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1115 lines
40 KiB
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1115 lines
40 KiB
Plaintext
@c -*-texinfo-*-
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@c This is part of the GNU Emacs Lisp Reference Manual.
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@c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999, 2003
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@c Free Software Foundation, Inc.
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@c See the file elisp.texi for copying conditions.
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@setfilename ../info/strings
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@node Strings and Characters, Lists, Numbers, Top
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@comment node-name, next, previous, up
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@chapter Strings and Characters
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@cindex strings
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@cindex character arrays
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@cindex characters
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@cindex bytes
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A string in Emacs Lisp is an array that contains an ordered sequence
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of characters. Strings are used as names of symbols, buffers, and
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files; to send messages to users; to hold text being copied between
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buffers; and for many other purposes. Because strings are so important,
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Emacs Lisp has many functions expressly for manipulating them. Emacs
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Lisp programs use strings more often than individual characters.
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@xref{Strings of Events}, for special considerations for strings of
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keyboard character events.
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@menu
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* Basics: String Basics. Basic properties of strings and characters.
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* Predicates for Strings:: Testing whether an object is a string or char.
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* Creating Strings:: Functions to allocate new strings.
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* Modifying Strings:: Altering the contents of an existing string.
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* Text Comparison:: Comparing characters or strings.
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* String Conversion:: Converting to and from characters and strings.
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* Formatting Strings:: @code{format}: Emacs's analogue of @code{printf}.
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* Case Conversion:: Case conversion functions.
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* Case Tables:: Customizing case conversion.
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@end menu
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@node String Basics
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@section String and Character Basics
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Characters are represented in Emacs Lisp as integers;
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whether an integer is a character or not is determined only by how it is
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used. Thus, strings really contain integers.
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The length of a string (like any array) is fixed, and cannot be
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altered once the string exists. Strings in Lisp are @emph{not}
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terminated by a distinguished character code. (By contrast, strings in
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C are terminated by a character with @acronym{ASCII} code 0.)
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Since strings are arrays, and therefore sequences as well, you can
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operate on them with the general array and sequence functions.
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(@xref{Sequences Arrays Vectors}.) For example, you can access or
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change individual characters in a string using the functions @code{aref}
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and @code{aset} (@pxref{Array Functions}).
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There are two text representations for non-@acronym{ASCII} characters in
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Emacs strings (and in buffers): unibyte and multibyte (@pxref{Text
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Representations}). An @acronym{ASCII} character always occupies one byte in a
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string; in fact, when a string is all @acronym{ASCII}, there is no real
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difference between the unibyte and multibyte representations.
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For most Lisp programming, you don't need to be concerned with these two
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representations.
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Sometimes key sequences are represented as strings. When a string is
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a key sequence, string elements in the range 128 to 255 represent meta
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characters (which are large integers) rather than character
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codes in the range 128 to 255.
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Strings cannot hold characters that have the hyper, super or alt
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modifiers; they can hold @acronym{ASCII} control characters, but no other
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control characters. They do not distinguish case in @acronym{ASCII} control
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characters. If you want to store such characters in a sequence, such as
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a key sequence, you must use a vector instead of a string.
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@xref{Character Type}, for more information about the representation of meta
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and other modifiers for keyboard input characters.
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Strings are useful for holding regular expressions. You can also
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match regular expressions against strings with @code{string-match}
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(@pxref{Regexp Search}). The functions @code{match-string}
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(@pxref{Simple Match Data}) and @code{replace-match} (@pxref{Replacing
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Match}) are useful for decomposing and modifying strings after
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matching regular expressions against them.
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Like a buffer, a string can contain text properties for the characters
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in it, as well as the characters themselves. @xref{Text Properties}.
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All the Lisp primitives that copy text from strings to buffers or other
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strings also copy the properties of the characters being copied.
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@xref{Text}, for information about functions that display strings or
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copy them into buffers. @xref{Character Type}, and @ref{String Type},
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for information about the syntax of characters and strings.
