2 @c This is part of the XEmacs Lisp Reference Manual.
3 @c Copyright (C) 1990, 1991, 1992, 1993, 1994 Free Software Foundation, Inc.
4 @c See the file lispref.texi for copying conditions.
5 @setfilename ../../info/strings.info
6 @node Strings and Characters, Lists, Numbers, Top
7 @chapter Strings and Characters
9 @cindex character arrays
13 A string in XEmacs Lisp is an array that contains an ordered sequence
14 of characters. Strings are used as names of symbols, buffers, and
15 files, to send messages to users, to hold text being copied between
16 buffers, and for many other purposes. Because strings are so important,
17 XEmacs Lisp has many functions expressly for manipulating them. XEmacs
18 Lisp programs use strings more often than individual characters.
21 * Basics: String Basics. Basic properties of strings and characters.
22 * Predicates for Strings:: Testing whether an object is a string or char.
23 * Creating Strings:: Functions to allocate new strings.
24 * Predicates for Characters:: Testing whether an object is a character.
25 * Character Codes:: Each character has an equivalent integer.
26 * Text Comparison:: Comparing characters or strings.
27 * String Conversion:: Converting characters or strings and vice versa.
28 * Modifying Strings:: Changing characters in a string.
29 * String Properties:: Additional information attached to strings.
30 * Formatting Strings:: @code{format}: XEmacs's analog of @code{printf}.
31 * Character Case:: Case conversion functions.
32 * Case Tables:: Customizing case conversion.
33 * Char Tables:: Mapping from characters to Lisp objects.
37 @section String and Character Basics
39 Strings in XEmacs Lisp are arrays that contain an ordered sequence of
40 characters. Characters are their own primitive object type in XEmacs
41 20. However, in XEmacs 19, characters are represented in XEmacs Lisp as
42 integers; whether an integer was intended as a character or not is
43 determined only by how it is used. @xref{Character Type}.
45 The length of a string (like any array) is fixed and independent of
46 the string contents, and cannot be altered. Strings in Lisp are
47 @emph{not} terminated by a distinguished character code. (By contrast,
48 strings in C are terminated by a character with @sc{ASCII} code 0.)
49 This means that any character, including the null character (@sc{ASCII}
50 code 0), is a valid element of a string.@refill
52 Since strings are considered arrays, you can operate on them with the
53 general array functions. (@xref{Sequences Arrays Vectors}.) For
54 example, you can access or change individual characters in a string
55 using the functions @code{aref} and @code{aset} (@pxref{Array
58 Strings use an efficient representation for storing the characters
59 in them, and thus take up much less memory than a vector of the same
62 Sometimes you will see strings used to hold key sequences. This
63 exists for backward compatibility with Emacs 18, but should @emph{not}
64 be used in new code, since many key chords can't be represented at
65 all and others (in particular meta key chords) are confused with
68 @ignore @c Not accurate any more
69 Each character in a string is stored in a single byte. Therefore,
70 numbers not in the range 0 to 255 are truncated when stored into a
71 string. This means that a string takes up much less memory than a
72 vector of the same length.
74 Sometimes key sequences are represented as strings. When a string is
75 a key sequence, string elements in the range 128 to 255 represent meta
76 characters (which are extremely large integers) rather than keyboard
77 events in the range 128 to 255.
79 Strings cannot hold characters that have the hyper, super or alt
80 modifiers; they can hold @sc{ASCII} control characters, but no other
81 control characters. They do not distinguish case in @sc{ASCII} control
82 characters. @xref{Character Type}, for more information about
83 representation of meta and other modifiers for keyboard input
87 Strings are useful for holding regular expressions. You can also
88 match regular expressions against strings (@pxref{Regexp Search}). The
89 functions @code{match-string} (@pxref{Simple Match Data}) and
90 @code{replace-match} (@pxref{Replacing Match}) are useful for
91 decomposing and modifying strings based on regular expression matching.
93 Like a buffer, a string can contain extents in it. These extents are
94 created when a function such as @code{buffer-substring} is called on a
95 region with duplicable extents in it. When the string is inserted into
96 a buffer, the extents are inserted along with it. @xref{Duplicable
99 @xref{Text}, for information about functions that display strings or
100 copy them into buffers. @xref{Character Type}, and @ref{String Type},
101 for information about the syntax of characters and strings.
103 @node Predicates for Strings
104 @section The Predicates for Strings
106 For more information about general sequence and array predicates,
107 see @ref{Sequences Arrays Vectors}, and @ref{Arrays}.
109 @defun stringp object
110 This function returns @code{t} if @var{object} is a string, @code{nil}
114 @defun char-or-string-p object
115 This function returns @code{t} if @var{object} is a string or a
116 character, @code{nil} otherwise.
