column to which this command always moves. Then it does not try to | |
475 | move vertically. | |
476 | ||
477 | If you are thinking of using this in a Lisp program, consider using | |
478 | @code{forward-line} instead. It is usually easier | |
479 | to use and more reliable (no dependence on goal column, etc.). | |
480 | @end deffn | |
481 | ||
482 | @c ================ | |
483 | @end ignore | |
484 | ||
485 | Also see the functions @code{bolp} and @code{eolp} in @ref{Near Point}. | |
486 | These functions do not move point, but test whether it is already at the | |
487 | beginning or end of a line. | |
488 | ||
489 | @node Screen Lines | |
490 | @subsection Motion by Screen Lines | |
491 | ||
492 | The line functions in the previous section count text lines, delimited | |
493 | only by newline characters. By contrast, these functions count screen | |
494 | lines, which are defined by the way the text appears on the screen. A | |
495 | text line is a single screen line if it is short enough to fit the width | |
496 | of the selected window, but otherwise it may occupy several screen | |
497 | lines. | |
498 | ||
499 | In some cases, text lines are truncated on the screen rather than | |
500 | continued onto additional screen lines. In these cases, | |
501 | @code{vertical-motion} moves point much like @code{forward-line}. | |
502 | @xref{Truncation}. | |
503 | ||
29679a81 | 504 | Because the width of a given string depends on the flags that control |
7015aca4 RS |
505 | the appearance of certain characters, @code{vertical-motion} behaves |
506 | differently, for a given piece of text, depending on the buffer it is | |
507 | in, and even on the selected window (because the width, the truncation | |
508 | flag, and display table may vary between windows). @xref{Usual | |
509 | Display}. | |
510 | ||
788583a1 JB |
511 | These functions scan text to determine where screen lines break, and |
512 | thus take time proportional to the distance scanned. If you intend to | |
513 | use them heavily, Emacs provides caches which may improve the | |
a9f0a989 | 514 | performance of your code. @xref{Truncation, cache-long-line-scans}. |
788583a1 | 515 | |
a890e1b0 | 516 | @defun vertical-motion count &optional window |
7015aca4 RS |
517 | This function moves point to the start of the screen line @var{count} |
518 | screen lines down from the screen line containing point. If @var{count} | |
519 | is negative, it moves up instead. | |
520 | ||
f9f59935 RS |
521 | @code{vertical-motion} returns the number of screen lines over which it |
522 | moved point. The value may be less in absolute value than @var{count} | |
523 | if the beginning or end of the buffer was reached. | |
a890e1b0 RS |
524 | |
525 | The window @var{window} is used for obtaining parameters such as the | |
526 | width, the horizontal scrolling, and the display table. But | |
527 | @code{vertical-motion} always operates on the current buffer, even if | |
528 | @var{window} currently displays some other buffer. | |
7015aca4 RS |
529 | @end defun |
530 | ||
f4f65a42 RS |
531 | @defun count-screen-lines &optional beg end count-final-newline window |
532 | This function returns the number of screen lines in the text from | |
533 | @var{beg} to @var{end}. The number of screen lines may be different | |
534 | from the number of actual lines, due to line continuation, the display | |
535 | table, etc. If @var{beg} and @var{end} are @code{nil} or omitted, | |
536 | they default to the beginning and end of the accessible portion of the | |
537 | buffer. | |
538 | ||
539 | If the region ends with a newline, that is ignored unless the optional | |
540 | third argument @var{count-final-newline} is non-@code{nil}. | |
541 | ||
542 | The optional fourth argument @var{window} specifies the window for | |
543 | obtaining parameters such as width, horizontal scrolling, and so on. | |