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@xref{Non-ASCII Characters}, for functions to convert between text
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representations and to encode and decode character codes.
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@node Predicates for Strings
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@section The Predicates for Strings
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For more information about general sequence and array predicates,
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see @ref{Sequences Arrays Vectors}, and @ref{Arrays}.
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@defun stringp object
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This function returns @code{t} if @var{object} is a string, @code{nil}
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otherwise.
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@end defun
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@defun char-or-string-p object
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This function returns @code{t} if @var{object} is a string or a
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character (i.e., an integer), @code{nil} otherwise.
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@end defun
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@node Creating Strings
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@section Creating Strings
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The following functions create strings, either from scratch, or by
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putting strings together, or by taking them apart.
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@defun make-string count character
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This function returns a string made up of @var{count} repetitions of
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@var{character}. If @var{count} is negative, an error is signaled.
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@example
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(make-string 5 ?x)
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@result{} "xxxxx"
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(make-string 0 ?x)
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@result{} ""
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@end example
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Other functions to compare with this one include @code{char-to-string}
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(@pxref{String Conversion}), @code{make-vector} (@pxref{Vectors}), and
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@code{make-list} (@pxref{Building Lists}).
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@end defun
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@defun string &rest characters
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This returns a string containing the characters @var{characters}.
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@example
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(string ?a ?b ?c)
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@result{} "abc"
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@end example
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@end defun
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@defun substring string start &optional end
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This function returns a new string which consists of those characters
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from @var{string} in the range from (and including) the character at the
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index @var{start} up to (but excluding) the character at the index
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@var{end}. The first character is at index zero.
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@example
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@group
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(substring "abcdefg" 0 3)
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@result{} "abc"
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@end group
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@end example
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@noindent
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Here the index for @samp{a} is 0, the index for @samp{b} is 1, and the
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index for @samp{c} is 2. Thus, three letters, @samp{abc}, are copied
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from the string @code{"abcdefg"}. The index 3 marks the character
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position up to which the substring is copied. The character whose index
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is 3 is actually the fourth character in the string.
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A negative number counts from the end of the string, so that @minus{}1
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signifies the index of the last character of the string. For example:
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@example
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@group
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(substring "abcdefg" -3 -1)
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@result{} "ef"
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@end group
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@end example
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@noindent
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In this example, the index for @samp{e} is @minus{}3, the index for
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@samp{f} is @minus{}2, and the index for @samp{g} is @minus{}1.
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Therefore, @samp{e} and @samp{f} are included, and @samp{g} is excluded.
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When @code{nil} is used for @var{end}, it stands for the length of the
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string. Thus,
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@example
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@group
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(substring "abcdefg" -3 nil)
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@result{} "efg"
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@end group
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@end example
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Omitting the argument @var{end} is equivalent to specifying @code{nil}.
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It follows that @code{(substring @var{string} 0)} returns a copy of all
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of @var{string}.
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@example
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@group
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(substring "abcdefg" 0)
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@result{} "abcdefg"
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@end group
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@end example
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@noindent
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But we recommend @code{copy-sequence} for this purpose (@pxref{Sequence
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Functions}).
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If the characters copied from @var{string} have text properties, the
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properties are copied into the new string also. @xref{Text Properties}.
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@code{substring} also accepts a vector for the first argument.
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For example:
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@example
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(substring [a b (c) "d"] 1 3)
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@result{} [b (c)]
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@end example
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A @code{wrong-type-argument} error is signaled if @var{start} is not
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an integer or if @var{end} is neither an integer nor @code{nil}. An
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@code{args-out-of-range} error is signaled if @var{start} indicates a
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character following @var{end}, or if either integer is out of range
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for @var{string}.
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Contrast this function with @code{buffer-substring} (@pxref{Buffer
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Contents}), which returns a string containing a portion of the text in
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the current buffer. The beginning of a string is at index 0, but the
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beginning of a buffer is at index 1.
