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diff --git a/lispref/nonascii.texi b/lispref/nonascii.texi deleted file mode 100644 index 0922db4fac4..00000000000 --- a/lispref/nonascii.texi +++ /dev/null @@ -1,1501 +0,0 @@ -@c -*-texinfo-*- -@c This is part of the GNU Emacs Lisp Reference Manual. -@c Copyright (C) 1998, 1999, 2001, 2002, 2003, 2004, -@c 2005, 2006, 2007, 2008 Free Software Foundation, Inc. -@c See the file elisp.texi for copying conditions. -@setfilename ../info/characters -@node Non-ASCII Characters, Searching and Matching, Text, Top -@chapter Non-@acronym{ASCII} Characters -@cindex multibyte characters -@cindex characters, multi-byte -@cindex non-@acronym{ASCII} characters - - This chapter covers the special issues relating to non-@acronym{ASCII} -characters and how they are stored in strings and buffers. - -@menu -* Text Representations:: Unibyte and multibyte representations -* Converting Representations:: Converting unibyte to multibyte and vice versa. -* Selecting a Representation:: Treating a byte sequence as unibyte or multi. -* Character Codes:: How unibyte and multibyte relate to - codes of individual characters. -* Character Sets:: The space of possible character codes - is divided into various character sets. -* Chars and Bytes:: More information about multibyte encodings. -* Splitting Characters:: Converting a character to its byte sequence. -* Scanning Charsets:: Which character sets are used in a buffer? -* Translation of Characters:: Translation tables are used for conversion. -* Coding Systems:: Coding systems are conversions for saving files. -* Input Methods:: Input methods allow users to enter various - non-ASCII characters without special keyboards. -* Locales:: Interacting with the POSIX locale. -@end menu - -@node Text Representations -@section Text Representations -@cindex text representations - - Emacs has two @dfn{text representations}---two ways to represent text -in a string or buffer. These are called @dfn{unibyte} and -@dfn{multibyte}. Each string, and each buffer, uses one of these two -representations. For most purposes, you can ignore the issue of -representations, because Emacs converts text between them as -appropriate. Occasionally in Lisp programming you will need to pay -attention to the difference. - -@cindex unibyte text - In unibyte representation, each character occupies one byte and -therefore the possible character codes range from 0 to 255. Codes 0 -through 127 are @acronym{ASCII} characters; the codes from 128 through 255 -are used for one non-@acronym{ASCII} character set (you can choose which -character set by setting the variable @code{nonascii-insert-offset}). - -@cindex leading code -@cindex multibyte text -@cindex trailing codes - In multibyte representation, a character may occupy more than one -byte, and as a result, the full range of Emacs character codes can be -stored. The first byte of a multibyte character is always in the range -128 through 159 (octal 0200 through 0237). These values are called -@dfn{leading codes}. The second and subsequent bytes of a multibyte -character are always in the range 160 through 255 (octal 0240 through -0377); these values are @dfn{trailing codes}. - - Some sequences of bytes are not valid in multibyte text: for example, -a single isolated byte in the range 128 through 159 is not allowed. But -character codes 128 through 159 can appear in multibyte text, -represented as two-byte sequences. All the character codes 128 through -255 are possible (though slightly abnormal) in multibyte text; they -appear in multibyte buffers and strings when you do explicit encoding -and decoding (@pxref{Explicit Encoding}). - - In a buffer, the buffer-local value of the variable -@code{enable-multibyte-characters} specifies the representation used. -The representation for a string is determined and recorded in the string -when the string is constructed. - -@defvar enable-multibyte-characters -This variable specifies the current buffer's text representation. -If it is non-@code{nil}, the buffer contains multibyte text; otherwise, -it contains unibyte text. - -You cannot set this variable directly; instead, use the function -@code{set-buffer-multibyte} to change a buffer's representation. -@end defvar - -@defvar default-enable-multibyte-characters -This variable's value is entirely equivalent to @code{(default-value -'enable-multibyte-characters)}, and setting this variable changes that -default value. Setting the local binding of -@code{enable-multibyte-characters} in a specific buffer is not allowed, -but changing the default value is supported, and it is a reasonable -thing to do, because it has no effect on existing buffers. - -The @samp{--unibyte} command