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diff man/lispref/strings.texi @ 0:376386a54a3c r19-14
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date | Mon, 13 Aug 2007 08:45:50 +0200 |
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--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/man/lispref/strings.texi Mon Aug 13 08:45:50 2007 +0200 @@ -0,0 +1,1198 @@ +@c -*-texinfo-*- +@c This is part of the XEmacs Lisp Reference Manual. +@c Copyright (C) 1990, 1991, 1992, 1993, 1994 Free Software Foundation, Inc. +@c See the file lispref.texi for copying conditions. +@setfilename ../../info/strings.info +@node Strings and Characters, Lists, Numbers, Top +@chapter Strings and Characters +@cindex strings +@cindex character arrays +@cindex characters +@cindex bytes + + A string in XEmacs Lisp is an array that contains an ordered sequence +of characters. Strings are used as names of symbols, buffers, and +files, to send messages to users, to hold text being copied between +buffers, and for many other purposes. Because strings are so important, +XEmacs Lisp has many functions expressly for manipulating them. XEmacs +Lisp programs use strings more often than individual characters. + +@menu +* Basics: String Basics. Basic properties of strings and characters. +* Predicates for Strings:: Testing whether an object is a string or char. +* Creating Strings:: Functions to allocate new strings. +* Predicates for Characters:: Testing whether an object is a character. +* Character Codes:: Each character has an equivalent integer. +* Text Comparison:: Comparing characters or strings. +* String Conversion:: Converting characters or strings and vice versa. +* Modifying Strings:: Changing characters in a string. +* String Properties:: Additional information attached to strings. +* Formatting Strings:: @code{format}: XEmacs's analog of @code{printf}. +* Character Case:: Case conversion functions. +* Case Tables:: Customizing case conversion. +* Char Tables:: Mapping from characters to Lisp objects. +@end menu + +@node String Basics +@section String and Character Basics + + Strings in XEmacs Lisp are arrays that contain an ordered sequence of +characters. Characters are their own primitive object type in XEmacs +20. However, in XEmacs 19, characters are represented in XEmacs Lisp as +integers; whether an integer was intended as a character or not is +determined only by how it is used. @xref{Character Type}. + + The length of a string (like any array) is fixed and independent of +the string contents, and cannot be altered. Strings in Lisp are +@emph{not} terminated by a distinguished character code. (By contrast, +strings in C are terminated by a character with @sc{ASCII} code 0.) +This means that any character, including the null character (@sc{ASCII} +code 0), is a valid element of a string.@refill + + Since strings are considered arrays, you can operate on them with the +general array functions. (@xref{Sequences Arrays Vectors}.) For +example, you can access or change individual characters in a string +using the functions @code{aref} and @code{aset} (@pxref{Array +Functions}). + + Strings use an efficient representation for storing the characters +in them, and thus take up much less memory than a vector of the same +length. + + Sometimes you will see strings used to hold key sequences. This +exists for backward compatibility with Emacs 18, but should @emph{not} +be used in new code, since many key chords can't be represented at +all and others (in particular meta key chords) are confused with +accented characters. + +@ignore @c Not accurate any more + Each character in a string is stored in a single byte. Therefore, +numbers not in the range 0 to 255 are truncated when stored into a +string. This means that a string takes up much less memory than a +vector of the same length. + + Sometimes key sequences are represented as strings. When a string is +a key sequence, string elements in the range 128 to 255 represent meta +characters (which are extremely large integers) rather than keyboard +events in the range 128 to 255. + + Strings cannot hold characters that have the hyper, super or alt +modifiers; they can hold @sc{ASCII} control characters, but no other +control characters. They do not distinguish case in @sc{ASCII} control +characters. @xref{Character Type}, for more information about +representation of meta and other modifiers for keyboard input +characters. +@end ignore + + Strings are useful for holding regular expressions. You can also +match regular expressions against strings (@pxref{Regexp Search}). The +functions @code{match-string} (@pxref{Simple Match Data}) and +@code{replace-match} (@pxref{Replacing Match}) are useful for +decomposing and modifying strings based on regular expression matching. + + Like a buffer, a string can contain extents in it. These extents are +created when a function such as @code{buffer-substring} is called on a +region with duplicable extents in it. When the string is inserted into +a buffer, the extents are inserted along with it. @xref{Duplicable +Extents}. + + @xref{Text}, for information about functions that display strings or +copy them into buffers. @xref{Character Type}, and @ref{String Type}, +for information about the syntax of characters and strings. + +@node Predicates for Strings +@section The Predicates for Strings + +For more information about general sequence