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@end defun
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@defun substring-no-properties string &optional start end
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This works like @code{substring} but discards all text properties from
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the value. Also, @var{start} may be omitted or @code{nil}, which is
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equivalent to 0. Thus, @w{@code{(substring-no-properties
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@var{string})}} returns a copy of @var{string}, with all text
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properties removed.
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@end defun
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@defun concat &rest sequences
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@cindex copying strings
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@cindex concatenating strings
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This function returns a new string consisting of the characters in the
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arguments passed to it (along with their text properties, if any). The
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arguments may be strings, lists of numbers, or vectors of numbers; they
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are not themselves changed. If @code{concat} receives no arguments, it
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returns an empty string.
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@example
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(concat "abc" "-def")
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@result{} "abc-def"
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(concat "abc" (list 120 121) [122])
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@result{} "abcxyz"
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;; @r{@code{nil} is an empty sequence.}
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(concat "abc" nil "-def")
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@result{} "abc-def"
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(concat "The " "quick brown " "fox.")
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@result{} "The quick brown fox."
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(concat)
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@result{} ""
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@end example
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@noindent
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The @code{concat} function always constructs a new string that is
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not @code{eq} to any existing string.
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In Emacs versions before 21, when an argument was an integer (not a
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sequence of integers), it was converted to a string of digits making up
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the decimal printed representation of the integer. This obsolete usage
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no longer works. The proper way to convert an integer to its decimal
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printed form is with @code{format} (@pxref{Formatting Strings}) or
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@code{number-to-string} (@pxref{String Conversion}).
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For information about other concatenation functions, see the
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description of @code{mapconcat} in @ref{Mapping Functions},
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@code{vconcat} in @ref{Vector Functions}, and @code{append} in @ref{Building
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Lists}.
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@end defun
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@defun split-string string &optional separators omit-nulls
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This function splits @var{string} into substrings at matches for the
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regular expression @var{separators}. Each match for @var{separators}
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defines a splitting point; the substrings between the splitting points
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are made into a list, which is the value returned by
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@code{split-string}.
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If @var{omit-nulls} is @code{nil}, the result contains null strings
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whenever there are two consecutive matches for @var{separators}, or a
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match is adjacent to the beginning or end of @var{string}. If
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@var{omit-nulls} is @code{t}, these null strings are omitted from the
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result list.
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If @var{separators} is @code{nil} (or omitted),
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the default is the value of @code{split-string-default-separators}.
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As a special case, when @var{separators} is @code{nil} (or omitted),
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null strings are always omitted from the result. Thus:
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@example
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(split-string " two words ")
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@result{} ("two" "words")
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@end example
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The result is not @samp{("" "two" "words" "")}, which would rarely be
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useful. If you need such a result, use an explicit value for
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@var{separators}:
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@example
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(split-string " two words "
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split-string-default-separators)
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@result{} ("" "two" "words" "")
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@end example
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More examples:
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@example
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(split-string "Soup is good food" "o")
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@result{} ("S" "up is g" "" "d f" "" "d")
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(split-string "Soup is good food" "o" t)
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@result{} ("S" "up is g" "d f" "d")
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(split-string "Soup is good food" "o+")
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@result{} ("S" "up is g" "d f" "d")
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@end example
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Empty matches do count, except that @code{split-string} will not look
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for a final empty match when it already reached the end of the string
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using a non-empty match or when @var{string} is empty:
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@example
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(split-string "aooob" "o*")
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@result{} ("" "a" "" "b" "")
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(split-string "ooaboo" "o*")
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@result{} ("" "" "a" "b" "")
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(split-string "" "")
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@result{} ("")
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@end example
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However, when @var{separators} can match the empty string,
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@var{omit-nulls} is usually @code{t}, so that the subtleties in the
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three previous examples are rarely relevant:
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@example
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(split-string "Soup is good food" "o*" t)
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@result{} ("S" "u" "p" " " "i" "s" " " "g" "d" " " "f" "d")
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(split-string "Nice doggy!" "" t)
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@result{} ("N" "i" "c" "e" " " "d" "o" "g" "g" "y" "!")