544 | The default is to use the selected window's parameters. | |
545 | ||
546 | Like @code{vertical-motion}, @code{count-screen-lines} always uses the | |
547 | current buffer, regardless of which buffer is displayed in | |
548 | @var{window}. This makes possible to use @code{count-screen-lines} in | |
549 | any buffer, whether or not it is currently displayed in some window. | |
550 | @end defun | |
551 | ||
7015aca4 RS |
552 | @deffn Command move-to-window-line count |
553 | This function moves point with respect to the text currently displayed | |
554 | in the selected window. It moves point to the beginning of the screen | |
555 | line @var{count} screen lines from the top of the window. If | |
556 | @var{count} is negative, that specifies a position | |
29679a81 RS |
557 | @w{@minus{}@var{count}} lines from the bottom (or the last line of the |
558 | buffer, if the buffer ends above the specified screen position). | |
7015aca4 RS |
559 | |
560 | If @var{count} is @code{nil}, then point moves to the beginning of the | |
561 | line in the middle of the window. If the absolute value of @var{count} | |
562 | is greater than the size of the window, then point moves to the place | |
29679a81 | 563 | that would appear on that screen line if the window were tall enough. |
7015aca4 RS |
564 | This will probably cause the next redisplay to scroll to bring that |
565 | location onto the screen. | |
566 | ||
567 | In an interactive call, @var{count} is the numeric prefix argument. | |
568 | ||
29679a81 RS |
569 | The value returned is the window line number point has moved to, with |
570 | the top line in the window numbered 0. | |
7015aca4 RS |
571 | @end deffn |
572 | ||
a890e1b0 | 573 | @defun compute-motion from frompos to topos width offsets window |
29679a81 RS |
574 | This function scans the current buffer, calculating screen positions. |
575 | It scans the buffer forward from position @var{from}, assuming that is | |
576 | at screen coordinates @var{frompos}, to position @var{to} or coordinates | |
577 | @var{topos}, whichever comes first. It returns the ending buffer | |
578 | position and screen coordinates. | |
7015aca4 RS |
579 | |
580 | The coordinate arguments @var{frompos} and @var{topos} are cons cells of | |
581 | the form @code{(@var{hpos} . @var{vpos})}. | |
582 | ||
583 | The argument @var{width} is the number of columns available to display | |
c7c63bf7 RS |
584 | text; this affects handling of continuation lines. @code{nil} means |
585 | the actual number of usable text columns in the window, which is | |
586 | equivalent to the value returned by @code{(window-width window)}. | |
7015aca4 RS |
587 | |
588 | The argument @var{offsets} is either @code{nil} or a cons cell of the | |
589 | form @code{(@var{hscroll} . @var{tab-offset})}. Here @var{hscroll} is | |
a890e1b0 | 590 | the number of columns not being displayed at the left margin; most |
a9f0a989 | 591 | callers get this by calling @code{window-hscroll}. Meanwhile, |
a890e1b0 RS |
592 | @var{tab-offset} is the offset between column numbers on the screen and |
593 | column numbers in the buffer. This can be nonzero in a continuation | |
594 | line, when the previous screen lines' widths do not add up to a multiple | |
595 | of @code{tab-width}. It is always zero in a non-continuation line. | |
596 | ||
29679a81 RS |
597 | The window @var{window} serves only to specify which display table to |
598 | use. @code{compute-motion} always operates on the current buffer, | |
599 | regardless of what buffer is displayed in @var{window}. | |
7015aca4 RS |
600 | |
601 | The return value is a list of five elements: | |
602 | ||
603 | @example | |
fa166242 | 604 | (@var{pos} @var{hpos} @var{vpos} @var{prevhpos} @var{contin}) |
7015aca4 RS |
605 | @end example |
606 | ||
607 | @noindent | |
608 | Here @var{pos} is the buffer position where the scan stopped, @var{vpos} | |
29679a81 RS |
