| 1 | @c -*-texinfo-*- |
| 2 | @c This is part of the GNU Emacs Lisp Reference Manual. |
| 3 | @c Copyright (C) 1990, 1991, 1992, 1993, 1994 Free Software Foundation, Inc. |
| 4 | @c See the file elisp.texi for copying conditions. |
| 5 | @setfilename ../info/strings |
| 6 | @node Strings and Characters, Lists, Numbers, Top |
| 7 | @comment node-name, next, previous, up |
| 8 | @chapter Strings and Characters |
| 9 | @cindex strings |
| 10 | @cindex character arrays |
| 11 | @cindex characters |
| 12 | @cindex bytes |
| 13 | |
| 14 | A string in Emacs Lisp is an array that contains an ordered sequence |
| 15 | of characters. Strings are used as names of symbols, buffers, and |
| 16 | files, to send messages to users, to hold text being copied between |
| 17 | buffers, and for many other purposes. Because strings are so important, |
| 18 | Emacs Lisp has many functions expressly for manipulating them. Emacs |
| 19 | Lisp programs use strings more often than individual characters. |
| 20 | |
| 21 | @xref{Strings of Events}, for special considerations for strings of |
| 22 | keyboard character events. |
| 23 | |
| 24 | @menu |
| 25 | * Basics: String Basics. Basic properties of strings and characters. |
| 26 | * Predicates for Strings:: Testing whether an object is a string or char. |
| 27 | * Creating Strings:: Functions to allocate new strings. |
| 28 | * Text Comparison:: Comparing characters or strings. |
| 29 | * String Conversion:: Converting characters or strings and vice versa. |
| 30 | * Formatting Strings:: @code{format}: Emacs's analog of @code{printf}. |
| 31 | * Character Case:: Case conversion functions. |
| 32 | * Case Table:: Customizing case conversion. |
| 33 | @end menu |
| 34 | |
| 35 | @node String Basics |
| 36 | @section String and Character Basics |
| 37 | |
| 38 | Strings in Emacs Lisp are arrays that contain an ordered sequence of |
| 39 | characters. Characters are represented in Emacs Lisp as integers; |
| 40 | whether an integer was intended as a character or not is determined only |
| 41 | by how it is used. Thus, strings really contain integers. |
| 42 | |
| 43 | The length of a string (like any array) is fixed and independent of |
| 44 | the string contents, and cannot be altered. Strings in Lisp are |
| 45 | @emph{not} terminated by a distinguished character code. (By contrast, |
| 46 | strings in C are terminated by a character with @sc{ASCII} code 0.) |
| 47 | This means that any character, including the null character (@sc{ASCII} |
| 48 | code 0), is a valid element of a string.@refill |
| 49 | |
| 50 | Since strings are considered arrays, you can operate on them with the |
| 51 | general array functions. (@xref{Sequences Arrays Vectors}.) For |
| 52 | example, you can access or change individual characters in a string |
| 53 | using the functions @code{aref} and @code{aset} (@pxref{Array |
| 54 | Functions}). |
| 55 | |
| 56 | Each character in a string is stored in a single byte. Therefore, |
| 57 | numbers not in the range 0 to 255 are truncated when stored into a |
| 58 | string. This means that a string takes up much less memory than a |
| 59 | vector of the same length. |
| 60 | |
| 61 | Sometimes key sequences are represented as strings. When a string is |
| 62 | a key sequence, string elements in the range 128 to 255 represent meta |
| 63 | characters (which are extremely large integers) rather than keyboard |
| 64 | events in the range 128 to 255. |
| 65 | |
| 66 | Strings cannot hold characters that have the hyper, super or alt |
| 67 | modifiers; they can hold @sc{ASCII} control characters, but no other |
| 68 | control characters. They do not distinguish case in @sc{ASCII} control |
| 69 | characters. @xref{Character Type}, for more information about |
| 70 | representation of meta and other modifiers for keyboard input |
| 71 | characters. |
| 72 | |
| 73 | Strings are useful for holding regular expressions. You can also |
| 74 | match regular expressions against strings (@pxref{Regexp Search}). The |
| 75 | functions @code{match-string} (@pxref{Simple Match Data}) and |
| 76 | @code{replace-match} (@pxref{Replacing Match}) are useful for |
| 77 | decomposing and modifying strings based on regular expression matching. |
| 78 | |
| 79 | Like a buffer, a string can contain text properties for the characters |
| 80 | in it, as well as the characters themselves. @xref{Text Properties}. |
| 81 | All the Lisp primitives that copy text from strings to buffers or other |
| 82 | strings also copy the properties of the characters being copied. |