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(split-string "" "" t)
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@result{} nil
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@end example
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Somewhat odd, but predictable, behavior can occur for certain
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``non-greedy'' values of @var{separators} that can prefer empty
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matches over non-empty matches. Again, such values rarely occur in
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practice:
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@example
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(split-string "ooo" "o*" t)
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@result{} nil
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(split-string "ooo" "\\|o+" t)
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@result{} ("o" "o" "o")
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@end example
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@end defun
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@defvar split-string-default-separators
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The default value of @var{separators} for @code{split-string}. Its
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usual value is @w{@samp{"[ \f\t\n\r\v]+"}}.
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@end defvar
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@node Modifying Strings
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@section Modifying Strings
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The most basic way to alter the contents of an existing string is with
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@code{aset} (@pxref{Array Functions}). @code{(aset @var{string}
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@var{idx} @var{char})} stores @var{char} into @var{string} at index
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@var{idx}. Each character occupies one or more bytes, and if @var{char}
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needs a different number of bytes from the character already present at
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that index, @code{aset} signals an error.
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A more powerful function is @code{store-substring}:
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@defun store-substring string idx obj
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This function alters part of the contents of the string @var{string}, by
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storing @var{obj} starting at index @var{idx}. The argument @var{obj}
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may be either a character or a (smaller) string.
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Since it is impossible to change the length of an existing string, it is
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an error if @var{obj} doesn't fit within @var{string}'s actual length,
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or if any new character requires a different number of bytes from the
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character currently present at that point in @var{string}.
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@end defun
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To clear out a string that contained a password, use
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@code{clear-string}:
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@defun clear-string string
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This clears the contents of @var{string} to zeros.
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It may also change @var{string}'s length and convert it to
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a unibyte string.
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@end defun
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@need 2000
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@node Text Comparison
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@section Comparison of Characters and Strings
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@cindex string equality
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@defun char-equal character1 character2
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This function returns @code{t} if the arguments represent the same
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character, @code{nil} otherwise. This function ignores differences
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in case if @code{case-fold-search} is non-@code{nil}.
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@example
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(char-equal ?x ?x)
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@result{} t
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(let ((case-fold-search nil))
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(char-equal ?x ?X))
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@result{} nil
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@end example
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@end defun
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@defun string= string1 string2
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This function returns @code{t} if the characters of the two strings
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match exactly. Symbols are also allowed as arguments, in which case
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their print names are used.
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Case is always significant, regardless of @code{case-fold-search}.
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@example
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(string= "abc" "abc")
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@result{} t
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(string= "abc" "ABC")
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@result{} nil
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(string= "ab" "ABC")
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@result{} nil
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@end example
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The function @code{string=} ignores the text properties of the two
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strings. When @code{equal} (@pxref{Equality Predicates}) compares two
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strings, it uses @code{string=}.
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For technical reasons, a unibyte and a multibyte string are
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@code{equal} if and only if they contain the same sequence of
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character codes and all these codes are either in the range 0 through
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127 (@acronym{ASCII}) or 160 through 255 (@code{eight-bit-graphic}).
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However, when a unibyte string gets converted to a multibyte string,
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all characters with codes in the range 160 through 255 get converted
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to characters with higher codes, whereas @acronym{ASCII} characters
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remain unchanged. Thus, a unibyte string and its conversion to
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multibyte are only @code{equal} if the string is all @acronym{ASCII}.
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Character codes 160 through 255 are not entirely proper in multibyte
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text, even though they can occur. As a consequence, the situation
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where a unibyte and a multibyte string are @code{equal} without both
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being all @acronym{ASCII} is a technical oddity that very few Emacs
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Lisp programmers ever get confronted with. @xref{Text
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Representations}.