118 In XEmacs addition, this function also returns @code{t} if @var{object}
119 is an integer that can be represented as a character. This is because
120 of compatibility with previous XEmacs and should not be depended on.
123 @node Creating Strings
124 @section Creating Strings
126 The following functions create strings, either from scratch, or by
127 putting strings together, or by taking them apart.
129 @defun string &rest characters
130 This function returns a new string made up of @var{characters}.
133 (string ?X ?E ?m ?a ?c ?s)
139 Analogous functions operating on other data types include @code{list},
140 @code{cons} (@pxref{Building Lists}), @code{vector} (@pxref{Vectors})
141 and @code{bit-vector} (@pxref{Bit Vectors}). This function has not been
142 available in XEmacs prior to 21.0 and FSF Emacs prior to 20.3.
145 @defun make-string count character
146 This function returns a string made up of @var{count} repetitions of
147 @var{character}. If @var{count} is negative, an error is signaled.
156 Other functions to compare with this one include @code{char-to-string}
157 (@pxref{String Conversion}), @code{make-vector} (@pxref{Vectors}), and
158 @code{make-list} (@pxref{Building Lists}).
161 @defun substring string start &optional end
162 This function returns a new string which consists of those characters
163 from @var{string} in the range from (and including) the character at the
164 index @var{start} up to (but excluding) the character at the index
165 @var{end}. The first character is at index zero.
169 (substring "abcdefg" 0 3)
175 Here the index for @samp{a} is 0, the index for @samp{b} is 1, and the
176 index for @samp{c} is 2. Thus, three letters, @samp{abc}, are copied
177 from the string @code{"abcdefg"}. The index 3 marks the character
178 position up to which the substring is copied. The character whose index
179 is 3 is actually the fourth character in the string.
181 A negative number counts from the end of the string, so that @minus{}1
182 signifies the index of the last character of the string. For example:
186 (substring "abcdefg" -3 -1)
192 In this example, the index for @samp{e} is @minus{}3, the index for
193 @samp{f} is @minus{}2, and the index for @samp{g} is @minus{}1.
194 Therefore, @samp{e} and @samp{f} are included, and @samp{g} is excluded.
196 When @code{nil} is used as an index, it stands for the length of the
201 (substring "abcdefg" -3 nil)
206 Omitting the argument @var{end} is equivalent to specifying @code{nil}.
207 It follows that @code{(substring @var{string} 0)} returns a copy of all
212 (substring "abcdefg" 0)
218 But we recommend @code{copy-sequence} for this purpose (@pxref{Sequence
221 If the characters copied from @var{string} have duplicable extents or
222 text properties, those are copied into the new string also.
223 @xref{Duplicable Extents}.
225 A @code{wrong-type-argument} error is signaled if either @var{start} or
226 @var{end} is not an integer or @code{nil}. An @code{args-out-of-range}
227 error is signaled if @var{start} indicates a character following
228 @var{end}, or if either integer is out of range for @var{string}.
230 Contrast this function with @code{buffer-substring} (@pxref{Buffer
231 Contents}), which returns a string containing a portion of the text in
232 the current buffer. The beginning of a string is at index 0, but the
233 beginning of a buffer is at index 1.
236 @defun concat &rest sequences
237 @cindex copying strings
238 @cindex concatenating strings
239 This function returns a new string consisting of the characters in the
240 arguments passed to it (along with their text properties, if any). The
241 arguments may be strings, lists of numbers, or vectors of numbers; they
242 are not themselves changed. If @code{concat} receives no arguments, it
243 returns an empty string.
246 (concat "abc" "-def")
248 (concat "abc" (list 120 (+ 256 121)) [122])
250 ;; @r{@code{nil} is an empty sequence.}
251 (concat "abc" nil "-def")
253 (concat "The " "quick brown " "fox.")
254 @result{} "The quick brown fox."
260 The second example above shows how characters stored in strings are
261 taken modulo 256. In other words, each character in the string is
264 The @code{concat} function always constructs a new string that is
265 not @code{eq} to any existing string.
267 When an argument is an integer (not a sequence of integers), it is
268 converted to a string of digits making up the decimal printed
269 representation of the integer. @strong{Don't use this feature; we plan
270 to eliminate it. If you already use this feature, change your programs
271 now!} The proper way to convert an integer to a decimal number in this
272 way is with @code{format} (@pxref{Formatting Strings}) or
273 @code{number-to-string} (@pxref{String Conversion}).