and array predicates, +see @ref{Sequences Arrays Vectors}, and @ref{Arrays}. + +@defun stringp object + This function returns @code{t} if @var{object} is a string, @code{nil} +otherwise. +@end defun + +@defun char-or-string-p object + This function returns @code{t} if @var{object} is a string or a +character, @code{nil} otherwise. +@end defun + +@node Creating Strings +@section Creating Strings + + The following functions create strings, either from scratch, or by +putting strings together, or by taking them apart. + +@defun make-string count character + This function returns a string made up of @var{count} repetitions of +@var{character}. If @var{count} is negative, an error is signaled. + +@example +(make-string 5 ?x) + @result{} "xxxxx" +(make-string 0 ?x) + @result{} "" +@end example + + Other functions to compare with this one include @code{char-to-string} +(@pxref{String Conversion}), @code{make-vector} (@pxref{Vectors}), and +@code{make-list} (@pxref{Building Lists}). +@end defun + +@defun substring string start &optional end +This function returns a new string which consists of those characters +from @var{string} in the range from (and including) the character at the +index @var{start} up to (but excluding) the character at the index +@var{end}. The first character is at index zero. + +@example +@group +(substring "abcdefg" 0 3) + @result{} "abc" +@end group +@end example + +@noindent +Here the index for @samp{a} is 0, the index for @samp{b} is 1, and the +index for @samp{c} is 2. Thus, three letters, @samp{abc}, are copied +from the string @code{"abcdefg"}. The index 3 marks the character +position up to which the substring is copied. The character whose index +is 3 is actually the fourth character in the string. + +A negative number counts from the end of the string, so that @minus{}1 +signifies the index of the last character of the string. For example: + +@example +@group +(substring "abcdefg" -3 -1) + @result{} "ef" +@end group +@end example + +@noindent +In this example, the index for @samp{e} is @minus{}3, the index for +@samp{f} is @minus{}2, and the index for @samp{g} is @minus{}1. +Therefore, @samp{e} and @samp{f} are included, and @samp{g} is excluded. + +When @code{nil} is used as an index, it stands for the length of the +string. Thus, + +@example +@group +(substring "abcdefg" -3 nil) + @result{} "efg" +@end group +@end example + +Omitting the argument @var{end} is equivalent to specifying @code{nil}. +It follows that @code{(substring @var{string} 0)} returns a copy of all +of @var{string}. + +@example +@group +(substring "abcdefg" 0) + @result{} "abcdefg" +@end group +@end example + +@noindent +But we recommend @code{copy-sequence} for this purpose (@pxref{Sequence +Functions}). + +If the characters copied from @var{string} have duplicable extents or +text properties, those are copied into the new string also. +@xref{Duplicable Extents}. + +A @code{wrong-type-argument} error is signaled if either @var{start} or +@var{end} is not an integer or @code{nil}. An @code{args-out-of-range} +error is signaled if @var{start} indicates a character following +@var{end}, or if either integer is out of range for @var{string}. + +Contrast this function with @code{buffer-substring} (@pxref{Buffer +Contents}), which returns a string containing a portion of the text in +the current buffer. The beginning of a string is at index 0, but the +beginning of a buffer is at index 1. +@end defun + +@defun concat &rest sequences +@cindex copying strings +@cindex concatenating strings +This function returns a new string consisting of the characters in the +arguments passed to it (along with their text properties, if any). The +arguments may be strings, lists of numbers, or vectors of numbers; they +are not themselves changed. If @code{concat} receives no arguments, it +returns an empty string. + +@example +(concat "abc" "-def") + @result{} "abc-def" +(concat "abc" (list 120 (+ 256 121)) [122]) + @result{} "abcxyz" +;; @r{@code{nil} is an empty sequence.} +(concat "abc" nil "-def") + @result{} "abc-def" +(concat "The " "quick brown " "fox.") + @result{} "The quick brown fox." +(concat) + @result{} "" +@end example + +@noindent +The second example above shows how characters stored in strings are +taken modulo 256. In other words, each character in the string is +stored in one byte. + +The @code{concat} function always constructs a new string that is +not @code{eq} to any existing string. + +When an argument is an integer (not a sequence of integers), it is +converted to a string of digits making up the decimal printed +representation of the integer. @strong{Don't use this feature; we plan +to eliminate it. If you already use this feature, change your programs +now!