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@end defun
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@defun string-equal string1 string2
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@code{string-equal} is another name for @code{string=}.
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@end defun
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@cindex lexical comparison
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@defun string< string1 string2
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@c (findex string< causes problems for permuted index!!)
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This function compares two strings a character at a time. It
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scans both the strings at the same time to find the first pair of corresponding
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characters that do not match. If the lesser character of these two is
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the character from @var{string1}, then @var{string1} is less, and this
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function returns @code{t}. If the lesser character is the one from
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@var{string2}, then @var{string1} is greater, and this function returns
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@code{nil}. If the two strings match entirely, the value is @code{nil}.
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Pairs of characters are compared according to their character codes.
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Keep in mind that lower case letters have higher numeric values in the
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@acronym{ASCII} character set than their upper case counterparts; digits and
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many punctuation characters have a lower numeric value than upper case
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letters. An @acronym{ASCII} character is less than any non-@acronym{ASCII}
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character; a unibyte non-@acronym{ASCII} character is always less than any
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multibyte non-@acronym{ASCII} character (@pxref{Text Representations}).
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@example
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@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
|
|
|
|
Symbols are also allowed as arguments, in which case their print names
|
|
are used.
|
|
@end defun
|
|
|
|
@defun string-lessp string1 string2
|
|
@code{string-lessp} is another name for @code{string<}.
|
|
@end defun
|
|
|
|
@defun compare-strings string1 start1 end1 string2 start2 end2 &optional ignore-case
|
|
This function compares the specified part of @var{string1} with the
|
|
specified part of @var{string2}. The specified part of @var{string1}
|
|
runs from index @var{start1} up to index @var{end1} (@code{nil} means
|
|
the end of the string). The specified part of @var{string2} runs from
|
|
index @var{start2} up to index @var{end2} (@code{nil} means the end of
|
|
the string).
|
|
|
|
The strings are both converted to multibyte for the comparison
|
|
(@pxref{Text Representations}) so that a unibyte string and its
|
|
conversion to multibyte are always regarded as equal. If
|
|
@var{ignore-case} is non-@code{nil}, then case is ignored, so that
|
|
upper case letters can be equal to lower case letters.
|
|
|
|
If the specified portions of the two strings match, the value is
|
|
@code{t}. Otherwise, the value is an integer which indicates how many
|
|
leading characters agree, and which string is less. Its absolute value
|
|
is one plus the number of characters that agree at the beginning of the
|
|
two strings. The sign is negative if @var{string1} (or its specified
|
|
portion) is less.
|
|
@end defun
|
|
|
|
@defun assoc-string key alist &optional case-fold
|
|
This function works like @code{assoc}, except that @var{key} must be a
|
|
string, and comparison is done using @code{compare-strings}. If
|
|
@var{case-fold} is non-@code{nil}, it ignores case differences.
|
|
Unlike @code{assoc}, this function can also match elements of the alist
|
|
that are strings rather than conses. In particular, @var{alist} can
|
|
be a list of strings rather than an actual alist.
|
|
@xref{Association Lists}.
|
|
@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
|
|
@comment node-name, next, previous, up
|
|
@section Conversion of Characters and Strings
|
|
@cindex conversion of strings
|
|
|
|
This section describes functions for conversions between characters,
|
|
strings and integers. @code{format} (@pxref{Formatting Strings})
|
|
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. The functions
|
|
@code{string-make-multibyte} and @code{string-make-unibyte} convert the
|
|
text representation of a string (@pxref{Converting Representations}).
|
|
|
|
@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 containing one character,
|
|
@var{character}. This function is semi-obsolete because the function
|
|
@code{string} is more general. @xref{Creating Strings}.
|
|
@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. The value is also 0 when the
|
|
first character of @var{string} is the null character, @acronym{ASCII} code
|
|
0.