line option does its job by setting the -default value to @code{nil} early in startup. -@end defvar - -@defun position-bytes position -Return the byte-position corresponding to buffer position -@var{position} in the current buffer. This is 1 at the start of the -buffer, and counts upward in bytes. If @var{position} is out of -range, the value is @code{nil}. -@end defun - -@defun byte-to-position byte-position -Return the buffer position corresponding to byte-position -@var{byte-position} in the current buffer. If @var{byte-position} is -out of range, the value is @code{nil}. -@end defun - -@defun multibyte-string-p string -Return @code{t} if @var{string} is a multibyte string. -@end defun - -@defun string-bytes string -@cindex string, number of bytes -This function returns the number of bytes in @var{string}. -If @var{string} is a multibyte string, this can be greater than -@code{(length @var{string})}. -@end defun - -@node Converting Representations -@section Converting Text Representations - - Emacs can convert unibyte text to multibyte; it can also convert -multibyte text to unibyte, though this conversion loses information. In -general these conversions happen when inserting text into a buffer, or -when putting text from several strings together in one string. You can -also explicitly convert a string's contents to either representation. - - Emacs chooses the representation for a string based on the text that -it is constructed from. The general rule is to convert unibyte text to -multibyte text when combining it with other multibyte text, because the -multibyte representation is more general and can hold whatever -characters the unibyte text has. - - When inserting text into a buffer, Emacs converts the text to the -buffer's representation, as specified by -@code{enable-multibyte-characters} in that buffer. In particular, when -you insert multibyte text into a unibyte buffer, Emacs converts the text -to unibyte, even though this conversion cannot in general preserve all -the characters that might be in the multibyte text. The other natural -alternative, to convert the buffer contents to multibyte, is not -acceptable because the buffer's representation is a choice made by the -user that cannot be overridden automatically. - - Converting unibyte text to multibyte text leaves @acronym{ASCII} characters -unchanged, and likewise character codes 128 through 159. It converts -the non-@acronym{ASCII} codes 160 through 255 by adding the value -@code{nonascii-insert-offset} to each character code. By setting this -variable, you specify which character set the unibyte characters -correspond to (@pxref{Character Sets}). For example, if -@code{nonascii-insert-offset} is 2048, which is @code{(- (make-char -'latin-iso8859-1) 128)}, then the unibyte non-@acronym{ASCII} characters -correspond to Latin 1. If it is 2688, which is @code{(- (make-char -'greek-iso8859-7) 128)}, then they correspond to Greek letters. - - Converting multibyte text to unibyte is simpler: it discards all but -the low 8 bits of each character code. If @code{nonascii-insert-offset} -has a reasonable value, corresponding to the beginning of some character -set, this conversion is the inverse of the other: converting unibyte -text to multibyte and back to unibyte reproduces the original unibyte -text. - -@defvar nonascii-insert-offset -This variable specifies the amount to add to a non-@acronym{ASCII} character -when converting unibyte text to multibyte. It also applies when -@code{self-insert-command} inserts a character in the unibyte -non-@acronym{ASCII} range, 128 through 255. However, the functions -@code{insert} and @code{insert-char} do not perform this conversion. - -The right value to use to select character set @var{cs} is @code{(- -(make-char @var{cs}) 128)}. If the value of -@code{nonascii-insert-offset} is zero, then conversion actually uses the -value for the Latin 1 character set, rather than zero. -@end defvar - -@defvar nonascii-translation-table -This variable provides a more general alternative to -@code{nonascii-insert-offset}. You can use it to specify independently -how to translate each code in the range of 128 through 255 into a -multibyte character. The value should be a char-table, or @code{nil}. -If this is non-@code{nil}, it overrides @code{nonascii-insert-offset}. -@end defvar - -The next three functions either return the argument @var{string}, or a -newly created string with no text properties. - -@defun string-make-unibyte string -This function converts the text of @var{string} to unibyte -representation, if it isn't already, and returns the result. If -@var{string} is a unibyte string, it is returned unchanged. Multibyte -character codes are converted to unibyte