609 | is the vertical screen position, and @var{hpos} is the horizontal screen |
610 | position. | |
7015aca4 RS |
611 | |
612 | The result @var{prevhpos} is the horizontal position one character back | |
29679a81 RS |
613 | from @var{pos}. The result @var{contin} is @code{t} if the last line |
614 | was continued after (or within) the previous character. | |
7015aca4 | 615 | |
f9f59935 | 616 | For example, to find the buffer position of column @var{col} of screen line |
7015aca4 RS |
617 | @var{line} of a certain window, pass the window's display start location |
618 | as @var{from} and the window's upper-left coordinates as @var{frompos}. | |
619 | Pass the buffer's @code{(point-max)} as @var{to}, to limit the scan to | |
29679a81 | 620 | the end of the accessible portion of the buffer, and pass @var{line} and |
7015aca4 RS |
621 | @var{col} as @var{topos}. Here's a function that does this: |
622 | ||
623 | @example | |
624 | (defun coordinates-of-position (col line) | |
625 | (car (compute-motion (window-start) | |
626 | '(0 . 0) | |
29679a81 | 627 | (point-max) |
7015aca4 RS |
628 | (cons col line) |
629 | (window-width) | |
29679a81 RS |
630 | (cons (window-hscroll) 0) |
631 | (selected-window)))) | |
7015aca4 | 632 | @end example |
a890e1b0 RS |
633 | |
634 | When you use @code{compute-motion} for the minibuffer, you need to use | |
635 | @code{minibuffer-prompt-width} to get the horizontal position of the | |
0a54f38c | 636 | beginning of the first screen line. @xref{Minibuffer Contents}. |
7015aca4 RS |
637 | @end defun |
638 | ||
7015aca4 RS |
639 | @node List Motion |
640 | @comment node-name, next, previous, up | |
177c0ea7 | 641 | @subsection Moving over Balanced Expressions |
7015aca4 RS |
642 | @cindex sexp motion |
643 | @cindex Lisp expression motion | |
644 | @cindex list motion | |
645 | ||
646 | Here are several functions concerned with balanced-parenthesis | |
647 | expressions (also called @dfn{sexps} in connection with moving across | |
648 | them in Emacs). The syntax table controls how these functions interpret | |
649 | various characters; see @ref{Syntax Tables}. @xref{Parsing | |
650 | Expressions}, for lower-level primitives for scanning sexps or parts of | |
333c5fc5 JB |
651 | sexps. For user-level commands, see @ref{Parentheses,, Commands for |
652 | Editing with Parentheses, emacs, The GNU Emacs Manual}. | |
7015aca4 | 653 | |
35244a0e DL |
654 | @deffn Command forward-list &optional arg |
655 | This function moves forward across @var{arg} (default 1) balanced groups of | |
a890e1b0 RS |
656 | parentheses. (Other syntactic entities such as words or paired string |
657 | quotes are ignored.) | |
7015aca4 RS |
658 | @end deffn |
659 | ||
35244a0e DL |
660 | @deffn Command backward-list &optional arg |
661 | This function moves backward across @var{arg} (default 1) balanced groups of | |
a890e1b0 RS |
662 | parentheses. (Other syntactic entities such as words or paired string |
663 | quotes are ignored.) | |
7015aca4 RS |
664 | @end deffn |
665 | ||
35244a0e DL |
666 | @deffn Command up-list &optional arg |
667 | This function moves forward out of @var{arg} (default 1) levels of parentheses. | |
7015aca4 RS |
668 | A negative argument means move backward but still to a less deep spot. |
669 | @end deffn | |
670 | ||
35244a0e | 671 | @deffn Command down-list &optional arg |
bf4fb025 LT |
672 | This function moves forward into @var{arg} (default 1) levels of |
673 | parentheses. A negative argument means move backward but still go | |
ec221d13 | 674 | deeper in parentheses (@minus{}@var{arg} levels). |
7015aca4 RS |
675 | @end deffn |
676 | ||
35244a0e DL |
677 | @deffn Command forward-sexp &optional arg |
678 | This function moves forward across @var{arg} (default 1) balanced expressions. | |
a890e1b0 | 679 | Balanced expressions include both those delimited by parentheses and |
07af3024 | 680 | other kinds, such as words and string constants. |