284 For information about other concatenation functions, see the description
285 of @code{mapconcat} in @ref{Mapping Functions}, @code{vconcat} in
286 @ref{Vectors}, @code{bvconcat} in @ref{Bit Vectors}, and @code{append}
287 in @ref{Building Lists}.
290 @node Predicates for Characters
291 @section The Predicates for Characters
293 @defun characterp object
294 This function returns @code{t} if @var{object} is a character.
296 Some functions that work on integers (e.g. the comparison functions
297 <, <=, =, /=, etc. and the arithmetic functions +, -, *, etc.)
298 accept characters and implicitly convert them into integers. In
299 general, functions that work on characters also accept char-ints and
300 implicitly convert them into characters. WARNING: Neither of these
301 behaviors is very desirable, and they are maintained for backward
302 compatibility with old E-Lisp programs that confounded characters and
303 integers willy-nilly. These behaviors may change in the future; therefore,
304 do not rely on them. Instead, convert the characters explicitly
305 using @code{char-int}.
308 @defun integer-or-char-p object
309 This function returns @code{t} if @var{object} is an integer or character.
312 @node Character Codes
313 @section Character Codes
316 This function converts a character into an equivalent integer.
317 The resulting integer will always be non-negative. The integers in
318 the range 0 - 255 map to characters as follows:
328 Right half of ISO-8859-1
331 If support for @sc{MULE} does not exist, these are the only valid
332 character values. When @sc{MULE} support exists, the values assigned to
333 other characters may vary depending on the particular version of XEmacs,
334 the order in which character sets were loaded, etc., and you should not
338 @defun int-char integer
339 This function converts an integer into the equivalent character. Not
340 all integers correspond to valid characters; use @code{char-int-p} to
341 determine whether this is the case. If the integer cannot be converted,
342 @code{nil} is returned.
345 @defun char-int-p object
346 This function returns @code{t} if @var{object} is an integer that can be
347 converted into a character.
350 @defun char-or-char-int-p object
351 This function returns @code{t} if @var{object} is a character or an
352 integer that can be converted into one.
356 @node Text Comparison
357 @section Comparison of Characters and Strings
358 @cindex string equality
360 @defun char-equal character1 character2
361 This function returns @code{t} if the arguments represent the same
362 character, @code{nil} otherwise. This function ignores differences
363 in case if @code{case-fold-search} is non-@code{nil}.
368 (let ((case-fold-search t))
371 (let ((case-fold-search nil))
377 @defun char= character1 character2
378 This function returns @code{t} if the arguments represent the same
379 character, @code{nil} otherwise. Case is significant.
386 (let ((case-fold-search t))
389 (let ((case-fold-search nil))
395 @defun string= string1 string2
396 This function returns @code{t} if the characters of the two strings
397 match exactly; case is significant.
400 (string= "abc" "abc")
402 (string= "abc" "ABC")
408 @ignore @c `equal' in XEmacs does not compare text properties
409 The function @code{string=} ignores the text properties of the
410 two strings. To compare strings in a way that compares their text
411 properties also, use @code{equal} (@pxref{Equality Predicates}).
415 @defun string-equal string1 string2
416 @code{string-equal} is another name for @code{string=}.
419 @cindex lexical comparison
420 @defun string< string1 string2
421 @c (findex string< causes problems for permuted index!!)
422 This function compares two strings a character at a time. First it
423 scans both the strings at once to find the first pair of corresponding
424 characters that do not match. If the lesser character of those two is
425 the character from @var{string1}, then @var{string1} is less, and this
426 function returns @code{t}. If the lesser character is the one from
427 @var{string2}, then @var{string1} is greater, and this function returns
428 @code{nil}. If the two strings match entirely, the value is @code{nil}.
430 Pairs of characters are compared by their @sc{ASCII} codes. Keep in
431 mind that lower case letters have higher numeric values in the
432 @sc{ASCII} character set than their upper case counterparts; numbers and
433 many punctuation characters have a lower numeric value than upper case
438 (string< "abc" "abd")
440 (string< "abd" "abc")
442 (string< "123" "abc")
447 When the strings have different lengths, and they match up to the
448 length of @var{string1}, then the result is @code{t}. If they match up
449 to the length of @var{string2}, the result is @code{nil}. A string of
450 no characters is less than any other string.
468 @defun string-lessp string1 string2
469 @code{string-lessp} is another name for @code{string<}.
472 See also @code{compare-buffer-substrings} in @ref{Comparing Text}, for
473 a way to compare text in buffers. The function @code{string-match},
474 which matches a regular expression against a string, can be used
475 for a kind of string comparison; see @ref{Regexp Search}.
477 @node String Conversion
478 @section Conversion of Characters and Strings
479 @cindex conversion of strings
481 This section describes functions for conversions between characters,
482 strings and integers. @code{format} and @code{prin1-to-string}
483 (@pxref{Output Functions}) can also convert Lisp objects into strings.