} The proper way to convert an integer to a decimal number in this +way is with @code{format} (@pxref{Formatting Strings}) or +@code{number-to-string} (@pxref{String Conversion}). + +@example +@group +(concat 137) + @result{} "137" +(concat 54 321) + @result{} "54321" +@end group +@end example + +For information about other concatenation functions, see the description +of @code{mapconcat} in @ref{Mapping Functions}, @code{vconcat} in +@ref{Vectors}, @code{bvconcat} in @ref{Bit Vectors}, and @code{append} +in @ref{Building Lists}. +@end defun + +@node Predicates for Characters +@section The Predicates for Characters + +@defun characterp object +This function returns @code{t} if @var{object} is a character. + +Some functions that work on integers (e.g. the comparison functions +<, <=, =, /=, etc. and the arithmetic functions +, -, *, etc.) +accept characters and implicitly convert them into integers. In +general, functions that work on characters also accept char-ints and +implicitly convert them into characters. WARNING: Neither of these +behaviors is very desirable, and they are maintained for backward +compatibility with old E-Lisp programs that confounded characters and +integers willy-nilly. These behaviors may change in the future; therefore, +do not rely on them. Instead, convert the characters explicitly +using @code{char-int}. +@end defun + +@defun integer-or-char-p object +This function returns @code{t} if @var{object} is an integer or character. +@end defun + +@node Character Codes +@section Character Codes + +@defun char-int ch +This function converts a character into an equivalent integer. +The resulting integer will always be non-negative. The integers in +the range 0 - 255 map to characters as follows: + +@table @asis +@item 0 - 31 +Control set 0 +@item 32 - 127 +@sc{ASCII} +@item 128 - 159 +Control set 1 +@item 160 - 255 +Right half of ISO-8859-1 +@end table + +If support for @sc{MULE} does not exist, these are the only valid +character values. When @sc{MULE} support exists, the values assigned to +other characters may vary depending on the particular version of XEmacs, +the order in which character sets were loaded, etc., and you should not +depend on them. +@end defun + +@defun int-char integer +This function converts an integer into the equivalent character. Not +all integers correspond to valid characters; use @code{char-int-p} to +determine whether this is the case. If the integer cannot be converted, +@code{nil} is returned. +@end defun + +@defun char-int-p object +This function returns @code{t} if @var{object} is an integer that can be +converted into a character. +@end defun + +@defun char-or-char-int-p object +This function returns @code{t} if @var{object} is a character or an +integer that can be converted into one. +@end defun + +@need 2000 +@node Text Comparison +@section Comparison of Characters and Strings +@cindex string equality + +@defun char-equal character1 character2 +This function returns @code{t} if the arguments represent the same +character, @code{nil} otherwise. This function ignores differences +in case if @code{case-fold-search} is non-@code{nil}. + +@example +(char-equal ?x ?x) + @result{} t +(char-to-string (+ 256 ?x)) + @result{} "x" +(char-equal ?x (+ 256 ?x)) + @result{} t +@end example +@end defun + +@defun string= string1 string2 +This function returns @code{t} if the characters of the two strings +match exactly; case is significant. + +@example +(string= "abc" "abc") + @result{} t +(string= "abc" "ABC") + @result{} nil +(string= "ab" "ABC") + @result{} nil +@end example + +@ignore @c `equal' in XEmacs does not compare text properties +The function @code{string=} ignores the text properties of the +two strings. To compare strings in a way that compares their text +properties also, use @code{equal} (@pxref{Equality Predicates}). +@end ignore +@end defun + +@defun string-equal string1 string2 +@code{string-equal} is another name for @code{string=}. +@end defun + +@cindex lexical comparison +@defun string< string1 string2 +@c (findex string< causes problems for permuted index!!) +This function compares two strings a character at a time. First it +scans both the strings at once to find the first pair of corresponding +characters that do not match. If the lesser character of those two is +the character from @var{string1}, then @var{string1} is less, and this +function returns @code{t}. If the lesser character is the one from +@var{string2}, then @var{string1} is greater, and this function returns +@code{nil}. If the two strings match entirely, the value is @code{nil}. + +Pairs of characters are compared by their @sc{ASCII} codes. Keep in +mind that lower case letters have higher numeric values in the +@sc{ASCII} character set than their upper case counterparts; numbers and +many punctuation characters have a lower numeric value than upper case +letters. + +@example +@group +(string< "abc" "abd") + @result{} t +(string< "abd" "abc") + @result{} nil +(string< "123" "abc") + @result{} t +@end group +@end example + +When the strings have different lengths, and they match up to the +length of @var{string1}, then the result is @code{t}. If they match up +to the length of @var{string2}, the result is @code{nil}. A string of +no characters is less than any other string. + +@example +@group +(string< "" "abc") + @result{} t +(string< "ab" "abc") + @result{} t +(string< "abc" "") + @result{} nil +(string< "abc" "ab") + @result{} nil +(string< "" "") + @result{} nil +@end group +@end example +@end defun + +@defun string-lessp string1 string2 +@code{string-lessp} is another name for @code{string<}. +@end defun + + See also @code{compare-buffer-substrings} in @ref{Comparing Text}, for +a way to compare text in buffers. The function @code{string-match}, +which matches a regular expression against a string, can be used +for a kind of string comparison; see @ref{Regexp Search}. + +@node String Conversion +@section Conversion of Characters and Strings +@cindex conversion of strings + + This section describes functions for conversions between