47ab3ab3 | 681 | @xref{Parsing Expressions}. For example, |
7015aca4 RS |
682 | |
683 | @example | |
684 | @group | |
685 | ---------- Buffer: foo ---------- | |
686 | (concat@point{} "foo " (car x) y z) | |
687 | ---------- Buffer: foo ---------- | |
688 | @end group | |
689 | ||
690 | @group | |
691 | (forward-sexp 3) | |
692 | @result{} nil | |
693 | ||
694 | ---------- Buffer: foo ---------- | |
695 | (concat "foo " (car x) y@point{} z) | |
696 | ---------- Buffer: foo ---------- | |
697 | @end group | |
698 | @end example | |
699 | @end deffn | |
700 | ||
35244a0e DL |
701 | @deffn Command backward-sexp &optional arg |
702 | This function moves backward across @var{arg} (default 1) balanced expressions. | |
7015aca4 RS |
703 | @end deffn |
704 | ||
bf4fb025 | 705 | @deffn Command beginning-of-defun &optional arg |
a890e1b0 RS |
706 | This function moves back to the @var{arg}th beginning of a defun. If |
707 | @var{arg} is negative, this actually moves forward, but it still moves | |
938183e5 RS |
708 | to the beginning of a defun, not to the end of one. @var{arg} defaults |
709 | to 1. | |
a890e1b0 RS |
710 | @end deffn |
711 | ||
bf4fb025 | 712 | @deffn Command end-of-defun &optional arg |
29679a81 RS |
713 | This function moves forward to the @var{arg}th end of a defun. If |
714 | @var{arg} is negative, this actually moves backward, but it still moves | |
938183e5 RS |
715 | to the end of a defun, not to the beginning of one. @var{arg} defaults |
716 | to 1. | |
a890e1b0 RS |
717 | @end deffn |
718 | ||
719 | @defopt defun-prompt-regexp | |
475aab0d CY |
720 | If non-@code{nil}, this buffer-local variable holds a regular |
721 | expression that specifies what text can appear before the | |
722 | open-parenthesis that starts a defun. That is to say, a defun begins | |
723 | on a line that starts with a match for this regular expression, | |
724 | followed by a character with open-parenthesis syntax. | |
a890e1b0 RS |
725 | @end defopt |
726 | ||
3a420809 EZ |
727 | @defopt open-paren-in-column-0-is-defun-start |
728 | If this variable's value is non-@code{nil}, an open parenthesis in | |
729 | column 0 is considered to be the start of a defun. If it is | |
730 | @code{nil}, an open parenthesis in column 0 has no special meaning. | |
731 | The default is @code{t}. | |
732 | @end defopt | |
733 | ||
02b14400 | 734 | @defvar beginning-of-defun-function |
02b14400 RS |
735 | If non-@code{nil}, this variable holds a function for finding the |
736 | beginning of a defun. The function @code{beginning-of-defun} | |
737 | calls this function instead of using its normal method. | |
738 | @end defvar | |
739 | ||
740 | @defvar end-of-defun-function | |
02b14400 RS |
741 | If non-@code{nil}, this variable holds a function for finding the end of |
742 | a defun. The function @code{end-of-defun} calls this function instead | |
743 | of using its normal method. | |
744 | @end defvar | |
745 | ||
7015aca4 RS |
746 | @node Skipping Characters |
747 | @comment node-name, next, previous, up | |
748 | @subsection Skipping Characters | |
749 | @cindex skipping characters | |
750 | ||
751 | The following two functions move point over a specified set of | |
752 | characters. For example, they are often used to skip whitespace. For | |
753 | related functions, see @ref{Motion and Syntax}. | |
754 | ||
6d29587b DL |
755 | These functions convert the set string to multibyte if the buffer is |
756 | multibyte, and they convert it to unibyte if the buffer is unibyte, as | |
757 | the search functions do (@pxref{Searching and Matching}). | |
758 | ||
7015aca4 RS |
759 | @defun skip-chars-forward character-set &optional limit |
760 | This function moves point in the current buffer forward, skipping over a | |
761 | given set of characters. It examines the character following point, | |
762 | then advances point if the character matches @var{character-set}. This | |