484 @code{read-from-string} (@pxref{Input Functions}) can ``convert'' a
485 string representation of a Lisp object into an object.
487 @xref{Documentation}, for functions that produce textual descriptions
488 of text characters and general input events
489 (@code{single-key-description} and @code{text-char-description}). These
490 functions are used primarily for making help messages.
492 @defun char-to-string character
493 @cindex character to string
494 This function returns a new string with a length of one character.
495 The value of @var{character}, modulo 256, is used to initialize the
496 element of the string.
498 This function is similar to @code{make-string} with an integer argument
499 of 1. (@xref{Creating Strings}.) This conversion can also be done with
500 @code{format} using the @samp{%c} format specification.
501 (@xref{Formatting Strings}.)
506 (char-to-string (+ 256 ?x))
513 @defun string-to-char string
514 @cindex string to character
515 This function returns the first character in @var{string}. If the
516 string is empty, the function returns 0. (Under XEmacs 19, the value is
517 also 0 when the first character of @var{string} is the null character,
521 (string-to-char "ABC")
522 @result{} ?A ;; @r{Under XEmacs 20.}
523 @result{} 65 ;; @r{Under XEmacs 19.}
524 (string-to-char "xyz")
525 @result{} ?x ;; @r{Under XEmacs 20.}
526 @result{} 120 ;; @r{Under XEmacs 19.}
529 (string-to-char "\000")
530 @result{} ?\^@ ;; @r{Under XEmacs 20.}
531 @result{} 0 ;; @r{Under XEmacs 20.}
534 This function may be eliminated in the future if it does not seem useful
538 @defun number-to-string number
539 @cindex integer to string
540 @cindex integer to decimal
541 This function returns a string consisting of the printed
542 representation of @var{number}, which may be an integer or a floating
543 point number. The value starts with a sign if the argument is
547 (number-to-string 256)
549 (number-to-string -23)
551 (number-to-string -23.5)
555 @cindex int-to-string
556 @code{int-to-string} is a semi-obsolete alias for this function.
558 See also the function @code{format} in @ref{Formatting Strings}.
561 @defun string-to-number string &optional base
562 @cindex string to number
563 This function returns the numeric value of the characters in
564 @var{string}, read in @var{base}. It skips spaces and tabs at the
565 beginning of @var{string}, then reads as much of @var{string} as it can
566 interpret as a number. (On some systems it ignores other whitespace at
567 the beginning, not just spaces and tabs.) If the first character after
568 the ignored whitespace is not a digit or a minus sign, this function
571 If @var{base} is not specified, it defaults to ten. With @var{base}
572 other than ten, only integers can be read.
575 (string-to-number "256")
577 (string-to-number "25 is a perfect square.")
579 (string-to-number "X256")
581 (string-to-number "-4.5")
583 (string-to-number "ffff" 16)
587 @findex string-to-int
588 @code{string-to-int} is an obsolete alias for this function.
591 @node Modifying Strings
592 @section Modifying Strings
593 @cindex strings, modifying
595 You can modify a string using the general array-modifying primitives.
596 @xref{Arrays}. The function @code{aset} modifies a single character;
597 the function @code{fillarray} sets all characters in the string to
598 a specified character.
600 Each string has a tick counter that starts out at zero (when the string
601 is created) and is incremented each time a change is made to that
604 @defun string-modified-tick string
605 This function returns the tick counter for @samp{string}.
608 @node String Properties
609 @section String Properties
610 @cindex string properties
611 @cindex properties of strings
613 Similar to symbols, extents, faces, and glyphs, you can attach
614 additional information to strings in the form of @dfn{string
615 properties}. These differ from text properties, which are logically
616 attached to particular characters in the string.
618 To attach a property to a string, use @code{put}. To retrieve a property
619 from a string, use @code{get}. You can also use @code{remprop} to remove
620 a property from a string and @code{object-props} to retrieve a list of
621 all the properties in a string.
623 @node Formatting Strings
624 @section Formatting Strings
625 @cindex formatting strings
626 @cindex strings, formatting them
628 @dfn{Formatting} means constructing a string by substitution of
629 computed values at various places in a constant string. This string
630 controls how the other values are printed as well as where they appear;
631 it is called a @dfn{format string}.
633 Formatting is often useful for computing messages to be displayed. In
634 fact, the functions @code{message} and @code{error} provide the same
635 formatting feature described here; they differ from @code{format} only
636 in how they use the result of formatting.