characters, +strings and integers. @code{format} and @code{prin1-to-string} +(@pxref{Output Functions}) can also convert Lisp objects into strings. +@code{read-from-string} (@pxref{Input Functions}) can ``convert'' a +string representation of a Lisp object into an object. + + @xref{Documentation}, for functions that produce textual descriptions +of text characters and general input events +(@code{single-key-description} and @code{text-char-description}). These +functions are used primarily for making help messages. + +@defun char-to-string character +@cindex character to string + This function returns a new string with a length of one character. +The value of @var{character}, modulo 256, is used to initialize the +element of the string. + +This function is similar to @code{make-string} with an integer argument +of 1. (@xref{Creating Strings}.) This conversion can also be done with +@code{format} using the @samp{%c} format specification. +(@xref{Formatting Strings}.) + +@example +(char-to-string ?x) + @result{} "x" +(char-to-string (+ 256 ?x)) + @result{} "x" +(make-string 1 ?x) + @result{} "x" +@end example +@end defun + +@defun string-to-char string +@cindex string to character + This function returns the first character in @var{string}. If the +string is empty, the function returns 0. (Under XEmacs 19, the value is +also 0 when the first character of @var{string} is the null character, +@sc{ASCII} code 0.) + +@example +(string-to-char "ABC") + @result{} ?A ;; @r{Under XEmacs 20.} + @result{} 65 ;; @r{Under XEmacs 19.} +(string-to-char "xyz") + @result{} ?x ;; @r{Under XEmacs 20.} + @result{} 120 ;; @r{Under XEmacs 19.} +(string-to-char "") + @result{} 0 +(string-to-char "\000") + @result{} ?\^@ ;; @r{Under XEmacs 20.} + @result{} 0 ;; @r{Under XEmacs 20.} +@end example + +This function may be eliminated in the future if it does not seem useful +enough to retain. +@end defun + +@defun number-to-string number +@cindex integer to string +@cindex integer to decimal +This function returns a string consisting of the printed +representation of @var{number}, which may be an integer or a floating +point number. The value starts with a sign if the argument is +negative. + +@example +(number-to-string 256) + @result{} "256" +(number-to-string -23) + @result{} "-23" +(number-to-string -23.5) + @result{} "-23.5" +@end example + +@cindex int-to-string +@code{int-to-string} is a semi-obsolete alias for this function. + +See also the function @code{format} in @ref{Formatting Strings}. +@end defun + +@defun string-to-number string +@cindex string to number +This function returns the numeric value of the characters in +@var{string}, read in base ten. It skips spaces and tabs at the +beginning of @var{string}, then reads as much of @var{string} as it can +interpret as a number. (On some systems it ignores other whitespace at +the beginning, not just spaces and tabs.) If the first character after +the ignored whitespace is not a digit or a minus sign, this function +returns 0. + +@example +(string-to-number "256") + @result{} 256 +(string-to-number "25 is a perfect square.") + @result{} 25 +(string-to-number "X256") + @result{} 0 +(string-to-number "-4.5") + @result{} -4.5 +@end example + +@findex string-to-int +@code{string-to-int} is an obsolete alias for this function. +@end defun + +@node Modifying Strings +@section Modifying Strings +@cindex strings, modifying + +You can modify a string using the general array-modifying primitives. +@xref{Arrays}. The function @code{aset} modifies a single character; +the function @code{fillarray} sets all characters in the string to +a specified character. + +Each string has a tick counter that starts out at zero (when the string +is created) and is incremented each time a change is made to that +string. + +@defun string-modified-tick string +This function returns the tick counter for @samp{string}. +@end defun + +@node String Properties +@section String Properties +@cindex string properties +@cindex properties of strings + +Similar to symbols, extents, faces, and glyphs, you can attach +additional information to strings in the form of @dfn{string +properties}. These differ from text properties, which are logically +attached to particular characters in the string. + +To attach a property to a string, use @code{put}. To retrieve a property +from a string, use @code{get}. You can also use @code{remprop} to remove +a property from a string and @code{object-props} to retrieve a list of +all the properties in a string. + +@node Formatting Strings +@section Formatting Strings +@cindex formatting strings +@cindex strings, formatting them + + @dfn{Formatting} means constructing a string by substitution of +computed values at various places in a constant string. This string +controls how the other values are printed as well as where they appear; +it is called a @dfn{format string}. + + Formatting is often useful for computing messages to be displayed. In +fact, the functions @code{message} and @code{error} provide the same +formatting feature described here; they differ from @code{format} only +in how they use the result of formatting. + +@defun format string &rest objects + This function returns a new string that is made by copying +@var{string} and then replacing any format specification +in the copy with encodings of the corresponding @var{objects}. The +arguments @var{objects} are the computed