according to -@code{nonascii-translation-table} or, if that is @code{nil}, using -@code{nonascii-insert-offset}. If the lookup in the translation table -fails, this function takes just the low 8 bits of each character. -@end defun - -@defun string-make-multibyte string -This function converts the text of @var{string} to multibyte -representation, if it isn't already, and returns the result. If -@var{string} is a multibyte string or consists entirely of -@acronym{ASCII} characters, it is returned unchanged. In particular, -if @var{string} is unibyte and entirely @acronym{ASCII}, the returned -string is unibyte. (When the characters are all @acronym{ASCII}, -Emacs primitives will treat the string the same way whether it is -unibyte or multibyte.) If @var{string} is unibyte and contains -non-@acronym{ASCII} characters, the function -@code{unibyte-char-to-multibyte} is used to convert each unibyte -character to a multibyte character. -@end defun - -@defun string-to-multibyte string -This function returns a multibyte string containing the same sequence -of character codes as @var{string}. Unlike -@code{string-make-multibyte}, this function unconditionally returns a -multibyte string. If @var{string} is a multibyte string, it is -returned unchanged. -@end defun - -@defun multibyte-char-to-unibyte char -This convert the multibyte character @var{char} to a unibyte -character, based on @code{nonascii-translation-table} and -@code{nonascii-insert-offset}. -@end defun - -@defun unibyte-char-to-multibyte char -This convert the unibyte character @var{char} to a multibyte -character, based on @code{nonascii-translation-table} and -@code{nonascii-insert-offset}. -@end defun - -@node Selecting a Representation -@section Selecting a Representation - - Sometimes it is useful to examine an existing buffer or string as -multibyte when it was unibyte, or vice versa. - -@defun set-buffer-multibyte multibyte -Set the representation type of the current buffer. If @var{multibyte} -is non-@code{nil}, the buffer becomes multibyte. If @var{multibyte} -is @code{nil}, the buffer becomes unibyte. - -This function leaves the buffer contents unchanged when viewed as a -sequence of bytes. As a consequence, it can change the contents viewed -as characters; a sequence of two bytes which is treated as one character -in multibyte representation will count as two characters in unibyte -representation. Character codes 128 through 159 are an exception. They -are represented by one byte in a unibyte buffer, but when the buffer is -set to multibyte, they are converted to two-byte sequences, and vice -versa. - -This function sets @code{enable-multibyte-characters} to record which -representation is in use. It also adjusts various data in the buffer -(including overlays, text properties and markers) so that they cover the -same text as they did before. - -You cannot use @code{set-buffer-multibyte} on an indirect buffer, -because indirect buffers always inherit the representation of the -base buffer. -@end defun - -@defun string-as-unibyte string -This function returns a string with the same bytes as @var{string} but -treating each byte as a character. This means that the value may have -more characters than @var{string} has. - -If @var{string} is already a unibyte string, then the value is -@var{string} itself. Otherwise it is a newly created string, with no -text properties. If @var{string} is multibyte, any characters it -contains of charset @code{eight-bit-control} or @code{eight-bit-graphic} -are converted to the corresponding single byte. -@end defun - -@defun string-as-multibyte string -This function returns a string with the same bytes as @var{string} but -treating each multibyte sequence as one character. This means that the -value may have fewer characters than @var{string} has. - -If @var{string} is already a multibyte string, then the value is -@var{string} itself. Otherwise it is a newly created string, with no -text properties. If @var{string} is unibyte and contains any individual -8-bit bytes (i.e.