@c -*-texinfo-*-
@c This is part of the GNU Emacs Lisp Reference Manual.
-@c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998 Free Software Foundation, Inc.
+@c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999
+@c Free Software Foundation, Inc.
@c See the file elisp.texi for copying conditions.
@setfilename ../info/strings
@node Strings and Characters, Lists, Numbers, Top
A string in Emacs 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,
+files; to send messages to users; to hold text being copied between
+buffers; and for many other purposes. Because strings are so important,
Emacs Lisp has many functions expressly for manipulating them. Emacs
Lisp programs use strings more often than individual characters.
* Creating Strings:: Functions to allocate new strings.
* Modifying Strings:: Altering the contents of an existing string.
* Text Comparison:: Comparing characters or strings.
-* String Conversion:: Converting characters or strings and vice versa.
-* Formatting Strings:: @code{format}: Emacs's analog of @code{printf}.
-* Character Case:: Case conversion functions.
-* Case Table:: Customizing case conversion.
+* String Conversion:: Converting to and from characters and strings.
+* Formatting Strings:: @code{format}: Emacs's analogue of @code{printf}.
+* Case Conversion:: Case conversion functions.
+* Case Tables:: Customizing case conversion.
@end menu
@node String Basics
@section String and Character Basics
- Strings in Emacs Lisp are arrays that contain an ordered sequence of
-characters. Characters are represented in Emacs Lisp as integers;
-whether an integer was intended as a character or not is determined only
-by how it is used. Thus, strings really contain integers.
+ Characters are represented in Emacs Lisp as integers;
+whether an integer is a character or not is determined only by how it is
+used. Thus, strings really contain integers.
The length of a string (like any array) is fixed, and cannot be
altered once the string exists. 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.)
+C are terminated by a character with @sc{ascii} code 0.)
- 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}).
+ Since strings are arrays, and therefore sequences as well, you can
+operate on them with the general array and sequence 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}).
- There are two text representations for non-@sc{ASCII} characters in
+ There are two text representations for non-@sc{ascii} characters in
Emacs strings (and in buffers): unibyte and multibyte (@pxref{Text
-Representations}). @sc{ASCII} characters always occupy one byte in a
-string; in fact, there is no real difference between the two
-representation for a string which is all @sc{ASCII}. For most Lisp
-programming, you don't need to be concerned with these two
+Representations}). An @sc{ascii} character always occupies one byte in a
+string; in fact, when a string is all @sc{ascii}, there is no real
+difference between the unibyte and multibyte representations.
+For most Lisp programming, you don't need to be concerned with these two
representations.
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.
+characters (which are large integers) rather than character
+codes 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
+modifiers; they can hold @sc{ascii} control characters, but no other
+control characters. They do not distinguish case in @sc{ascii} control
characters. If you want to store such characters in a sequence, such as
a key sequence, you must use a vector instead of a string.
-@xref{Character Type}, for more information about representation of meta
+@xref{Character Type}, for more information about the representation of meta
and other modifiers for keyboard input characters.
Strings are useful for holding regular expressions. You can also
copy them into buffers. @xref{Character Type}, and @ref{String Type},
for information about the syntax of characters and strings.
@xref{Non-ASCII Characters}, for functions to convert between text
-representations and encode and decode character codes.
+representations and to encode and decode character codes.
@node Predicates for Strings
@section The Predicates for Strings
see @ref{Sequences Arrays Vectors}, and @ref{Arrays}.
@defun stringp object
- This function returns @code{t} if @var{object} is a string, @code{nil}
+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
+This function returns @code{t} if @var{object} is a string or a
character (i.e., an integer), @code{nil} otherwise.
@end defun
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
+This function returns a string made up of @var{count} repetitions of
@var{character}. If @var{count} is negative, an error is signaled.
@example
@code{make-list} (@pxref{Building Lists}).
@end defun
-@tindex string
@defun string &rest characters
This returns a string containing the characters @var{characters}.
If the characters copied from @var{string} have text properties, the
properties are copied into the new string also. @xref{Text Properties}.