| 83 | |
| 84 | @xref{Text}, for information about functions that display strings or |
| 85 | copy them into buffers. @xref{Character Type}, and @ref{String Type}, |
| 86 | for information about the syntax of characters and strings. |
| 87 | |
| 88 | @node Predicates for Strings |
| 89 | @section The Predicates for Strings |
| 90 | |
| 91 | For more information about general sequence and array predicates, |
| 92 | see @ref{Sequences Arrays Vectors}, and @ref{Arrays}. |
| 93 | |
| 94 | @defun stringp object |
| 95 | This function returns @code{t} if @var{object} is a string, @code{nil} |
| 96 | otherwise. |
| 97 | @end defun |
| 98 | |
| 99 | @defun char-or-string-p object |
| 100 | This function returns @code{t} if @var{object} is a string or a |
| 101 | character (i.e., an integer), @code{nil} otherwise. |
| 102 | @end defun |
| 103 | |
| 104 | @node Creating Strings |
| 105 | @section Creating Strings |
| 106 | |
| 107 | The following functions create strings, either from scratch, or by |
| 108 | putting strings together, or by taking them apart. |
| 109 | |
| 110 | @defun make-string count character |
| 111 | This function returns a string made up of @var{count} repetitions of |
| 112 | @var{character}. If @var{count} is negative, an error is signaled. |
| 113 | |
| 114 | @example |
| 115 | (make-string 5 ?x) |
| 116 | @result{} "xxxxx" |
| 117 | (make-string 0 ?x) |
| 118 | @result{} "" |
| 119 | @end example |
| 120 | |
| 121 | Other functions to compare with this one include @code{char-to-string} |
| 122 | (@pxref{String Conversion}), @code{make-vector} (@pxref{Vectors}), and |
| 123 | @code{make-list} (@pxref{Building Lists}). |
| 124 | @end defun |
| 125 | |
| 126 | @defun substring string start &optional end |
| 127 | This function returns a new string which consists of those characters |
| 128 | from @var{string} in the range from (and including) the character at the |
| 129 | index @var{start} up to (but excluding) the character at the index |
| 130 | @var{end}. The first character is at index zero. |
| 131 | |
| 132 | @example |
| 133 | @group |
| 134 | (substring "abcdefg" 0 3) |
| 135 | @result{} "abc" |
| 136 | @end group |
| 137 | @end example |
| 138 | |
| 139 | @noindent |
| 140 | Here the index for @samp{a} is 0, the index for @samp{b} is 1, and the |
| 141 | index for @samp{c} is 2. Thus, three letters, @samp{abc}, are copied |
| 142 | from the string @code{"abcdefg"}. The index 3 marks the character |
| 143 | position up to which the substring is copied. The character whose index |
| 144 | is 3 is actually the fourth character in the string. |
| 145 | |
| 146 | A negative number counts from the end of the string, so that @minus{}1 |
| 147 | signifies the index of the last character of the string. For example: |
| 148 | |
| 149 | @example |
| 150 | @group |
| 151 | (substring "abcdefg" -3 -1) |
| 152 | @result{} "ef" |
| 153 | @end group |
| 154 | @end example |
| 155 | |
| 156 | @noindent |
| 157 | In this example, the index for @samp{e} is @minus{}3, the index for |
| 158 | @samp{f} is @minus{}2, and the index for @samp{g} is @minus{}1. |
| 159 | Therefore, @samp{e} and @samp{f} are included, and @samp{g} is excluded. |
| 160 | |
| 161 | When @code{nil} is used as an index, it stands for the length of the |
| 162 | string. Thus, |
| 163 | |
| 164 | @example |
| 165 | @group |
| 166 | (substring "abcdefg" -3 nil) |
| 167 | @result{} "efg" |
| 168 | @end group |
| 169 | @end example |
| 170 | |
| 171 | Omitting the argument @var{end} is equivalent to specifying @code{nil}. |
| 172 | It follows that @code{(substring @var{string} 0)} returns a copy of all |
| 173 | of @var{string}. |
| 174 | |
| 175 | @example |
| 176 | @group |
| 177 | (substring "abcdefg" 0) |
| 178 | @result{} "abcdefg" |
| 179 | @end group |
| 180 | @end example |
| 181 | |
| 182 | @noindent |
| 183 | But we recommend @code{copy-sequence} for this purpose (@pxref{Sequence |
| 184 | Functions}). |
| 185 | |
| 186 | If the characters copied from @var{string} have text properties, the |
| 187 | properties are copied into the new string also. @xref{Text Properties}. |
| 188 | |
| 189 | A @code{wrong-type-argument} error is signaled if either @var{start} or |
| 190 | @var{end} is not an integer or @code{nil}. An @code{args-out-of-range} |
| 191 | error is signaled if @var{start} indicates a character following |
| 192 | @var{end}, or if either integer is out of range for @var{string}. |
| 193 | |
| 194 | Contrast this function with @code{buffer-substring} (@pxref{Buffer |
