@c -*-texinfo-*-
@c This is part of the GNU Emacs Lisp Reference Manual.
-@c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999, 2003
-@c Free Software Foundation, Inc.
+@c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999, 2001,
+@c 2002, 2003, 2004, 2005, 2006, 2007 Free Software Foundation, Inc.
@c See the file elisp.texi for copying conditions.
@setfilename ../info/strings
@node Strings and Characters, Lists, Numbers, Top
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 @acronym{ASCII} code 0.)
Since strings are arrays, and therefore sequences as well, you can
operate on them with the general array and sequence functions.
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-@acronym{ASCII} characters in
Emacs strings (and in buffers): unibyte and multibyte (@pxref{Text
-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
+Representations}). An @acronym{ASCII} character always occupies one byte in a
+string; in fact, when a string is all @acronym{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.
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 @acronym{ASCII} control characters, but no other
+control characters. They do not distinguish case in @acronym{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 the representation of meta
and other modifiers for keyboard input characters.
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.
+match regular expressions against strings with @code{string-match}
+(@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 after
+matching regular expressions against them.
Like a buffer, a string can contain text properties for the characters
in it, as well as the characters themselves. @xref{Text Properties}.
otherwise.
@end defun
+@defun string-or-null-p object
+This function returns @code{t} if @var{object} is a string or nil,
+@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 (i.e., an integer), @code{nil} otherwise.
@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
+When @code{nil} is used for @var{end}, it stands for the length of the
string. Thus,
@example
@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}.
+A @code{wrong-type-argument} error is signaled if @var{start} is not
+an integer or if @var{end} is neither an integer nor @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
beginning of a buffer is at index 1.
@end defun
+@defun substring-no-properties string &optional start end
+This works like @code{substring} but discards all text properties from
+the value. Also, @var{start} may be omitted or @code{nil}, which is
+equivalent to 0. Thus, @w{@code{(substring-no-properties
+@var{string})}} returns a copy of @var{string}, with all text
+properties removed.
+@end defun
+
@defun concat &rest sequences
@cindex copying strings
@cindex concatenating strings
Lists}.
@end defun
-@defun split-string string separators omit-nulls
+@defun split-string string &optional separators omit-nulls
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
whenever there are two consecutive matches for @var{separators}, or a
match is adjacent to the beginning or end of @var{string}. If
@var{omit-nulls} is @code{t}, these null strings are omitted from the
-result list.
+result.
If @var{separators} is @code{nil} (or omitted),
the default is the value of @code{split-string-default-separators}.
@example
(split-string " two words ")
-@result{} ("two" "words")
+ @result{} ("two" "words")
@end example
-The result is not @samp{("" "two" "words" "")}, which would rarely be
-useful. If you need such a result, use an explict value for
+The result is not @code{("" "two" "words" "")}, which would rarely be
+useful. If you need such a result, use an explicit value for
@var{separators}:
@example
-(split-string " two words " split-string-default-separators)
-@result{} ("" "two" "words" "")
+(split-string " two words "
+ split-string-default-separators)
+ @result{} ("" "two" "words" "")
@end example
More examples:
@example
(split-string "Soup is good food" "o")
-@result{} ("S" "up is g" "" "d f" "" "d")
+ @result{} ("S" "up is g" "" "d f" "" "d")
(split-string "Soup is good food" "o" t)
-@result{} ("S" "up is g" "d f" "d")
+ @result{} ("S" "up is g" "d f" "d")
(split-string "Soup is good food" "o+")
-@result{} ("S" "up is g" "d f" "d")
+ @result{} ("S" "up is g" "d f" "d")
+@end example
+
+Empty matches do count, except that @code{split-string} will not look
+for a final empty match when it already reached the end of the string
+using a non-empty match or when @var{string} is empty:
+
+@example
+(split-string "aooob" "o*")
+ @result{} ("" "a" "" "b" "")
+(split-string "ooaboo" "o*")
+ @result{} ("" "" "a" "b" "")
+(split-string "" "")
+ @result{} ("")
+@end example
+
+However, when @var{separators} can match the empty string,
+@var{omit-nulls} is usually @code{t}, so that the subtleties in the
+three previous examples are rarely relevant:
+
+@example
+(split-string "Soup is good food" "o*" t)
+ @result{} ("S" "u" "p" " " "i" "s" " " "g" "d" " " "f" "d")
+(split-string "Nice doggy!" "" t)
+ @result{} ("N" "i" "c" "e" " " "d" "o" "g" "g" "y" "!")
+(split-string "" "" t)
+ @result{} nil
@end example
-Empty matches do count, when not adjacent to another match:
+Somewhat odd, but predictable, behavior can occur for certain
+``non-greedy'' values of @var{separators} that can prefer empty
+matches over non-empty matches. Again, such values rarely occur in
+practice:
@example
-(split-string "Soup is good food" "o*")
-@result{}("S" "u" "p" " " "i" "s" " " "g" "d" " " "f" "d")
-(split-string "Nice doggy!" "")
-@result{}("N" "i" "c" "e" " " "d" "o" "g" "g" "y" "!")
+(split-string "ooo" "o*" t)
+ @result{} nil
+(split-string "ooo" "\\|o+" t)
+ @result{} ("o" "o" "o")
@end example
@end defun
@defvar split-string-default-separators
-The default value of @var{separators} for @code{split-string}, initially
-@samp{"[ \f\t\n\r\v]+"}.