763 | continues until it reaches a character that does not match. The | |
1911e6e5 | 764 | function returns the number of characters moved over. |
7015aca4 | 765 | |
938183e5 RS |
766 | The argument @var{character-set} is a string, like the inside of a |
767 | @samp{[@dots{}]} in a regular expression except that @samp{]} does not | |
768 | terminate it, and @samp{\} quotes @samp{^}, @samp{-} or @samp{\}. | |
769 | Thus, @code{"a-zA-Z"} skips over all letters, stopping before the | |
770 | first nonletter, and @code{"^a-zA-Z"} skips nonletters stopping before | |
543bc1b0 RS |
771 | the first letter. See @xref{Regular Expressions}. Character classes |
772 | can also be used, e.g. @code{"[:alnum:]"}. See @pxref{Char Classes}. | |
7015aca4 RS |
773 | |
774 | If @var{limit} is supplied (it must be a number or a marker), it | |
775 | specifies the maximum position in the buffer that point can be skipped | |
776 | to. Point will stop at or before @var{limit}. | |
777 | ||
778 | In the following example, point is initially located directly before the | |
779 | @samp{T}. After the form is evaluated, point is located at the end of | |
780 | that line (between the @samp{t} of @samp{hat} and the newline). The | |
781 | function skips all letters and spaces, but not newlines. | |
782 | ||
783 | @example | |
784 | @group | |
785 | ---------- Buffer: foo ---------- | |
786 | I read "@point{}The cat in the hat | |
787 | comes back" twice. | |
788 | ---------- Buffer: foo ---------- | |
789 | @end group | |
790 | ||
791 | @group | |
792 | (skip-chars-forward "a-zA-Z ") | |
793 | @result{} nil | |
794 | ||
795 | ---------- Buffer: foo ---------- | |
796 | I read "The cat in the hat@point{} | |
797 | comes back" twice. | |
798 | ---------- Buffer: foo ---------- | |
799 | @end group | |
800 | @end example | |
977f0dab | 801 | @end defun |
6d29587b | 802 | |
7015aca4 RS |
803 | @defun skip-chars-backward character-set &optional limit |
804 | This function moves point backward, skipping characters that match | |
f9f59935 | 805 | @var{character-set}, until @var{limit}. It is just like |
7015aca4 | 806 | @code{skip-chars-forward} except for the direction of motion. |
1911e6e5 RS |
807 | |
808 | The return value indicates the distance traveled. It is an integer that | |
809 | is zero or less. | |
7015aca4 RS |
810 | @end defun |
811 | ||
812 | @node Excursions | |
813 | @section Excursions | |
814 | @cindex excursion | |
815 | ||
816 | It is often useful to move point ``temporarily'' within a localized | |
817 | portion of the program, or to switch buffers temporarily. This is | |
818 | called an @dfn{excursion}, and it is done with the @code{save-excursion} | |
8241495d RS |
819 | special form. This construct initially remembers the identity of the |
820 | current buffer, and its values of point and the mark, and restores them | |
821 | after the completion of the excursion. | |
7015aca4 RS |
822 | |
823 | The forms for saving and restoring the configuration of windows are | |
824 | described elsewhere (see @ref{Window Configurations}, and @pxref{Frame | |
825 | Configurations}). | |
826 | ||
248a47c9 | 827 | @defspec save-excursion body@dots{} |
7015aca4 RS |
828 | @cindex mark excursion |
829 | @cindex point excursion | |
830 | @cindex current buffer excursion | |
831 | The @code{save-excursion} special form saves the identity of the current | |
29679a81 | 832 | buffer and the values of point and the mark in it, evaluates |
248a47c9 | 833 | @var{body}, and finally restores the buffer and its saved values of |
29679a81 RS |
834 | point and the mark. All three saved values are restored even in case of |
835 | an abnormal exit via @code{throw} or error (@pxref{Nonlocal Exits}). | |
7015aca4 RS |
836 | |
837 | The @code{save-excursion} special form is the standard way to switch | |
838 | buffers or move point within one part of a program and avoid affecting | |