| 195 | Contents}), which returns a string containing a portion of the text in |
| 196 | the current buffer. The beginning of a string is at index 0, but the |
| 197 | beginning of a buffer is at index 1. |
| 198 | @end defun |
| 199 | |
| 200 | @defun concat &rest sequences |
| 201 | @cindex copying strings |
| 202 | @cindex concatenating strings |
| 203 | This function returns a new string consisting of the characters in the |
| 204 | arguments passed to it (along with their text properties, if any). The |
| 205 | arguments may be strings, lists of numbers, or vectors of numbers; they |
| 206 | are not themselves changed. If @code{concat} receives no arguments, it |
| 207 | returns an empty string. |
| 208 | |
| 209 | @example |
| 210 | (concat "abc" "-def") |
| 211 | @result{} "abc-def" |
| 212 | (concat "abc" (list 120 (+ 256 121)) [122]) |
| 213 | @result{} "abcxyz" |
| 214 | ;; @r{@code{nil} is an empty sequence.} |
| 215 | (concat "abc" nil "-def") |
| 216 | @result{} "abc-def" |
| 217 | (concat "The " "quick brown " "fox.") |
| 218 | @result{} "The quick brown fox." |
| 219 | (concat) |
| 220 | @result{} "" |
| 221 | @end example |
| 222 | |
| 223 | @noindent |
| 224 | The second example above shows how characters stored in strings are |
| 225 | taken modulo 256. In other words, each character in the string is |
| 226 | stored in one byte. |
| 227 | |
| 228 | The @code{concat} function always constructs a new string that is |
| 229 | not @code{eq} to any existing string. |
| 230 | |
| 231 | When an argument is an integer (not a sequence of integers), it is |
| 232 | converted to a string of digits making up the decimal printed |
| 233 | representation of the integer. @strong{Don't use this feature; we plan |
| 234 | to eliminate it. If you already use this feature, change your programs |
| 235 | now!} The proper way to convert an integer to a decimal number in this |
| 236 | way is with @code{format} (@pxref{Formatting Strings}) or |
| 237 | @code{number-to-string} (@pxref{String Conversion}). |
| 238 | |
| 239 | @example |
| 240 | @group |
| 241 | (concat 137) |
| 242 | @result{} "137" |
| 243 | (concat 54 321) |
| 244 | @result{} "54321" |
| 245 | @end group |
| 246 | @end example |
| 247 | |
| 248 | For information about other concatenation functions, see the |
| 249 | description of @code{mapconcat} in @ref{Mapping Functions}, |
| 250 | @code{vconcat} in @ref{Vectors}, and @code{append} in @ref{Building |
| 251 | Lists}. |
| 252 | @end defun |
| 253 | |
| 254 | @need 2000 |
| 255 | @node Text Comparison |
| 256 | @section Comparison of Characters and Strings |
| 257 | @cindex string equality |
| 258 | |
| 259 | @defun char-equal character1 character2 |
| 260 | This function returns @code{t} if the arguments represent the same |
| 261 | character, @code{nil} otherwise. This function ignores differences |
| 262 | in case if @code{case-fold-search} is non-@code{nil}. |
| 263 | |
| 264 | @example |
| 265 | (char-equal ?x ?x) |
| 266 | @result{} t |
| 267 | (char-to-string (+ 256 ?x)) |
| 268 | @result{} "x" |
| 269 | (char-equal ?x (+ 256 ?x)) |
| 270 | @result{} t |
| 271 | @end example |
| 272 | @end defun |
| 273 | |
| 274 | @defun string= string1 string2 |
| 275 | This function returns @code{t} if the characters of the two strings |
| 276 | match exactly; case is significant. |
| 277 | |
| 278 | @example |
| 279 | (string= "abc" "abc") |
| 280 | @result{} t |
| 281 | (string= "abc" "ABC") |
| 282 | @result{} nil |
| 283 | (string= "ab" "ABC") |
| 284 | @result{} nil |
| 285 | @end example |
| 286 | |
| 287 | The function @code{string=} ignores the text properties of the |
| 288 | two strings. To compare strings in a way that compares their text |
| 289 | properties also, use @code{equal} (@pxref{Equality Predicates}). |
| 290 | @end defun |
| 291 | |
| 292 | @defun string-equal string1 string2 |
| 293 | @code{string-equal} is another name for @code{string=}. |
| 294 | @end defun |
| 295 | |
| 296 | @cindex lexical comparison |
| 297 | @defun string< string1 string2 |
| 298 | @c (findex string< causes problems for permuted index!!) |
| 299 | This function compares two strings a character at a time. First it |
| 300 | scans both the strings at once to find the first pair of corresponding |
| 301 | characters that do not match. If the lesser character of those two is |
| 302 | the character from @var{string1}, then @var{string1} is less, and this |
| 303 | function returns @code{t}. If the lesser character is the one from |