+The default value of @var{separators} for @code{split-string}. Its
+usual value is @w{@code{"[ \f\t\n\r\v]+"}}.
@end defvar
@node Modifying Strings
an error if @var{obj} doesn't fit within @var{string}'s actual length,
or if any new character requires a different number of bytes from the
character currently present at that point in @var{string}.
+@end defun
+
+ To clear out a string that contained a password, use
+@code{clear-string}:
+
+@defun clear-string string
+This makes @var{string} a unibyte string and clears its contents to
+zeros. It may also change @var{string}'s length.
@end defun
@need 2000
@defun string= string1 string2
This function returns @code{t} if the characters of the two strings
-match exactly.
+match exactly. Symbols are also allowed as arguments, in which case
+their print names are used.
Case is always significant, regardless of @code{case-fold-search}.
@example
strings. When @code{equal} (@pxref{Equality Predicates}) compares two
strings, it uses @code{string=}.
-If the strings contain non-@sc{ascii} characters, and one is unibyte
-while the other is multibyte, then they cannot be equal. @xref{Text
+For technical reasons, a unibyte and a multibyte string are
+@code{equal} if and only if they contain the same sequence of
+character codes and all these codes are either in the range 0 through
+127 (@acronym{ASCII}) or 160 through 255 (@code{eight-bit-graphic}).
+However, when a unibyte string gets converted to a multibyte string,
+all characters with codes in the range 160 through 255 get converted
+to characters with higher codes, whereas @acronym{ASCII} characters
+remain unchanged. Thus, a unibyte string and its conversion to
+multibyte are only @code{equal} if the string is all @acronym{ASCII}.
+Character codes 160 through 255 are not entirely proper in multibyte
+text, even though they can occur. As a consequence, the situation
+where a unibyte and a multibyte string are @code{equal} without both
+being all @acronym{ASCII} is a technical oddity that very few Emacs
+Lisp programmers ever get confronted with. @xref{Text
Representations}.
@end defun
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
+@acronym{ASCII} character set than their upper case counterparts; digits and
many punctuation characters have a lower numeric value than upper case
-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}).
+letters. An @acronym{ASCII} character is less than any non-@acronym{ASCII}
+character; a unibyte non-@acronym{ASCII} character is always less than any
+multibyte non-@acronym{ASCII} character (@pxref{Text Representations}).
@example
@group
@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
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.
+(@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
portion) is less.
@end defun
-@defun assoc-ignore-case key alist
+@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}, ignoring
-case differences. @xref{Association Lists}.
+string or symbol, and comparison is done using @code{compare-strings}.
+Symbols are converted to strings before testing.
+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 or symbols rather than conses. In particular, @var{alist} can
+be a list of strings or symbols rather than an actual alist.
+@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
-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}.
+ See also the @code{compare-buffer-substrings} function 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
@cindex conversion of strings
This section describes functions for conversions between characters,
-strings and integers. @code{format} and @code{prin1-to-string}
+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
@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.
+are used primarily for making help messages.
@defun char-to-string character
@cindex character to 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, @acronym{ASCII} code
0.
@example
@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
@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. If @var{string} looks like an
-integer but its value is too large to fit into a Lisp integer,
+@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. (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, nor a plus or minus sign, nor the leading dot of a
-floating point number, this function returns 0.
+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")
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.
+are copied directly into the output, including their text properties,
+if any.
@end defun
@cindex @samp{%} in format
@end group
@end example
+ Since @code{format} interprets @samp{%} characters as format
+specifications, you should @emph{never} pass an arbitrary string as
+the first argument. This is particularly true when the string is
+generated by some Lisp code. Unless the string is @emph{known} to
+never include any @samp{%} characters, pass @code{"%s"}, described
+below, as the first argument, and the string as the second, like this:
+
+@example
+ (format "%s" @var{arbitrary-string})
+@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 unpredictable
-behavior. Any extra values to be formatted are ignored.
+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
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
+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
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.
-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
@end group
@end example
-@cindex numeric prefix
@cindex field width
@cindex padding
- All the specification characters allow an optional numeric prefix
-between the @samp{%} and the character. 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 on the left if the prefix is positive (or starts with
-zero) and on the right if the prefix is negative. The padding character
-is normally a space, but if the numeric prefix starts with a zero, zeros
-are used for padding. Here are some examples of 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{} "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.
+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
@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, a plus character
+inserts a plus sign (otherwise nothing is inserted for positive
+numbers). These flags are ignored except for @samp{%d}, @samp{%e},
+@samp{%f}, @samp{%g}, and if both flags are present the space is
+ignored.
+
+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
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-@sc{ascii} letters); other
+@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}).
arguments.
The examples below use the characters @samp{X} and @samp{x} which have
-@sc{ascii} codes 88 and 120 respectively.
+@acronym{ASCII} codes 88 and 120 respectively.
@defun downcase string-or-char
This function converts a character or a string to lower case.
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)
@end example
@end defun
-@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
+@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")
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 cyclicly permutes
+ The extra table @var{equivalences} is a map that cyclically permutes
each equivalence class (of characters with the same canonical
-equivalent). (For ordinary @sc{ascii}, this would map @samp{a} into
+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.)
@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-@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.
HCoop / bpt / emacs.git / blobdiff