|
|
|
|
@example
|
|
(string-to-char "ABC")
|
|
@result{} 65
|
|
(string-to-char "xyz")
|
|
@result{} 120
|
|
(string-to-char "")
|
|
@result{} 0
|
|
@group
|
|
(string-to-char "\000")
|
|
@result{} 0
|
|
@end group
|
|
@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 base-ten
|
|
representation of @var{number}, which may be an integer or a floating
|
|
point number. The returned value starts with a minus sign if the argument is
|
|
negative.
|
|
|
|
@example
|
|
(number-to-string 256)
|
|
@result{} "256"
|
|
@group
|
|
(number-to-string -23)
|
|
@result{} "-23"
|
|
@end group
|
|
(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 &optional base
|
|
@cindex string to number
|
|
This function returns the numeric value of the characters in
|
|
@var{string}. If @var{base} is non-@code{nil}, it must be an integer
|
|
between 2 and 16 (inclusive), and integers are converted in that base.
|
|
If @var{base} is @code{nil}, then base ten is used. Floating point
|
|
conversion only works in base ten; we have not implemented other
|
|
radices for floating point numbers, because that would be much more
|
|
work and does not seem useful. If @var{string} looks like an integer
|
|
but its value is too large to fit into a Lisp integer,
|
|
@code{string-to-number} returns a floating point result.
|
|
|
|
The parsing skips spaces and tabs at the beginning of @var{string},
|
|
then reads as much of @var{string} as it can interpret as a number in
|
|
the given base. (On some systems it ignores other whitespace at the
|
|
beginning, not just spaces and tabs.) If the first character after
|
|
the ignored whitespace is neither a digit in the given base, nor a
|
|
plus or minus sign, nor the leading dot of a floating point number,
|
|
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
|
|
(string-to-number "1e5")
|
|
@result{} 100000.0
|
|
@end example
|
|
|
|
@findex string-to-int
|
|
@code{string-to-int} is an obsolete alias for this function.
|
|
@end defun
|
|
|
|
Here are some other functions that can convert to or from a string:
|
|
|
|
@table @code
|
|
@item concat
|
|
@code{concat} can convert a vector or a list into a string.
|
|
@xref{Creating Strings}.
|
|
|
|
@item vconcat
|
|
@code{vconcat} can convert a string into a vector. @xref{Vector
|
|
Functions}.
|
|
|
|
@item append
|
|
@code{append} can convert a string into a list. @xref{Building Lists}.
|
|
@end table
|
|
|
|
@node Formatting Strings
|
|
@comment node-name, next, previous, up
|
|
@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 constant 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.
|
|
|
|
The characters in @var{string}, other than the format specifications,
|
|
are copied directly into the output; if they have text properties,
|
|
these are copied into the output also.
|
|
@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 to 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 an error. Any
|
|
extra values to be formatted are ignored.
|
|
|
|
Certain format specifications require values of particular types. If
|
|
you supply a value that doesn't fit the requirements, an error is
|
|
signaled.
|
|
|
|
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 (that is, using @code{princ}, not
|
|
@code{prin1}---@pxref{Output Functions}). Thus, strings are represented
|
|
by their contents alone, with no @samp{"} characters, and symbols appear
|
|
without @samp{\} characters.
|
|
|
|
If the object is a string, its text properties are
|
|
copied into the output. The text properties of the @samp{%s} itself
|
|
are also copied, but those of the object take priority.
|
|
|
|
@item %S
|
|
Replace the specification with the printed representation of the object,
|
|
made with quoting (that is, using @code{prin1}---@pxref{Output
|
|
Functions}). Thus, strings are enclosed in @samp{"} characters, and
|
|
@samp{\} characters appear where necessary before special characters.
|
|
|
|
@item %o
|
|
@cindex integer to octal
|
|
Replace the specification with the base-eight representation of an
|
|
integer.
|
|
|
|
@item %d
|
|
Replace the specification with the base-ten representation of an
|
|
integer.