| 304 | @var{string2}, then @var{string1} is greater, and this function returns |
| 305 | @code{nil}. If the two strings match entirely, the value is @code{nil}. |
| 306 | |
| 307 | Pairs of characters are compared by their @sc{ASCII} codes. Keep in |
| 308 | mind that lower case letters have higher numeric values in the |
| 309 | @sc{ASCII} character set than their upper case counterparts; numbers and |
| 310 | many punctuation characters have a lower numeric value than upper case |
| 311 | letters. |
| 312 | |
| 313 | @example |
| 314 | @group |
| 315 | (string< "abc" "abd") |
| 316 | @result{} t |
| 317 | (string< "abd" "abc") |
| 318 | @result{} nil |
| 319 | (string< "123" "abc") |
| 320 | @result{} t |
| 321 | @end group |
| 322 | @end example |
| 323 | |
| 324 | When the strings have different lengths, and they match up to the |
| 325 | length of @var{string1}, then the result is @code{t}. If they match up |
| 326 | to the length of @var{string2}, the result is @code{nil}. A string of |
| 327 | no characters is less than any other string. |
| 328 | |
| 329 | @example |
| 330 | @group |
| 331 | (string< "" "abc") |
| 332 | @result{} t |
| 333 | (string< "ab" "abc") |
| 334 | @result{} t |
| 335 | (string< "abc" "") |
| 336 | @result{} nil |
| 337 | (string< "abc" "ab") |
| 338 | @result{} nil |
| 339 | (string< "" "") |
| 340 | @result{} nil |
| 341 | @end group |
| 342 | @end example |
| 343 | @end defun |
| 344 | |
| 345 | @defun string-lessp string1 string2 |
| 346 | @code{string-lessp} is another name for @code{string<}. |
| 347 | @end defun |
| 348 | |
| 349 | See also @code{compare-buffer-substrings} in @ref{Comparing Text}, for |
| 350 | a way to compare text in buffers. The function @code{string-match}, |
| 351 | which matches a regular expression against a string, can be used |
| 352 | for a kind of string comparison; see @ref{Regexp Search}. |
| 353 | |
| 354 | @node String Conversion |
| 355 | @comment node-name, next, previous, up |
| 356 | @section Conversion of Characters and Strings |
| 357 | @cindex conversion of strings |
| 358 | |
| 359 | This section describes functions for conversions between characters, |
| 360 | strings and integers. @code{format} and @code{prin1-to-string} |
| 361 | (@pxref{Output Functions}) can also convert Lisp objects into strings. |
| 362 | @code{read-from-string} (@pxref{Input Functions}) can ``convert'' a |
| 363 | string representation of a Lisp object into an object. |
| 364 | |
| 365 | @xref{Documentation}, for functions that produce textual descriptions |
| 366 | of text characters and general input events |
| 367 | (@code{single-key-description} and @code{text-char-description}). These |
| 368 | functions are used primarily for making help messages. |
| 369 | |
| 370 | @defun char-to-string character |
| 371 | @cindex character to string |
| 372 | This function returns a new string with a length of one character. |
| 373 | The value of @var{character}, modulo 256, is used to initialize the |
| 374 | element of the string. |
| 375 | |
| 376 | This function is similar to @code{make-string} with an integer argument |
| 377 | of 1. (@xref{Creating Strings}.) This conversion can also be done with |
| 378 | @code{format} using the @samp{%c} format specification. |
| 379 | (@xref{Formatting Strings}.) |
| 380 | |
| 381 | @example |
| 382 | (char-to-string ?x) |
| 383 | @result{} "x" |
| 384 | (char-to-string (+ 256 ?x)) |
| 385 | @result{} "x" |
| 386 | (make-string 1 ?x) |
| 387 | @result{} "x" |
| 388 | @end example |
| 389 | @end defun |
| 390 | |
| 391 | @defun string-to-char string |
| 392 | @cindex string to character |
| 393 | This function returns the first character in @var{string}. If the |
| 394 | string is empty, the function returns 0. The value is also 0 when the |
| 395 | first character of @var{string} is the null character, @sc{ASCII} code |
| 396 | 0. |
| 397 | |
| 398 | @example |
| 399 | (string-to-char "ABC") |
| 400 | @result{} 65 |
| 401 | (string-to-char "xyz") |
| 402 | @result{} 120 |
| 403 | (string-to-char "") |
| 404 | @result{} 0 |
| 405 | (string-to-char "\000") |
| 406 | @result{} 0 |
| 407 | @end example |
| 408 | |
| 409 | This function may be eliminated in the future if it does not seem useful |
| 410 | enough to retain. |
| 411 | @end defun |
| 412 | |
| 413 | @defun number-to-string number |
| 414 | @cindex integer to string |
| 415 | @cindex integer to decimal |
| 416 | This function returns a string consisting of the printed |