+@code{substring} also accepts a vector for the first argument.
+For example:
+
+@example
+(substring [a b (c) "d"] 1 3)
+ @result{} [b (c)]
+@end example
+
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}.
-@code{substring} actually allows vectors as well as strings for
-the first argument.
-
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
@example
(concat "abc" "-def")
@result{} "abc-def"
-(concat "abc" (list 120 (+ 256 121)) [122])
+(concat "abc" (list 120 121) [122])
@result{} "abcxyz"
;; @r{@code{nil} is an empty sequence.}
(concat "abc" nil "-def")
@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
+In Emacs versions before 21, when an argument was an integer (not a
+sequence of integers), it was converted to a string of digits making up
+the decimal printed representation of the integer. This obsolete usage
+no longer works. The proper way to convert an integer to its decimal
+printed form 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}, and @code{append} in @ref{Building
Lists}.
@end defun
-@tindex split-string
@defun split-string string separators
-Split @var{string} into substrings in between matches for the regular
+This function splits @var{string} into substrings at matches for the regular
expression @var{separators}. Each match for @var{separators} defines a
splitting point; the substrings between the splitting points are made
-into a list, which is the value. If @var{separators} is @code{nil} (or
-omitted), the default is @code{"[ \f\t\n\r\v]+"}.
+into a list, which is the value returned by @code{split-string}.
+If @var{separators} is @code{nil} (or omitted),
+the default is @code{"[ \f\t\n\r\v]+"}.
For example,
@var{idx} @var{char})} stores @var{char} into @var{string} at index
@var{idx}. Each character occupies one or more bytes, and if @var{char}
needs a different number of bytes from the character already present at
-that index, @code{aset} gets an error.
+that index, @code{aset} signals an error.
A more powerful function is @code{store-substring}:
-@tindex store-substring
@defun store-substring string idx obj
This function alters part of the contents of the string @var{string}, by
storing @var{obj} starting at index @var{idx}. The argument @var{obj}
Since it is impossible to change the length of an existing string, it is
an error if @var{obj} doesn't fit within @var{string}'s actual length,
-or if it requires a different number of bytes from the characters
-currently present at that point in @var{string}.
+or if any new character requires a different number of bytes from the
+character currently present at that point in @var{string}.
@end defun
@need 2000
@defun string= string1 string2
This function returns @code{t} if the characters of the two strings
-match exactly; case is significant.
+match exactly.
+Case is always significant, regardless of @code{case-fold-search}.
@example
(string= "abc" "abc")
strings. When @code{equal} (@pxref{Equality Predicates}) compares two
strings, it uses @code{string=}.
-If the arguments contain non-@sc{ASCII} characters, and one is unibyte
+If the strings contain non-@sc{ascii} characters, and one is unibyte
while the other is multibyte, then they cannot be equal. @xref{Text
Representations}.
@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
+This function compares two strings a character at a time. It
+scans both the strings at the same time to find the first pair of corresponding
+characters that do not match. If the lesser character of these 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
+Pairs of characters are compared according to their character codes.
+Keep in mind that lower case letters have higher numeric values in the
+@sc{ascii} character set than their upper case counterparts; digits and
many punctuation characters have a lower numeric value than upper case
-letters. A unibyte non-@sc{ASCII} character is always less than any
-multibyte non-@sc{ASCII} character (@pxref{Text Representations}).
+letters. An @sc{ascii} character is less than any non-@sc{ascii}
+character; a unibyte non-@sc{ascii} character is always less than any
+multibyte non-@sc{ascii} character (@pxref{Text Representations}).
@example
@group
@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 can be equal to
+a multibyte string. 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-ignore-case key alist
+This function works like @code{assoc}, except that @var{key} must be a
+string, and comparison is done using @code{compare-strings}, ignoring
+case differences. @xref{Association Lists}.
+@end defun
+
+@defun assoc-ignore-representation key alist
+This function works like @code{assoc}, except that @var{key} must be a
+string, and comparison is done using @code{compare-strings}.