638 @defun format string &rest objects
639 This function returns a new string that is made by copying
640 @var{string} and then replacing any format specification
641 in the copy with encodings of the corresponding @var{objects}. The
642 arguments @var{objects} are the computed values to be formatted.
645 @cindex @samp{%} in format
646 @cindex format specification
647 A format specification is a sequence of characters beginning with a
648 @samp{%}. Thus, if there is a @samp{%d} in @var{string}, the
649 @code{format} function replaces it with the printed representation of
650 one of the values to be formatted (one of the arguments @var{objects}).
655 (format "The value of fill-column is %d." fill-column)
656 @result{} "The value of fill-column is 72."
660 If @var{string} contains more than one format specification, the
661 format specifications correspond with successive values from
662 @var{objects}. Thus, the first format specification in @var{string}
663 uses the first such value, the second format specification uses the
664 second such value, and so on. Any extra format specifications (those
665 for which there are no corresponding values) cause unpredictable
666 behavior. Any extra values to be formatted are ignored.
668 Certain format specifications require values of particular types.
669 However, no error is signaled if the value actually supplied fails to
670 have the expected type. Instead, the output is likely to be
673 Here is a table of valid format specifications:
677 Replace the specification with the printed representation of the object,
678 made without quoting. Thus, strings are represented by their contents
679 alone, with no @samp{"} characters, and symbols appear without @samp{\}
680 characters. This is equivalent to printing the object with @code{princ}.
682 If there is no corresponding object, the empty string is used.
685 Replace the specification with the printed representation of the object,
686 made with quoting. Thus, strings are enclosed in @samp{"} characters,
687 and @samp{\} characters appear where necessary before special characters.
688 This is equivalent to printing the object with @code{prin1}.
690 If there is no corresponding object, the empty string is used.
693 @cindex integer to octal
694 Replace the specification with the base-eight representation of an
699 Replace the specification with the base-ten representation of an
703 @cindex integer to hexadecimal
704 Replace the specification with the base-sixteen representation of an
705 integer, using lowercase letters.
708 @cindex integer to hexadecimal
709 Replace the specification with the base-sixteen representation of an
710 integer, using uppercase letters.
713 Replace the specification with the character which is the value given.
716 Replace the specification with the exponential notation for a floating
717 point number (e.g. @samp{7.85200e+03}).
720 Replace the specification with the decimal-point notation for a floating
724 Replace the specification with notation for a floating point number,
725 using a ``pretty format''. Either exponential notation or decimal-point
726 notation will be used (usually whichever is shorter), and trailing
727 zeroes are removed from the fractional part.
730 A single @samp{%} is placed in the string. This format specification is
731 unusual in that it does not use a value. For example, @code{(format "%%
732 %d" 30)} returns @code{"% 30"}.
735 Any other format character results in an @samp{Invalid format
738 Here are several examples:
742 (format "The name of this buffer is %s." (buffer-name))
743 @result{} "The name of this buffer is strings.texi."
745 (format "The buffer object prints as %s." (current-buffer))
746 @result{} "The buffer object prints as #<buffer strings.texi>."
748 (format "The octal value of %d is %o,
749 and the hex value is %x." 18 18 18)
750 @result{} "The octal value of 18 is 22,
751 and the hex value is 12."
755 There are many additional flags and specifications that can occur
756 between the @samp{%} and the format character, in the following order:
760 An optional repositioning specification, which is a positive
761 integer followed by a @samp{$}.
764 Zero or more of the optional flag characters @samp{-}, @samp{+},
765 @samp{ }, @samp{0}, and @samp{#}.
768 An asterisk (@samp{*}, meaning that the field width is now assumed to
769 have been specified as an argument.
772 An optional minimum field width.
775 An optional precision, preceded by a @samp{.} character.
778 @cindex repositioning format arguments
779 @cindex multilingual string formatting
780 A @dfn{repositioning} specification changes which argument to
781 @code{format} is used by the current and all following format
782 specifications. Normally the first specification uses the first
783 argument, the second specification uses the second argument, etc. Using
784 a repositioning specification, you can change this. By placing a number
785 @var{N} followed by a @samp{$} between the @samp{%} and the format
786 character, you cause the specification to use the @var{N}th argument.
787 The next specification will use the @var{N}+1'th argument, etc.
793 (format "Can't find file `%s' in directory `%s'."
794 "ignatius.c" "loyola/")
795 @result{} "Can't find file `ignatius.c' in directory `loyola/'."
797 (format "In directory `%2$s', the file `%1$s' was not found."
798 "ignatius.c" "loyola/")
799 @result{} "In directory `loyola/', the file `ignatius.c' was not found."
802 "The numbers %d and %d are %1$x and %x in hex and %1$o and %o in octal."