| 417 | representation of @var{number}, which may be an integer or a floating |
| 418 | point number. The value starts with a sign if the argument is |
| 419 | negative. |
| 420 | |
| 421 | @example |
| 422 | (number-to-string 256) |
| 423 | @result{} "256" |
| 424 | (number-to-string -23) |
| 425 | @result{} "-23" |
| 426 | (number-to-string -23.5) |
| 427 | @result{} "-23.5" |
| 428 | @end example |
| 429 | |
| 430 | @cindex int-to-string |
| 431 | @code{int-to-string} is a semi-obsolete alias for this function. |
| 432 | |
| 433 | See also the function @code{format} in @ref{Formatting Strings}. |
| 434 | @end defun |
| 435 | |
| 436 | @defun string-to-number string |
| 437 | @cindex string to number |
| 438 | This function returns the numeric value of the characters in |
| 439 | @var{string}, read in base ten. It skips spaces and tabs at the |
| 440 | beginning of @var{string}, then reads as much of @var{string} as it can |
| 441 | interpret as a number. (On some systems it ignores other whitespace at |
| 442 | the beginning, not just spaces and tabs.) If the first character after |
| 443 | the ignored whitespace is not a digit or a minus sign, this function |
| 444 | returns 0. |
| 445 | |
| 446 | @example |
| 447 | (string-to-number "256") |
| 448 | @result{} 256 |
| 449 | (string-to-number "25 is a perfect square.") |
| 450 | @result{} 25 |
| 451 | (string-to-number "X256") |
| 452 | @result{} 0 |
| 453 | (string-to-number "-4.5") |
| 454 | @result{} -4.5 |
| 455 | @end example |
| 456 | |
| 457 | @findex string-to-int |
| 458 | @code{string-to-int} is an obsolete alias for this function. |
| 459 | @end defun |
| 460 | |
| 461 | @node Formatting Strings |
| 462 | @comment node-name, next, previous, up |
| 463 | @section Formatting Strings |
| 464 | @cindex formatting strings |
| 465 | @cindex strings, formatting them |
| 466 | |
| 467 | @dfn{Formatting} means constructing a string by substitution of |
| 468 | computed values at various places in a constant string. This string |
| 469 | controls how the other values are printed as well as where they appear; |
| 470 | it is called a @dfn{format string}. |
| 471 | |
| 472 | Formatting is often useful for computing messages to be displayed. In |
| 473 | fact, the functions @code{message} and @code{error} provide the same |
| 474 | formatting feature described here; they differ from @code{format} only |
| 475 | in how they use the result of formatting. |
| 476 | |
| 477 | @defun format string &rest objects |
| 478 | This function returns a new string that is made by copying |
| 479 | @var{string} and then replacing any format specification |
| 480 | in the copy with encodings of the corresponding @var{objects}. The |
| 481 | arguments @var{objects} are the computed values to be formatted. |
| 482 | @end defun |
| 483 | |
| 484 | @cindex @samp{%} in format |
| 485 | @cindex format specification |
| 486 | A format specification is a sequence of characters beginning with a |
| 487 | @samp{%}. Thus, if there is a @samp{%d} in @var{string}, the |
| 488 | @code{format} function replaces it with the printed representation of |
| 489 | one of the values to be formatted (one of the arguments @var{objects}). |
| 490 | For example: |
| 491 | |
| 492 | @example |
| 493 | @group |
| 494 | (format "The value of fill-column is %d." fill-column) |
| 495 | @result{} "The value of fill-column is 72." |
| 496 | @end group |
| 497 | @end example |
| 498 | |
| 499 | If @var{string} contains more than one format specification, the |
| 500 | format specifications correspond with successive values from |
| 501 | @var{objects}. Thus, the first format specification in @var{string} |
| 502 | uses the first such value, the second format specification uses the |
| 503 | second such value, and so on. Any extra format specifications (those |
| 504 | for which there are no corresponding values) cause unpredictable |
| 505 | behavior. Any extra values to be formatted are ignored. |
| 506 | |
| 507 | Certain format specifications require values of particular types. |
| 508 | However, no error is signaled if the value actually supplied fails to |
| 509 | have the expected type. Instead, the output is likely to be |
| 510 | meaningless. |
| 511 | |
| 512 | Here is a table of valid format specifications: |
| 513 | |
| 514 | @table @samp |
| 515 | @item %s |
| 516 | Replace the specification with the printed representation of the object, |
| 517 | made without quoting. Thus, strings are represented by their contents |