values to be formatted. +@end defun + +@cindex @samp{%} in format +@cindex format specification + A format specification is a sequence of characters beginning with a +@samp{%}. Thus, if there is a @samp{%d} in @var{string}, the +@code{format} function replaces it with the printed representation of +one of the values to be formatted (one of the arguments @var{objects}). +For example: + +@example +@group +(format "The value of fill-column is %d." fill-column) + @result{} "The value of fill-column is 72." +@end group +@end example + + If @var{string} contains more than one format specification, the +format specifications correspond with successive values from +@var{objects}. Thus, the first format specification in @var{string} +uses the first such value, the second format specification uses the +second such value, and so on. Any extra format specifications (those +for which there are no corresponding values) cause unpredictable +behavior. Any extra values to be formatted are ignored. + + Certain format specifications require values of particular types. +However, no error is signaled if the value actually supplied fails to +have the expected type. Instead, the output is likely to be +meaningless. + + Here is a table of valid format specifications: + +@table @samp +@item %s +Replace the specification with the printed representation of the object, +made without quoting. Thus, strings are represented by their contents +alone, with no @samp{"} characters, and symbols appear without @samp{\} +characters. This is equivalent to printing the object with @code{princ}. + +If there is no corresponding object, the empty string is used. + +@item %S +Replace the specification with the printed representation of the object, +made with quoting. Thus, strings are enclosed in @samp{"} characters, +and @samp{\} characters appear where necessary before special characters. +This is equivalent to printing the object with @code{prin1}. + +If there is no corresponding object, the empty string is used. + +@item %o +@cindex integer to octal +Replace the specification with the base-eight representation of an +integer. + +@item %d +@itemx %i +Replace the specification with the base-ten representation of an +integer. + +@item %x +@cindex integer to hexadecimal +Replace the specification with the base-sixteen representation of an +integer, using lowercase letters. + +@item %X +@cindex integer to hexadecimal +Replace the specification with the base-sixteen representation of an +integer, using uppercase letters. + +@item %c +Replace the specification with the character which is the value given. + +@item %e +Replace the specification with the exponential notation for a floating +point number (e.g. @samp{7.85200e+03}). + +@item %f +Replace the specification with the decimal-point notation for a floating +point number. + +@item %g +Replace the specification with notation for a floating point number, +using a ``pretty format''. Either exponential notation or decimal-point +notation will be used (usually whichever is shorter), and trailing +zeroes are removed from the fractional part. + +@item %% +A single @samp{%} is placed in the string. This format specification is +unusual in that it does not use a value. For example, @code{(format "%% +%d" 30)} returns @code{"% 30"}. +@end table + + Any other format character results in an @samp{Invalid format +operation} error. + + Here are several examples: + +@example +@group +(format "The name of this buffer is %s." (buffer-name)) + @result{} "The name of this buffer is strings.texi." + +(format "The buffer object prints as %s." (current-buffer)) + @result{} "The buffer object prints as #<buffer strings.texi>." + +(format "The octal value of %d is %o, + and the hex value is %x." 18 18 18) + @result{} "The octal value of 18 is 22, + and the hex value is 12." +@end group +@end example + + There are many additional flags and specifications that can occur +between the @samp{%} and the format character, in the following order: + +@enumerate +@item +An optional repositioning specification, which is a positive +integer followed by a @samp{$}. + +@item +Zero or more of the optional flag characters @samp{-}, @samp{+}, +@samp{ }, @samp{0}, and @samp{#}. + +@item +An optional minimum field width. + +@item +An optional precision, preceded by a @samp{.} character. +@end enumerate + +@cindex repositioning format arguments +@cindex multilingual string formatting + A @dfn{repositioning} specification changes which argument to +@code{format} is used by the current and all following format +specifications. Normally the first specification uses the first +argument, the second specification uses the second argument, etc. Using +a repositioning specification, you can change this. By placing a number +@var{N} followed by a @samp{$} between the @samp{%} and the format +character, you cause the specification to use the @var{N}th argument. +The next specification will use the @var{N}+1'th argument, etc. + +For example: + +@example +@group +(format "Can't find file `%s' in directory `%s'." + "ignatius.c" "loyola/") + @result{} "Can't find file `ignatius.c' in directory `loyola/'." + +(format "In directory `%2$s', the file `%1$s' was not found." + "ignatius.c" "loyola/") + @result{} "In directory `loyola/', the file `ignatius.c' was not found." + +(format + "The numbers %d and %d are %1$x and %x in hex and %1$o and %o in octal." + 37 