|
|
|
|
@item %x
|
|
@itemx %X
|
|
@cindex integer to hexadecimal
|
|
Replace the specification with the base-sixteen representation of an
|
|
integer. @samp{%x} uses lower case and @samp{%X} uses upper case.
|
|
|
|
@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.
|
|
|
|
@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 either exponential notation or decimal-point notation, whichever
|
|
is shorter.
|
|
|
|
@item %%
|
|
Replace the specification with a single @samp{%}. 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 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
|
|
|
|
@cindex field width
|
|
@cindex padding
|
|
All the specification characters allow an optional ``width'', which
|
|
is a digit-string between the @samp{%} and the character. If the
|
|
printed representation of the object contains fewer characters than
|
|
this width, then it is padded. The padding is on the left if the
|
|
width is positive (or starts with zero) and on the right if the
|
|
width is negative. The padding character is normally a space, but if
|
|
the width starts with a zero, zeros are used for padding. Some of
|
|
these conventions are ignored for specification characters for which
|
|
they do not make sense. That is, @samp{%s}, @samp{%S} and @samp{%c}
|
|
accept a width starting with 0, but still pad with @emph{spaces} on
|
|
the left. Also, @samp{%%} accepts a width, but ignores it. Here are
|
|
some examples of 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
|
|
|
|
If the width is too small, @code{format} does not truncate the
|
|
object's printed representation. Thus, you can use a width 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 precision in format specifications
|
|
All the specification characters allow an optional ``precision''
|
|
before the character (after the width, if present). The precision is
|
|
a decimal-point @samp{.} followed by a digit-string. For the
|
|
floating-point specifications (@samp{%e}, @samp{%f}, @samp{%g}), the
|
|
precision specifies how many decimal places to show; if zero, the
|
|
decimal-point itself is also omitted. For @samp{%s} and @samp{%S},
|
|
the precision truncates the string to the given width, so
|
|
@samp{%.3s} shows only the first three characters of the
|
|
representation for @var{object}. Precision is ignored for other
|
|
specification characters.
|
|
|
|
@cindex flags in format specifications
|
|
Immediately after the @samp{%} and before the optional width and
|
|
precision, you can put certain ``flag'' characters.
|
|
|
|
A space character inserts a space for positive numbers (otherwise
|
|
nothing is inserted for positive numbers). This flag is ignored
|
|
except for @samp{%d}, @samp{%e}, @samp{%f}, @samp{%g}.
|
|
|
|
The flag @samp{#} indicates ``alternate form''. For @samp{%o} it
|
|
ensures that the result begins with a 0. For @samp{%x} and @samp{%X}
|
|
the result is prefixed with @samp{0x} or @samp{0X}. For @samp{%e},
|
|
@samp{%f}, and @samp{%g} a decimal point is always shown even if the
|
|
precision is zero.
|
|
|
|
@node Case Conversion
|
|
@comment node-name, next, previous, up
|
|
@section Case Conversion in Lisp
|
|
@cindex upper case
|
|
@cindex lower case
|
|
@cindex character case
|
|
@cindex case conversion in Lisp
|
|
|
|
The character case functions change the case of single characters or
|
|
of the contents of strings. The functions normally convert only
|
|
alphabetic characters (the letters @samp{A} through @samp{Z} and
|
|
@samp{a} through @samp{z}, as well as non-@acronym{ASCII} letters); other
|
|
characters are not altered. You can specify a different case
|
|
conversion mapping by specifying a case table (@pxref{Case Tables}).
|
|
|
|
These 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
|
|
@acronym{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 an integer. 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{} 120
|
|
@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 an integer.
|
|
If the original character is upper case, or is not a letter, then the
|
|
value returned equals the original character.
|
|
|
|
@example
|
|
(upcase "The cat in the hat")
|
|
@result{} "THE CAT IN THE HAT"
|
|
|
|
(upcase ?x)
|
|
@result{} 88
|
|
@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 (@pxref{Syntax Class Table}).