804 @result{} "The numbers 37 and 12 are 25 and c in hex and 45 and 14 in octal."
808 As you can see, this lets you reprocess arguments more than once or
809 reword a format specification (thereby moving the arguments around)
810 without having to actually reorder the arguments. This is especially
811 useful in translating messages from one language to another: Different
812 languages use different word orders, and this sometimes entails changing
813 the order of the arguments. By using repositioning specifications,
814 this can be accomplished without having to embed knowledge of particular
815 languages into the location in the program's code where the message is
818 @cindex numeric prefix
821 All the specification characters allow an optional numeric prefix
822 between the @samp{%} and the character, and following any repositioning
823 specification or flag. The optional numeric prefix defines the minimum
824 width for the object. If the printed representation of the object
825 contains fewer characters than this, then it is padded. The padding is
826 normally on the left, but will be on the right if the @samp{-} flag
827 character is given. The padding character is normally a space, but if
828 the @samp{0} flag character is given, zeros are used for padding.
831 (format "%06d is padded on the left with zeros" 123)
832 @result{} "000123 is padded on the left with zeros"
834 (format "%-6d is padded on the right" 123)
835 @result{} "123 is padded on the right"
838 @code{format} never truncates an object's printed representation, no
839 matter what width you specify. Thus, you can use a numeric prefix to
840 specify a minimum spacing between columns with no risk of losing
843 In the following three examples, @samp{%7s} specifies a minimum width
844 of 7. In the first case, the string inserted in place of @samp{%7s} has
845 only 3 letters, so 4 blank spaces are inserted for padding. In the
846 second case, the string @code{"specification"} is 13 letters wide but is
847 not truncated. In the third case, the padding is on the right.
851 (format "The word `%7s' actually has %d letters in it."
852 "foo" (length "foo"))
853 @result{} "The word ` foo' actually has 3 letters in it."
857 (format "The word `%7s' actually has %d letters in it."
858 "specification" (length "specification"))
859 @result{} "The word `specification' actually has 13 letters in it."
863 (format "The word `%-7s' actually has %d letters in it."
864 "foo" (length "foo"))
865 @result{} "The word `foo ' actually has 3 letters in it."
869 @cindex format precision
870 @cindex precision of formatted numbers
871 After any minimum field width, a precision may be specified by
872 preceding it with a @samp{.} character. The precision specifies the
873 minimum number of digits to appear in @samp{%d}, @samp{%i}, @samp{%o},
874 @samp{%x}, and @samp{%X} conversions (the number is padded on the left
875 with zeroes as necessary); the number of digits printed after the
876 decimal point for @samp{%f}, @samp{%e}, and @samp{%E} conversions; the
877 number of significant digits printed in @samp{%g} and @samp{%G}
878 conversions; and the maximum number of non-padding characters printed in
879 @samp{%s} and @samp{%S} conversions. The default precision for
880 floating-point conversions is six.
882 The other flag characters have the following meanings:
886 The @samp{ } flag means prefix non-negative numbers with a space.
889 The @samp{+} flag means prefix non-negative numbers with a plus sign.
892 The @samp{#} flag means print numbers in an alternate, more verbose
893 format: octal numbers begin with zero; hex numbers begin with a
894 @samp{0x} or @samp{0X}; a decimal point is printed in @samp{%f},
895 @samp{%e}, and @samp{%E} conversions even if no numbers are printed
896 after it; and trailing zeroes are not omitted in @samp{%g} and @samp{%G}
901 @section Character Case
904 @cindex character case
906 The character case functions change the case of single characters or
907 of the contents of strings. The functions convert only alphabetic
908 characters (the letters @samp{A} through @samp{Z} and @samp{a} through
909 @samp{z}); other characters are not altered. The functions do not
910 modify the strings that are passed to them as arguments.
912 The examples below use the characters @samp{X} and @samp{x} which have
913 @sc{ASCII} codes 88 and 120 respectively.
915 @defun downcase string-or-char
916 This function converts a character or a string to lower case.
918 When the argument to @code{downcase} is a string, the function creates
919 and returns a new string in which each letter in the argument that is
920 upper case is converted to lower case. When the argument to
921 @code{downcase} is a character, @code{downcase} returns the
922 corresponding lower case character. (This value is actually an integer
923 under XEmacs 19.) If the original character is lower case, or is not a
924 letter, then the value equals the original character.
927 (downcase "The cat in the hat")
928 @result{} "the cat in the hat"
931 @result{} ?x ;; @r{Under XEmacs 20.}
932 @result{} 120 ;; @r{Under XEmacs 19.}
937 @defun upcase string-or-char
938 This function converts a character or a string to upper case.
940 When the argument to @code{upcase} is a string, the function creates
941 and returns a new string in which each letter in the argument that is
942 lower case is converted to upper case.