+Case differences are significant.
@end defun
See also @code{compare-buffer-substrings} in @ref{Comparing Text}, for
@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
+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, @sc{ASCII} code
+first character of @var{string} is the null character, @sc{ascii} code
0.
@example
@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
@defun number-to-string number
@cindex integer to string
@cindex integer to decimal
-This function returns a string consisting of the printed
+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 value starts with a sign if the argument is
+point number. The returned value starts with a minus sign if the argument is
negative.
@example
See also the function @code{format} in @ref{Formatting Strings}.
@end defun
-@defun string-to-number string base
+@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}, integers are converted
in that base. If @var{base} is @code{nil}, then base ten is used.
Floating point conversion always uses base ten; we have not implemented
other radices for floating point numbers, because that would be much
-more work and does not seem useful.
+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. (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.
+and tabs.) If the first character after the ignored whitespace is
+neither a digit, 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{} 0
(string-to-number "-4.5")
@result{} -4.5
+(string-to-number "1e5")
+ @result{} 100000.0
@end example
@findex string-to-int
@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;
+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
in how they use the result of formatting.
@defun format string &rest objects
- This function returns a new string that is made by copying
+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; starting in Emacs 21, if they have
+text properties, these are copied into the output also.
@end defun
@cindex @samp{%} in format
@end example
If @var{string} contains more than one format specification, the
-format specifications correspond with successive values from
+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 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.
+ 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:
@item %s
Replace the specification with the printed representation of the object,
made without quoting (that is, using @code{princ}, not
-@code{print}---@pxref{Output Functions}). Thus, strings are represented
+@code{prin1}---@pxref{Output Functions}). Thus, strings are represented
by their contents alone, with no @samp{"} characters, and symbols appear
without @samp{\} characters.
+Starting in Emacs 21, 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.
+
If there is no corresponding object, the empty string is used.
@item %S
integer.
@item %x
+@itemx %X
@cindex integer to hexadecimal
Replace the specification with the base-sixteen representation of an
-integer.
+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 %g
Replace the specification with notation for a floating point number,
-using either exponential notation or decimal-point notation whichever
+using either exponential notation or decimal-point notation, whichever
is shorter.
@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"}.
+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
@end group
@end smallexample
-@node Character Case
+@node Case Conversion
@comment node-name, next, previous, up
-@section Character Case
+@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 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.
+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-@sc{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
-@sc{ASCII} codes 88 and 120 respectively.
+@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{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 equals the original character.
+value returned equals the original character.
@example
(upcase "The cat in the hat")
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}).
+table (@pxref{Syntax Class Table}).
When the argument to @code{capitalize} is a character, @code{capitalize}
has the same result as @code{upcase}.
@end example
@end defun
-@node Case Table
+@defun upcase-initials string
+This function capitalizes the initials of the words in @var{string},
+without altering any letters other than the initials. It returns a new
+string whose contents are a copy of @var{string}, 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}).
+
+@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 string and character case conversion
-functions (see the previous section) and those that apply to text in the
-buffer (@pxref{Case Changes}).
+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 whose subtype is @code{case-table}. This
-char-table maps each character into the corresponding lower case
-character It has three extra slots, which are related tables:
+ 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
case character.
@item canonicalize
The canonicalize table maps all of a set of case-related characters
-into some one of them.
+into a particular member of that set.
@item equivalences
-The equivalences table maps each of a set of case-related characters
-into the next one in that set.
+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 extra table @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
+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 the lower case
+@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 string from
+@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}.
- Each buffer has a case table. Emacs 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
@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.
+be used in any buffers created subsequently.
@end defun
@defun standard-case-table
@end defun
The following three functions are convenient subroutines for packages
-that define non-@sc{ASCII} character sets. They modify the specified
+that define non-@sc{ascii} character sets. They modify the specified
case table @var{case-table}; they also modify the standard syntax table.
-@xref{Syntax Tables}.
+@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
HCoop / bpt / emacs.git / blobdiff