| 518 | alone, with no @samp{"} characters, and symbols appear without @samp{\} |
| 519 | characters. |
| 520 | |
| 521 | If there is no corresponding object, the empty string is used. |
| 522 | |
| 523 | @item %S |
| 524 | Replace the specification with the printed representation of the object, |
| 525 | made with quoting. Thus, strings are enclosed in @samp{"} characters, |
| 526 | and @samp{\} characters appear where necessary before special characters. |
| 527 | |
| 528 | If there is no corresponding object, the empty string is used. |
| 529 | |
| 530 | @item %o |
| 531 | @cindex integer to octal |
| 532 | Replace the specification with the base-eight representation of an |
| 533 | integer. |
| 534 | |
| 535 | @item %d |
| 536 | Replace the specification with the base-ten representation of an |
| 537 | integer. |
| 538 | |
| 539 | @item %x |
| 540 | @cindex integer to hexadecimal |
| 541 | Replace the specification with the base-sixteen representation of an |
| 542 | integer. |
| 543 | |
| 544 | @item %c |
| 545 | Replace the specification with the character which is the value given. |
| 546 | |
| 547 | @item %e |
| 548 | Replace the specification with the exponential notation for a floating |
| 549 | point number. |
| 550 | |
| 551 | @item %f |
| 552 | Replace the specification with the decimal-point notation for a floating |
| 553 | point number. |
| 554 | |
| 555 | @item %g |
| 556 | Replace the specification with notation for a floating point number, |
| 557 | using either exponential notation or decimal-point notation whichever |
| 558 | is shorter. |
| 559 | |
| 560 | @item %% |
| 561 | A single @samp{%} is placed in the string. This format specification is |
| 562 | unusual in that it does not use a value. For example, @code{(format "%% |
| 563 | %d" 30)} returns @code{"% 30"}. |
| 564 | @end table |
| 565 | |
| 566 | Any other format character results in an @samp{Invalid format |
| 567 | operation} error. |
| 568 | |
| 569 | Here are several examples: |
| 570 | |
| 571 | @example |
| 572 | @group |
| 573 | (format "The name of this buffer is %s." (buffer-name)) |
| 574 | @result{} "The name of this buffer is strings.texi." |
| 575 | |
| 576 | (format "The buffer object prints as %s." (current-buffer)) |
| 577 | @result{} "The buffer object prints as strings.texi." |
| 578 | |
| 579 | (format "The octal value of %d is %o, |
| 580 | and the hex value is %x." 18 18 18) |
| 581 | @result{} "The octal value of 18 is 22, |
| 582 | and the hex value is 12." |
| 583 | @end group |
| 584 | @end example |
| 585 | |
| 586 | @cindex numeric prefix |
| 587 | @cindex field width |
| 588 | @cindex padding |
| 589 | All the specification characters allow an optional numeric prefix |
| 590 | between the @samp{%} and the character. The optional numeric prefix |
| 591 | defines the minimum width for the object. If the printed representation |
| 592 | of the object contains fewer characters than this, then it is padded. |
| 593 | The padding is on the left if the prefix is positive (or starts with |
| 594 | zero) and on the right if the prefix is negative. The padding character |
| 595 | is normally a space, but if the numeric prefix starts with a zero, zeros |
| 596 | are used for padding. |
| 597 | |
| 598 | @example |
| 599 | (format "%06d is padded on the left with zeros" 123) |
| 600 | @result{} "000123 is padded on the left with zeros" |
| 601 | |
| 602 | (format "%-6d is padded on the right" 123) |
| 603 | @result{} "123 is padded on the right" |
| 604 | @end example |
| 605 | |
| 606 | @code{format} never truncates an object's printed representation, no |
| 607 | matter what width you specify. Thus, you can use a numeric prefix to |
| 608 | specify a minimum spacing between columns with no risk of losing |
| 609 | information. |
| 610 | |
| 611 | In the following three examples, @samp{%7s} specifies a minimum width |
| 612 | of 7. In the first case, the string inserted in place of @samp{%7s} has |
| 613 | only 3 letters, so 4 blank spaces are inserted for padding. In the |
| 614 | second case, the string @code{"specification"} is 13 letters wide but is |
| 615 | not truncated. In the third case, the padding is on the right. |
| 616 | |
| 617 | @smallexample |
| 618 | @group |
| 619 | (format "The word `%7s' actually has %d letters in it." |
| 620 | "foo" (length "foo")) |
| 621 | @result{} "The word ` foo' actually has 3 letters in it." |
| 622 | @end group |
| 623 | |
| 624 | @group |
| 625 | (format "The word `%7s' actually has %d letters in it." |
| 626 | "specification" (length "specification")) |