12) +@result{} "The numbers 37 and 12 are 25 and c in hex and 45 and 14 in octal." +@end group +@end example + +As you can see, this lets you reprocess arguments more than once or +reword a format specification (thereby moving the arguments around) +without having to actually reorder the arguments. This is especially +useful in translating messages from one language to another: Different +languages use different word orders, and this sometimes entails changing +the order of the arguments. By using repositioning specifications, +this can be accomplished without having to embed knowledge of particular +languages into the location in the program's code where the message is +displayed. + +@cindex numeric prefix +@cindex field width +@cindex padding + All the specification characters allow an optional numeric prefix +between the @samp{%} and the character, and following any repositioning +specification or flag. The optional numeric prefix defines the minimum +width for the object. If the printed representation of the object +contains fewer characters than this, then it is padded. The padding is +normally on the left, but will be on the right if the @samp{-} flag +character is given. The padding character is normally a space, but if +the @samp{0} flag character is given, zeros are used for padding. + +@example +(format "%06d is padded on the left with zeros" 123) + @result{} "000123 is padded on the left with zeros" + +(format "%-6d is padded on the right" 123) + @result{} "123 is padded on the right" +@end example + + @code{format} never truncates an object's printed representation, no +matter what width you specify. Thus, you can use a numeric prefix to +specify a minimum spacing between columns with no risk of losing +information. + + In the following three examples, @samp{%7s} specifies a minimum width +of 7. In the first case, the string inserted in place of @samp{%7s} has +only 3 letters, so 4 blank spaces are inserted for padding. In the +second case, the string @code{"specification"} is 13 letters wide but is +not truncated. In the third case, the padding is on the right. + +@smallexample +@group +(format "The word `%7s' actually has %d letters in it." + "foo" (length "foo")) + @result{} "The word ` foo' actually has 3 letters in it." +@end group + +@group +(format "The word `%7s' actually has %d letters in it." + "specification" (length "specification")) + @result{} "The word `specification' actually has 13 letters in it." +@end group + +@group +(format "The word `%-7s' actually has %d letters in it." + "foo" (length "foo")) + @result{} "The word `foo ' actually has 3 letters in it." +@end group +@end smallexample + +@cindex format precision +@cindex precision of formatted numbers + After any minimum field width, a precision may be specified by +preceding it with a @samp{.} character. The precision specifies the +minimum number of digits to appear in @samp{%d}, @samp{%i}, @samp{%o}, +@samp{%x}, and @samp{%X} conversions (the number is padded on the left +with zeroes as necessary); the number of digits printed after the +decimal point for @samp{%f}, @samp{%e}, and @samp{%E} conversions; the +number of significant digits printed in @samp{%g} and @samp{%G} +conversions; and the maximum number of non-padding characters printed in +@samp{%s} and @samp{%S} conversions. The default precision for +floating-point conversions is six. + +The other flag characters have the following meanings: + +@itemize @bullet +@item +The @samp{ } flag means prefix non-negative numbers with a space. + +@item +The @samp{+} flag means prefix non-negative numbers with a plus sign. + +@item +The @samp{#} flag means print numbers in an alternate, more verbose +format: octal numbers begin with zero; hex numbers begin with a +@samp{0x} or @samp{0X}; a decimal point is printed in @samp{%f}, +@samp{%e}, and @samp{%E} conversions even if no numbers are printed +after it; and trailing zeroes are not omitted in @samp{%g} and @samp{%G} +conversions. +@end itemize + +@node Character Case +@section Character Case +@cindex upper case +@cindex lower case +@cindex character case + + The character case functions change the case of single characters or +of the contents of strings. The functions convert only alphabetic +characters (the letters @samp{A} through @samp{Z} and @samp{a} through +@samp{z}); other characters are not altered. The functions do not +modify the strings that are passed to them as arguments. + + The examples below use the characters @samp{X} and @samp{x} which have +@sc{ASCII} codes 88 and 120 respectively. + +@defun downcase string-or-char +This function converts a character or a string to lower case. + +When the argument to @code{downcase} is a string, the function creates +and returns a new string in which each letter in the argument that is +upper case is converted to lower case. When the argument to +@code{downcase} is a character, @code{downcase} returns the +corresponding lower case character. (This value is actually an integer +under XEmacs 19.) If the original character is lower case, or is not a +letter, then the value equals the original character. + +@example +(downcase "The cat in the hat") + @result{} "the cat in the hat" + +(downcase ?X) + @result{} ?x ;; @r{Under XEmacs 20.} + @result{} 120 ;; @r{Under XEmacs 19.