944 When the argument to @code{upcase} is a character, @code{upcase} returns
945 the corresponding upper case character. (This value is actually an
946 integer under XEmacs 19.) If the original character is upper case, or
947 is not a letter, then the value equals the original character.
950 (upcase "The cat in the hat")
951 @result{} "THE CAT IN THE HAT"
954 @result{} ?X ;; @r{Under XEmacs 20.}
955 @result{} 88 ;; @r{Under XEmacs 19.}
959 @defun capitalize string-or-char
960 @cindex capitalization
961 This function capitalizes strings or characters. If
962 @var{string-or-char} is a string, the function creates and returns a new
963 string, whose contents are a copy of @var{string-or-char} in which each
964 word has been capitalized. This means that the first character of each
965 word is converted to upper case, and the rest are converted to lower
968 The definition of a word is any sequence of consecutive characters that
969 are assigned to the word constituent syntax class in the current syntax
970 table (@pxref{Syntax Class Table}).
972 When the argument to @code{capitalize} is a character, @code{capitalize}
973 has the same result as @code{upcase}.
976 (capitalize "The cat in the hat")
977 @result{} "The Cat In The Hat"
979 (capitalize "THE 77TH-HATTED CAT")
980 @result{} "The 77th-Hatted Cat"
984 @result{} ?X ;; @r{Under XEmacs 20.}
985 @result{} 88 ;; @r{Under XEmacs 19.}
991 @section The Case Table
993 You can customize case conversion by installing a special @dfn{case
994 table}. A case table specifies the mapping between upper case and lower
995 case letters. It affects both the string and character case conversion
996 functions (see the previous section) and those that apply to text in the
997 buffer (@pxref{Case Changes}). You need a case table if you are using a
998 language which has letters other than the standard @sc{ASCII} letters.
1000 A case table is a list of this form:
1003 (@var{downcase} @var{upcase} @var{canonicalize} @var{equivalences})
1007 where each element is either @code{nil} or a string of length 256. The
1008 element @var{downcase} says how to map each character to its lower-case
1009 equivalent. The element @var{upcase} maps each character to its
1010 upper-case equivalent. If lower and upper case characters are in
1011 one-to-one correspondence, use @code{nil} for @var{upcase}; then XEmacs
1012 deduces the upcase table from @var{downcase}.
1014 For some languages, upper and lower case letters are not in one-to-one
1015 correspondence. There may be two different lower case letters with the
1016 same upper case equivalent. In these cases, you need to specify the
1017 maps for both directions.
1019 The element @var{canonicalize} maps each character to a canonical
1020 equivalent; any two characters that are related by case-conversion have
1021 the same canonical equivalent character.
1023 The element @var{equivalences} is a map that cyclicly permutes each
1024 equivalence class (of characters with the same canonical equivalent).
1025 (For ordinary @sc{ASCII}, this would map @samp{a} into @samp{A} and
1026 @samp{A} into @samp{a}, and likewise for each set of equivalent
1029 When you construct a case table, you can provide @code{nil} for
1030 @var{canonicalize}; then Emacs fills in this string from @var{upcase}
1031 and @var{downcase}. You can also provide @code{nil} for
1032 @var{equivalences}; then Emacs fills in this string from
1033 @var{canonicalize}. In a case table that is actually in use, those
1034 components are non-@code{nil}. Do not try to specify @var{equivalences}
1035 without also specifying @var{canonicalize}.
1037 Each buffer has a case table. XEmacs also has a @dfn{standard case
1038 table} which is copied into each buffer when you create the buffer.
1039 Changing the standard case table doesn't affect any existing buffers.
1041 Here are the functions for working with case tables:
1043 @defun case-table-p object
1044 This predicate returns non-@code{nil} if @var{object} is a valid case
1048 @defun set-standard-case-table table
1049 This function makes @var{table} the standard case table, so that it will
1050 apply to any buffers created subsequently.
1053 @defun standard-case-table
1054 This returns the standard case table.
1057 @defun current-case-table
1058 This function returns the current buffer's case table.
1061 @defun set-case-table table
1062 This sets the current buffer's case table to @var{table}.
1065 The following three functions are convenient subroutines for packages
1066 that define non-@sc{ASCII} character sets. They modify a string
1067 @var{downcase-table} provided as an argument; this should be a string to
1068 be used as the @var{downcase} part of a case table. They also modify
1069 the standard syntax table. @xref{Syntax Tables}.