| 627 | @result{} "The word `specification' actually has 13 letters in it." |
| 628 | @end group |
| 629 | |
| 630 | @group |
| 631 | (format "The word `%-7s' actually has %d letters in it." |
| 632 | "foo" (length "foo")) |
| 633 | @result{} "The word `foo ' actually has 3 letters in it." |
| 634 | @end group |
| 635 | @end smallexample |
| 636 | |
| 637 | @node Character Case |
| 638 | @comment node-name, next, previous, up |
| 639 | @section Character Case |
| 640 | @cindex upper case |
| 641 | @cindex lower case |
| 642 | @cindex character case |
| 643 | |
| 644 | The character case functions change the case of single characters or |
| 645 | of the contents of strings. The functions convert only alphabetic |
| 646 | characters (the letters @samp{A} through @samp{Z} and @samp{a} through |
| 647 | @samp{z}); other characters are not altered. The functions do not |
| 648 | modify the strings that are passed to them as arguments. |
| 649 | |
| 650 | The examples below use the characters @samp{X} and @samp{x} which have |
| 651 | @sc{ASCII} codes 88 and 120 respectively. |
| 652 | |
| 653 | @defun downcase string-or-char |
| 654 | This function converts a character or a string to lower case. |
| 655 | |
| 656 | When the argument to @code{downcase} is a string, the function creates |
| 657 | and returns a new string in which each letter in the argument that is |
| 658 | upper case is converted to lower case. When the argument to |
| 659 | @code{downcase} is a character, @code{downcase} returns the |
| 660 | corresponding lower case character. This value is an integer. If the |
| 661 | original character is lower case, or is not a letter, then the value |
| 662 | equals the original character. |
| 663 | |
| 664 | @example |
| 665 | (downcase "The cat in the hat") |
| 666 | @result{} "the cat in the hat" |
| 667 | |
| 668 | (downcase ?X) |
| 669 | @result{} 120 |
| 670 | @end example |
| 671 | @end defun |
| 672 | |
| 673 | @defun upcase string-or-char |
| 674 | This function converts a character or a string to upper case. |
| 675 | |
| 676 | When the argument to @code{upcase} is a string, the function creates |
| 677 | and returns a new string in which each letter in the argument that is |
| 678 | lower case is converted to upper case. |
| 679 | |
| 680 | When the argument to @code{upcase} is a character, @code{upcase} |
| 681 | returns the corresponding upper case character. This value is an integer. |
| 682 | If the original character is upper case, or is not a letter, then the |
| 683 | value equals the original character. |
| 684 | |
| 685 | @example |
| 686 | (upcase "The cat in the hat") |
| 687 | @result{} "THE CAT IN THE HAT" |
| 688 | |
| 689 | (upcase ?x) |
| 690 | @result{} 88 |
| 691 | @end example |
| 692 | @end defun |
| 693 | |
| 694 | @defun capitalize string-or-char |
| 695 | @cindex capitalization |
| 696 | This function capitalizes strings or characters. If |
| 697 | @var{string-or-char} is a string, the function creates and returns a new |
| 698 | string, whose contents are a copy of @var{string-or-char} in which each |
| 699 | word has been capitalized. This means that the first character of each |
| 700 | word is converted to upper case, and the rest are converted to lower |
| 701 | case. |
| 702 | |
| 703 | The definition of a word is any sequence of consecutive characters that |
| 704 | are assigned to the word constituent syntax class in the current syntax |
| 705 | table (@xref{Syntax Class Table}). |
| 706 | |
| 707 | When the argument to @code{capitalize} is a character, @code{capitalize} |
| 708 | has the same result as @code{upcase}. |
| 709 | |
| 710 | @example |
| 711 | (capitalize "The cat in the hat") |
| 712 | @result{} "The Cat In The Hat" |
| 713 | |
| 714 | (capitalize "THE 77TH-HATTED CAT") |
| 715 | @result{} "The 77th-Hatted Cat" |
| 716 | |
| 717 | @group |
| 718 | (capitalize ?x) |
| 719 | @result{} 88 |
| 720 | @end group |
| 721 | @end example |
| 722 | @end defun |
| 723 | |
| 724 | @node Case Table |
| 725 | @section The Case Table |
| 726 | |
| 727 | You can customize case conversion by installing a special @dfn{case |
| 728 | table}. A case table specifies the mapping between upper case and lower |
| 729 | case letters. It affects both the string and character case conversion |
| 730 | functions (see the previous section) and those that apply to text in the |
| 731 | buffer (@pxref{Case Changes}). You need a case table if you are using a |
| 732 | language which has letters other than the standard @sc{ASCII} letters. |