} + +@end example +@end defun + +@defun upcase string-or-char +This function converts a character or a string to upper case. + +When the argument to @code{upcase} is a string, the function creates +and returns a new string in which each letter in the argument that is +lower case is converted to upper case. + +When the argument to @code{upcase} is a character, @code{upcase} returns +the corresponding upper case character. (This value is actually an +integer under XEmacs 19.) If the original character is upper case, or +is not a letter, then the value equals the original character. + +@example +(upcase "The cat in the hat") + @result{} "THE CAT IN THE HAT" + +(upcase ?x) + @result{} ?X ;; @r{Under XEmacs 20.} + @result{} 88 ;; @r{Under XEmacs 19.} +@end example +@end defun + +@defun capitalize string-or-char +@cindex capitalization +This function capitalizes strings or characters. If +@var{string-or-char} is a string, the function creates and returns a new +string, whose contents are a copy of @var{string-or-char} in which each +word has been capitalized. This means that the first character of each +word is converted to upper case, and the rest are converted to lower +case. + +The definition of a word is any sequence of consecutive characters that +are assigned to the word constituent syntax class in the current syntax +table (@xref{Syntax Class Table}). + +When the argument to @code{capitalize} is a character, @code{capitalize} +has the same result as @code{upcase}. + +@example +(capitalize "The cat in the hat") + @result{} "The Cat In The Hat" + +(capitalize "THE 77TH-HATTED CAT") + @result{} "The 77th-Hatted Cat" + +@group +(capitalize ?x) + @result{} ?X ;; @r{Under XEmacs 20.} + @result{} 88 ;; @r{Under XEmacs 19.} +@end group +@end example +@end defun + +@node Case Tables +@section The Case Table + + You can customize case conversion by installing a special @dfn{case +table}. A case table specifies the mapping between upper case and lower +case letters. It affects both the string and character case conversion +functions (see the previous section) and those that apply to text in the +buffer (@pxref{Case Changes}). You need a case table if you are using a +language which has letters other than the standard @sc{ASCII} letters. + + A case table is a list of this form: + +@example +(@var{downcase} @var{upcase} @var{canonicalize} @var{equivalences}) +@end example + +@noindent +where each element is either @code{nil} or a string of length 256. The +element @var{downcase} says how to map each character to its lower-case +equivalent. The element @var{upcase} maps each character to its +upper-case equivalent. If lower and upper case characters are in +one-to-one correspondence, use @code{nil} for @var{upcase}; then XEmacs +deduces the upcase table from @var{downcase}. + + For some languages, upper and lower case letters are not in one-to-one +correspondence. There may be two different lower case letters with the +same upper case equivalent. In these cases, you need to specify the +maps for both directions. + + The element @var{canonicalize} maps each character to a canonical +equivalent; any two characters that are related by case-conversion have +the same canonical equivalent character. + + The element @var{equivalences} is a map that cyclicly permutes each +equivalence class (of characters with the same canonical equivalent). +(For ordinary @sc{ASCII}, this would map @samp{a} into @samp{A} and +@samp{A} into @samp{a}, and likewise for each set of equivalent +characters.) + + When you construct a case table, you can provide @code{nil} for +@var{canonicalize}; then Emacs fills in this string from @var{upcase} +and @var{downcase}. You can also provide @code{nil} for +@var{equivalences}; then Emacs fills in this string from +@var{canonicalize}. In a case table that is actually in use, those +components are non-@code{nil}. Do not try to specify @var{equivalences} +without also specifying @var{canonicalize}. + + Each buffer has a case table. XEmacs also has a @dfn{standard case +table} which is copied into each buffer when you create the buffer. +Changing the standard case table doesn't affect any existing buffers. + + Here are the functions for working with case tables: + +@defun case-table-p object +This predicate returns non-@code{nil} if @var{object} is a valid case +table. +@end defun + +@defun set-standard-case-table table +This function makes @var{table} the standard case table, so that it will +apply to any buffers created subsequently. +@end defun + +@defun standard-case-table +This returns the standard case table. +@end defun + +@defun current-case-table +This function returns the current buffer's case table. +@end defun + +@defun set-case-table table +This sets the current buffer's case table to @var{table}. +@end defun + + The following three functions are convenient subroutines for packages +that define non-@sc{ASCII} character sets. They modify a string +@var{downcase-table} provided as an argument; this should be a string to +be used as the @var{downcase} part of a case table. They also modify +the standard syntax table. @xref{Syntax Tables}. + +@defun set-case-syntax-pair uc lc downcase-table +This function specifies a pair of corresponding letters, one upper case +and one lower case. +@end defun + +@defun set-case-syntax-delims l r downcase-table +This function makes characters @var{l} and @var{r} a matching pair of +case-invariant delimiters. +@end defun + +@defun set-case-syntax char syntax downcase-table +This