a9f0a989 | 839 | the rest of the program. It is used more than 4000 times in the Lisp |
7015aca4 RS |
840 | sources of Emacs. |
841 | ||
842 | @code{save-excursion} does not save the values of point and the mark for | |
843 | other buffers, so changes in other buffers remain in effect after | |
844 | @code{save-excursion} exits. | |
845 | ||
846 | @cindex window excursions | |
847 | Likewise, @code{save-excursion} does not restore window-buffer | |
848 | correspondences altered by functions such as @code{switch-to-buffer}. | |
849 | One way to restore these correspondences, and the selected window, is to | |
850 | use @code{save-window-excursion} inside @code{save-excursion} | |
851 | (@pxref{Window Configurations}). | |
852 | ||
248a47c9 JL |
853 | The value returned by @code{save-excursion} is the result of the last |
854 | form in @var{body}, or @code{nil} if no body forms were given. | |
7015aca4 RS |
855 | |
856 | @example | |
857 | @group | |
7dd3d99f | 858 | (save-excursion @var{forms}) |
7015aca4 RS |
859 | @equiv{} |
860 | (let ((old-buf (current-buffer)) | |
861 | (old-pnt (point-marker)) | |
7dd3d99f | 862 | @end group |
7015aca4 RS |
863 | (old-mark (copy-marker (mark-marker)))) |
864 | (unwind-protect | |
865 | (progn @var{forms}) | |
866 | (set-buffer old-buf) | |
7dd3d99f | 867 | @group |
7015aca4 RS |
868 | (goto-char old-pnt) |
869 | (set-marker (mark-marker) old-mark))) | |
870 | @end group | |
871 | @end example | |
872 | @end defspec | |
873 | ||
a9f0a989 RS |
874 | @strong{Warning:} Ordinary insertion of text adjacent to the saved |
875 | point value relocates the saved value, just as it relocates all markers. | |
bf4fb025 LT |
876 | More precisely, the saved value is a marker with insertion type |
877 | @code{nil}. @xref{Marker Insertion Types}. Therefore, when the saved | |
878 | point value is restored, it normally comes before the inserted text. | |
a9f0a989 | 879 | |
969fe9b5 RS |
880 | Although @code{save-excursion} saves the location of the mark, it does |
881 | not prevent functions which modify the buffer from setting | |
882 | @code{deactivate-mark}, and thus causing the deactivation of the mark | |
883 | after the command finishes. @xref{The Mark}. | |
884 | ||
7015aca4 RS |
885 | @node Narrowing |
886 | @section Narrowing | |
887 | @cindex narrowing | |
888 | @cindex restriction (in a buffer) | |
889 | @cindex accessible portion (of a buffer) | |
890 | ||
891 | @dfn{Narrowing} means limiting the text addressable by Emacs editing | |
892 | commands to a limited range of characters in a buffer. The text that | |
893 | remains addressable is called the @dfn{accessible portion} of the | |
894 | buffer. | |
895 | ||
896 | Narrowing is specified with two buffer positions which become the | |
897 | beginning and end of the accessible portion. For most editing commands | |
898 | and most Emacs primitives, these positions replace the values of the | |
899 | beginning and end of the buffer. While narrowing is in effect, no text | |
900 | outside the accessible portion is displayed, and point cannot move | |
901 | outside the accessible portion. | |
902 | ||
29679a81 | 903 | Values such as positions or line numbers, which usually count from the |
7015aca4 RS |
904 | beginning of the buffer, do so despite narrowing, but the functions |
905 | which use them refuse to operate on text that is inaccessible. | |
906 | ||
907 | The commands for saving buffers are unaffected by narrowing; they save | |
29679a81 | 908 | the entire buffer regardless of any narrowing. |
7015aca4 RS |
909 | |
910 | @deffn Command narrow-to-region start end | |
911 | This function sets the accessible portion of the current buffer to start | |
912 | at @var{start} and end at @var{end}. Both arguments should be character | |
913 | positions. | |
914 | ||
915 | In an interactive call, @var{start} and @var{end} are set to the bounds | |
916 | of the current region (point and the mark, with the smallest first). | |