|
|
|
|
When the argument to @code{capitalize} is a character, @code{capitalize}
|
|
has the same result as @code{upcase}.
|
|
|
|
@example
|
|
@group
|
|
(capitalize "The cat in the hat")
|
|
@result{} "The Cat In The Hat"
|
|
@end group
|
|
|
|
@group
|
|
(capitalize "THE 77TH-HATTED CAT")
|
|
@result{} "The 77th-Hatted Cat"
|
|
@end group
|
|
|
|
@group
|
|
(capitalize ?x)
|
|
@result{} 88
|
|
@end group
|
|
@end example
|
|
@end defun
|
|
|
|
@defun upcase-initials string-or-char
|
|
If @var{string-or-char} is a string, this function capitalizes the
|
|
initials of the words in @var{string-or-char}, without altering any
|
|
letters other than the initials. It returns a new string whose
|
|
contents are a copy of @var{string-or-char}, in which each word has
|
|
had its initial letter converted to upper 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 (@pxref{Syntax Class Table}).
|
|
|
|
When the argument to @code{upcase-initials} is a character,
|
|
@code{upcase-initials} has the same result as @code{upcase}.
|
|
|
|
@example
|
|
@group
|
|
(upcase-initials "The CAT in the hAt")
|
|
@result{} "The CAT In The HAt"
|
|
@end group
|
|
@end example
|
|
@end defun
|
|
|
|
@xref{Text Comparison}, for functions that compare strings; some of
|
|
them ignore case differences, or can optionally ignore case differences.
|
|
|
|
@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 case conversion functions for Lisp
|
|
objects (see the previous section) and those that apply to text in the
|
|
buffer (@pxref{Case Changes}). Each buffer has a case table; there is
|
|
also a standard case table which is used to initialize the case table
|
|
of new buffers.
|
|
|
|
A case table is a char-table (@pxref{Char-Tables}) whose subtype is
|
|
@code{case-table}. This char-table maps each character into the
|
|
corresponding lower case character. It has three extra slots, which
|
|
hold related tables:
|
|
|
|
@table @var
|
|
@item upcase
|
|
The upcase table maps each character into the corresponding upper
|
|
case character.
|
|
@item canonicalize
|
|
The canonicalize table maps all of a set of case-related characters
|
|
into a particular member of that set.
|
|
@item equivalences
|
|
The equivalences table maps each one of a set of case-related characters
|
|
into the next character in that set.
|
|
@end table
|
|
|
|
In simple cases, all you need to specify is the mapping to lower-case;
|
|
the three related tables will be calculated automatically from that one.
|
|
|
|
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 lower case and upper case.
|
|
|
|
The extra table @var{canonicalize} maps each character to a canonical
|
|
equivalent; any two characters that are related by case-conversion have
|
|
the same canonical equivalent character. For example, since @samp{a}
|
|
and @samp{A} are related by case-conversion, they should have the same
|
|
canonical equivalent character (which should be either @samp{a} for both
|
|
of them, or @samp{A} for both of them).
|
|
|
|
The extra table @var{equivalences} is a map that cyclically permutes
|
|
each equivalence class (of characters with the same canonical
|
|
equivalent). (For ordinary @acronym{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 slot from the lower case
|
|
and upper case mappings. You can also provide @code{nil} for
|
|
@var{equivalences}; then Emacs fills in this slot 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}.
|
|
|
|
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
|
|
be used in 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-@acronym{ASCII} character sets. They modify the specified
|
|
case table @var{case-table}; they also modify the standard syntax table.
|
|
@xref{Syntax Tables}. Normally you would use these functions to change
|
|
the standard case table.
|
|
|
|
@defun set-case-syntax-pair uc lc case-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 case-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 case-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
|
|
|
|
@ignore
|
|
arch-tag: 700b8e95-7aa5-4b52-9eb3-8f2e1ea152b4
|
|
@end ignore
|