function makes @var{char} case-invariant, with syntax +@var{syntax}. +@end defun + +@deffn Command describe-buffer-case-table +This command displays a description of the contents of the current +buffer's case table. +@end deffn + +@cindex ISO Latin 1 +@pindex iso-syntax +You can load the library @file{iso-syntax} to set up the standard syntax +table and define a case table for the 8-bit ISO Latin 1 character set. + +@node Char Tables +@section The Char Table + +A char table is a table that maps characters (or ranges of characters) +to values. Char tables are specialized for characters, only allowing +particular sorts of ranges to be assigned values. Although this +loses in generality, it makes for extremely fast (constant-time) +lookups, and thus is feasible for applications that do an extremely +large number of lookups (e.g. scanning a buffer for a character in +a particular syntax, where a lookup in the syntax table must occur +once per character). + +Note that char tables as a primitive type, and all of the functions in +this section, exist only in XEmacs 20. In XEmacs 19, char tables are +generally implemented using a vector of 256 elements. + +When @sc{MULE} support exists, the types of ranges that can be assigned +values are + +@itemize @bullet +@item +all characters +@item +an entire charset +@item +a single row in a two-octet charset +@item +a single character +@end itemize + +When @sc{MULE} support is not present, the types of ranges that can be +assigned values are + +@itemize @bullet +@item +all characters +@item +a single character +@end itemize + +@defun char-table-p object +This function returns non-@code{nil} if @var{object} is a char table. +@end defun + +@menu +* Char Table Types:: Char tables have different uses. +* Working With Char Tables:: Creating and working with char tables. +@end menu + +@node Char Table Types +@subsection Char Table Types + +Each char table type is used for a different purpose and allows different +sorts of values. The different char table types are + +@table @code +@item category +Used for category tables, which specify the regexp categories +that a character is in. The valid values are @code{nil} or a +bit vector of 95 elements. Higher-level Lisp functions are +provided for working with category tables. Currently categories +and category tables only exist when @sc{MULE} support is present. +@item char +A generalized char table, for mapping from one character to +another. Used for case tables, syntax matching tables, +@code{keyboard-translate-table}, etc. The valid values are characters. +@item generic +An even more generalized char table, for mapping from a +character to anything. +@item display +Used for display tables, which specify how a particular character +is to appear when displayed. #### Not yet implemented. +@item syntax +Used for syntax tables, which specify the syntax of a particular +character. Higher-level Lisp functions are provided for +working with syntax tables. The valid values are integers. +@end table + +@defun char-table-type table +This function returns the type of char table @var{table}. +@end defun + +@defun char-table-type-list +This function returns a list of the recognized char table types. +@end defun + +@defun valid-char-table-type-p type +This function returns @code{t} if @var{type} if a recognized char table type. +@end defun + +@node Working With Char Tables +@subsection Working With Char Tables + +@defun make-char-table type +This function makes a new, empty char table of type @var{type}. +@var{type} should be a symbol, one of @code{char}, @code{category}, +@code{display}, @code{generic}, or @code{syntax}. +@end defun + +@defun put-char-table range val table +This function sets the value for chars in @var{range} to be @var{val} in +@var{table}. + +@var{range} specifies one or more characters to be affected and should be +one of the following: + +@itemize @bullet +@item +@code{t} (all characters are affected) +@item +A charset (only allowed when @sc{MULE} support is present) +@item +A vector of two elements: a two-octet charset and a row number +(only allowed when @sc{MULE} support is present) +@item +A single character +@end itemize + +@var{val} must be a value appropriate for the type of @var{table}. +@end defun + +@defun get-char-table ch table +This function finds the value for char @var{ch} in @var{table}. +@end defun + +@defun get-range-char-table range table &optional multi +This function finds the value for a range in @var{table}. If there is +more than one value, @var{multi} is returned (defaults to @code{nil}). +@end defun + +@defun reset-char-table table +This function resets a char table to its default state. +@end defun + +@defun map-char-table function table &optional range +This function maps @var{function} over entries in @var{table}, calling +it with two args, each key and value in the table. + +@var{range} specifies a subrange to map over and is in the same format +as the @var{range} argument to @code{put-range-table}. If omitted or +@code{t}, it defaults to the entire table. +@end defun + +@defun valid-char-table-value-p value char-table-type +This function returns non-@code{nil} if @var{value} is a valid value for +@var{char-table-type}. +@end defun + +@defun check-valid-char-table-value value char-table-type +This function signals an error if @var{value} is not a valid value for +@var{char-table-type}. +@end defun