| 733 | |
| 734 | A case table is a list of this form: |
| 735 | |
| 736 | @example |
| 737 | (@var{downcase} @var{upcase} @var{canonicalize} @var{equivalences}) |
| 738 | @end example |
| 739 | |
| 740 | @noindent |
| 741 | where each element is either @code{nil} or a string of length 256. The |
| 742 | element @var{downcase} says how to map each character to its lower-case |
| 743 | equivalent. The element @var{upcase} maps each character to its |
| 744 | upper-case equivalent. If lower and upper case characters are in |
| 745 | one-to-one correspondence, use @code{nil} for @var{upcase}; then Emacs |
| 746 | deduces the upcase table from @var{downcase}. |
| 747 | |
| 748 | For some languages, upper and lower case letters are not in one-to-one |
| 749 | correspondence. There may be two different lower case letters with the |
| 750 | same upper case equivalent. In these cases, you need to specify the |
| 751 | maps for both directions. |
| 752 | |
| 753 | The element @var{canonicalize} maps each character to a canonical |
| 754 | equivalent; any two characters that are related by case-conversion have |
| 755 | the same canonical equivalent character. |
| 756 | |
| 757 | The element @var{equivalences} is a map that cyclicly permutes each |
| 758 | equivalence class (of characters with the same canonical equivalent). |
| 759 | (For ordinary @sc{ASCII}, this would map @samp{a} into @samp{A} and |
| 760 | @samp{A} into @samp{a}, and likewise for each set of equivalent |
| 761 | characters.) |
| 762 | |
| 763 | When you construct a case table, you can provide @code{nil} for |
| 764 | @var{canonicalize}; then Emacs fills in this string from @var{upcase} |
| 765 | and @var{downcase}. You can also provide @code{nil} for |
| 766 | @var{equivalences}; then Emacs fills in this string from |
| 767 | @var{canonicalize}. In a case table that is actually in use, those |
| 768 | components are non-@code{nil}. Do not try to specify @var{equivalences} |
| 769 | without also specifying @var{canonicalize}. |
| 770 | |
| 771 | Each buffer has a case table. Emacs also has a @dfn{standard case |
| 772 | table} which is copied into each buffer when you create the buffer. |
| 773 | Changing the standard case table doesn't affect any existing buffers. |
| 774 | |
| 775 | Here are the functions for working with case tables: |
| 776 | |
| 777 | @defun case-table-p object |
| 778 | This predicate returns non-@code{nil} if @var{object} is a valid case |
| 779 | table. |
| 780 | @end defun |
| 781 | |
| 782 | @defun set-standard-case-table table |
| 783 | This function makes @var{table} the standard case table, so that it will |
| 784 | apply to any buffers created subsequently. |
| 785 | @end defun |
| 786 | |
| 787 | @defun standard-case-table |
| 788 | This returns the standard case table. |
| 789 | @end defun |
| 790 | |
| 791 | @defun current-case-table |
| 792 | This function returns the current buffer's case table. |
| 793 | @end defun |
| 794 | |
| 795 | @defun set-case-table table |
| 796 | This sets the current buffer's case table to @var{table}. |
| 797 | @end defun |
| 798 | |
| 799 | The following three functions are convenient subroutines for packages |
| 800 | that define non-@sc{ASCII} character sets. They modify a string |
| 801 | @var{downcase-table} provided as an argument; this should be a string to |
| 802 | be used as the @var{downcase} part of a case table. They also modify |
| 803 | the standard syntax table. @xref{Syntax Tables}. |
| 804 | |
| 805 | @defun set-case-syntax-pair uc lc downcase-table |
| 806 | This function specifies a pair of corresponding letters, one upper case |
| 807 | and one lower case. |
| 808 | @end defun |
| 809 | |
| 810 | @defun set-case-syntax-delims l r downcase-table |
| 811 | This function makes characters @var{l} and @var{r} a matching pair of |
| 812 | case-invariant delimiters. |
| 813 | @end defun |
| 814 | |
| 815 | @defun set-case-syntax char syntax downcase-table |
| 816 | This function makes @var{char} case-invariant, with syntax |
| 817 | @var{syntax}. |
| 818 | @end defun |
| 819 | |
| 820 | @deffn Command describe-buffer-case-table |
| 821 | This command displays a description of the contents of the current |
| 822 | buffer's case table. |
| 823 | @end deffn |
| 824 | |
| 825 | @cindex ISO Latin 1 |
| 826 | @pindex iso-syntax |
| 827 | You can load the library @file{iso-syntax} to set up the standard syntax |
| 828 | table and define a case table for the 8-bit ISO Latin 1 character set. |