1071 @defun set-case-syntax-pair uc lc downcase-table
1072 This function specifies a pair of corresponding letters, one upper case
1076 @defun set-case-syntax-delims l r downcase-table
1077 This function makes characters @var{l} and @var{r} a matching pair of
1078 case-invariant delimiters.
1081 @defun set-case-syntax char syntax downcase-table
1082 This function makes @var{char} case-invariant, with syntax
1086 @deffn Command describe-buffer-case-table
1087 This command displays a description of the contents of the current
1088 buffer's case table.
1093 You can load the library @file{iso-syntax} to set up the standard syntax
1094 table and define a case table for the 8-bit ISO Latin 1 character set.
1097 @section The Char Table
1099 A char table is a table that maps characters (or ranges of characters)
1100 to values. Char tables are specialized for characters, only allowing
1101 particular sorts of ranges to be assigned values. Although this
1102 loses in generality, it makes for extremely fast (constant-time)
1103 lookups, and thus is feasible for applications that do an extremely
1104 large number of lookups (e.g. scanning a buffer for a character in
1105 a particular syntax, where a lookup in the syntax table must occur
1106 once per character).
1108 Note that char tables as a primitive type, and all of the functions in
1109 this section, exist only in XEmacs 20. In XEmacs 19, char tables are
1110 generally implemented using a vector of 256 elements.
1112 When @sc{MULE} support exists, the types of ranges that can be assigned
1121 a single row in a two-octet charset
1126 When @sc{MULE} support is not present, the types of ranges that can be
1136 @defun char-table-p object
1137 This function returns non-@code{nil} if @var{object} is a char table.
1141 * Char Table Types:: Char tables have different uses.
1142 * Working With Char Tables:: Creating and working with char tables.
1145 @node Char Table Types
1146 @subsection Char Table Types
1148 Each char table type is used for a different purpose and allows different
1149 sorts of values. The different char table types are
1153 Used for category tables, which specify the regexp categories
1154 that a character is in. The valid values are @code{nil} or a
1155 bit vector of 95 elements. Higher-level Lisp functions are
1156 provided for working with category tables. Currently categories
1157 and category tables only exist when @sc{MULE} support is present.
1159 A generalized char table, for mapping from one character to
1160 another. Used for case tables, syntax matching tables,
1161 @code{keyboard-translate-table}, etc. The valid values are characters.
1163 An even more generalized char table, for mapping from a
1164 character to anything.
1166 Used for display tables, which specify how a particular character
1167 is to appear when displayed. #### Not yet implemented.
1169 Used for syntax tables, which specify the syntax of a particular
1170 character. Higher-level Lisp functions are provided for
1171 working with syntax tables. The valid values are integers.
1174 @defun char-table-type table
1175 This function returns the type of char table @var{table}.
1178 @defun char-table-type-list
1179 This function returns a list of the recognized char table types.
1182 @defun valid-char-table-type-p type
1183 This function returns @code{t} if @var{type} if a recognized char table type.
1186 @node Working With Char Tables
1187 @subsection Working With Char Tables
1189 @defun make-char-table type
1190 This function makes a new, empty char table of type @var{type}.
1191 @var{type} should be a symbol, one of @code{char}, @code{category},
1192 @code{display}, @code{generic}, or @code{syntax}.
1195 @defun put-char-table range val table
1196 This function sets the value for chars in @var{range} to be @var{val} in
1199 @var{range} specifies one or more characters to be affected and should be
1200 one of the following:
1204 @code{t} (all characters are affected)
1206 A charset (only allowed when @sc{MULE} support is present)
1208 A vector of two elements: a two-octet charset and a row number
1209 (only allowed when @sc{MULE} support is present)
1214 @var{val} must be a value appropriate for the type of @var{table}.
1217 @defun get-char-table ch table
1218 This function finds the value for char @var{ch} in @var{table}.
1221 @defun get-range-char-table range table &optional multi
1222 This function finds the value for a range in @var{table}. If there is
1223 more than one value, @var{multi} is returned (defaults to @code{nil}).
1226 @defun reset-char-table table
1227 This function resets a char table to its default state.
1230 @defun map-char-table function table &optional range
1231 This function maps @var{function} over entries in @var{table}, calling
1232 it with two args, each key and value in the table.
1234 @var{range} specifies a subrange to map over and is in the same format
1235 as the @var{range} argument to @code{put-range-table}. If omitted or
1236 @code{t}, it defaults to the entire table.
1239 @defun valid-char-table-value-p value char-table-type
1240 This function returns non-@code{nil} if @var{value} is a valid value for
1241 @var{char-table-type}.
1244 @defun check-valid-char-table-value value char-table-type
1245 This function signals an error if @var{value} is not a valid value for
1246 @var{char-table-type}.