917 | @end deffn | |
918 | ||
bf4fb025 | 919 | @deffn Command narrow-to-page &optional move-count |
7015aca4 RS |
920 | This function sets the accessible portion of the current buffer to |
921 | include just the current page. An optional first argument | |
922 | @var{move-count} non-@code{nil} means to move forward or backward by | |
f9f59935 | 923 | @var{move-count} pages and then narrow to one page. The variable |
7015aca4 RS |
924 | @code{page-delimiter} specifies where pages start and end |
925 | (@pxref{Standard Regexps}). | |
926 | ||
927 | In an interactive call, @var{move-count} is set to the numeric prefix | |
928 | argument. | |
929 | @end deffn | |
930 | ||
931 | @deffn Command widen | |
932 | @cindex widening | |
933 | This function cancels any narrowing in the current buffer, so that the | |
934 | entire contents are accessible. This is called @dfn{widening}. | |
935 | It is equivalent to the following expression: | |
936 | ||
937 | @example | |
938 | (narrow-to-region 1 (1+ (buffer-size))) | |
939 | @end example | |
940 | @end deffn | |
941 | ||
942 | @defspec save-restriction body@dots{} | |
943 | This special form saves the current bounds of the accessible portion, | |
944 | evaluates the @var{body} forms, and finally restores the saved bounds, | |
945 | thus restoring the same state of narrowing (or absence thereof) formerly | |
946 | in effect. The state of narrowing is restored even in the event of an | |
29679a81 RS |
947 | abnormal exit via @code{throw} or error (@pxref{Nonlocal Exits}). |
948 | Therefore, this construct is a clean way to narrow a buffer temporarily. | |
7015aca4 RS |
949 | |
950 | The value returned by @code{save-restriction} is that returned by the | |
951 | last form in @var{body}, or @code{nil} if no body forms were given. | |
952 | ||
953 | @c Wordy to avoid overfull hbox. --rjc 16mar92 | |
954 | @strong{Caution:} it is easy to make a mistake when using the | |
955 | @code{save-restriction} construct. Read the entire description here | |
956 | before you try it. | |
957 | ||
958 | If @var{body} changes the current buffer, @code{save-restriction} still | |
959 | restores the restrictions on the original buffer (the buffer whose | |
f9f59935 | 960 | restrictions it saved from), but it does not restore the identity of the |
7015aca4 RS |
961 | current buffer. |
962 | ||
963 | @code{save-restriction} does @emph{not} restore point and the mark; use | |
964 | @code{save-excursion} for that. If you use both @code{save-restriction} | |
965 | and @code{save-excursion} together, @code{save-excursion} should come | |
966 | first (on the outside). Otherwise, the old point value would be | |
967 | restored with temporary narrowing still in effect. If the old point | |
968 | value were outside the limits of the temporary narrowing, this would | |
969 | fail to restore it accurately. | |
970 | ||
7015aca4 RS |
971 | Here is a simple example of correct use of @code{save-restriction}: |
972 | ||
973 | @example | |
974 | @group | |
975 | ---------- Buffer: foo ---------- | |
976 | This is the contents of foo | |
977 | This is the contents of foo | |
978 | This is the contents of foo@point{} | |
979 | ---------- Buffer: foo ---------- | |
980 | @end group | |
981 | ||
982 | @group | |
983 | (save-excursion | |
984 | (save-restriction | |
985 | (goto-char 1) | |
986 | (forward-line 2) | |
987 | (narrow-to-region 1 (point)) | |
988 | (goto-char (point-min)) | |
989 | (replace-string "foo" "bar"))) | |
990 | ||
991 | ---------- Buffer: foo ---------- | |
992 | This is the contents of bar | |
993 | This is the contents of bar | |
994 | This is the contents of foo@point{} | |
995 | ---------- Buffer: foo ---------- | |
996 | @end group | |
997 | @end example | |
998 | @end defspec | |
ab5796a9 MB |
999 | |
1000 | @ignore | |
1001 | arch-tag: 56e8ff26-4ffe-4832-a141-7e991a2d0f87 | |
1002 | @end ignore |