@: not part of a multibyte form), they are converted to -the corresponding multibyte character of charset @code{eight-bit-control} -or @code{eight-bit-graphic}. -@end defun - -@node Character Codes -@section Character Codes -@cindex character codes - - The unibyte and multibyte text representations use different character -codes. The valid character codes for unibyte representation range from -0 to 255---the values that can fit in one byte. The valid character -codes for multibyte representation range from 0 to 524287, but not all -values in that range are valid. The values 128 through 255 are not -entirely proper in multibyte text, but they can occur if you do explicit -encoding and decoding (@pxref{Explicit Encoding}). Some other character -codes cannot occur at all in multibyte text. Only the @acronym{ASCII} codes -0 through 127 are completely legitimate in both representations. - -@defun char-valid-p charcode &optional genericp -This returns @code{t} if @var{charcode} is valid (either for unibyte -text or for multibyte text). - -@example -(char-valid-p 65) - @result{} t -(char-valid-p 256) - @result{} nil -(char-valid-p 2248) - @result{} t -@end example - -If the optional argument @var{genericp} is non-@code{nil}, this -function also returns @code{t} if @var{charcode} is a generic -character (@pxref{Splitting Characters}). -@end defun - -@node Character Sets -@section Character Sets -@cindex character sets - - Emacs classifies characters into various @dfn{character sets}, each of -which has a name which is a symbol. Each character belongs to one and -only one character set. - - In general, there is one character set for each distinct script. For -example, @code{latin-iso8859-1} is one character set, -@code{greek-iso8859-7} is another, and @code{ascii} is another. An -Emacs character set can hold at most 9025 characters; therefore, in some -cases, characters that would logically be grouped together are split -into several character sets. For example, one set of Chinese -characters, generally known as Big 5, is divided into two Emacs -character sets, @code{chinese-big5-1} and @code{chinese-big5-2}. - - @acronym{ASCII} characters are in character set @code{ascii}. The -non-@acronym{ASCII} characters 128 through 159 are in character set -@code{eight-bit-control}, and codes 160 through 255 are in character set -@code{eight-bit-graphic}. - -@defun charsetp object -Returns @code{t} if @var{object} is a symbol that names a character set, -@code{nil} otherwise. -@end defun - -@defvar charset-list -The value is a list of all defined character set names. -@end defvar - -@defun charset-list -This function returns the value of @code{charset-list}. It is only -provided for backward compatibility. -@end defun - -@defun char-charset character -This function returns the name of the character set that @var{character} -belongs to, or the symbol @code{unknown} if @var{character} is not a -valid character. -@end defun - -@defun charset-plist charset -This function returns the charset property list of the character set -@var{charset}. Although @var{charset} is a symbol, this is not the same -as the property list of that symbol. Charset properties are used for -special purposes within Emacs. -@end defun - -@deffn Command list-charset-chars charset -This command displays a list of characters in the character set -@var{charset}. -@end deffn - -@node Chars and Bytes -@section Characters and Bytes -@cindex bytes and characters - -@cindex introduction sequence (of character) -@cindex dimension (of character set) - In multibyte representation, each character occupies one or more -bytes. Each character set has an @dfn{introduction sequence}, which is -normally one or two bytes long. (Exception: the @code{ascii} character -set and the @code{eight-bit-graphic} character set have a zero-length -introduction sequence.) The introduction sequence is the beginning of -the byte sequence for any character in the character set. The rest of -the character's bytes distinguish it from the other characters in the -same character set. Depending on the character set, there are either -one or two distinguishing bytes; the number of such bytes is called the -@dfn{dimension} of the character set. - -@defun charset-dimension charset -This function returns the dimension of @var{charset}; at present, the -dimension is always 1 or 2. -@end defun - -@defun charset-bytes charset -This function returns the number of bytes used to represent a character -in character set @var{charset}. -@end defun - - This is the simplest way to determine the byte length of a character -set's introduction sequence: - -@example -(- (charset-bytes @var{charset}) - (charset-dimension @var{charset})) -@end example - -@node Splitting Characters -@section Splitting Characters -@cindex character as bytes - - The functions in this section convert between characters and the byte -values used to represent them. For most purposes, there is no need to -be concerned with the sequence of bytes used to represent a character, -because Emacs translates automatically when necessary. - -@defun split-char character -Return a list containing the name of the character set of -@var{character}, followed by one or two byte values (integers) which -identify @var{character} within that character set. The number of byte -values is the character set's dimension. - -If @var{character} is invalid as a character code, @code{split-char} -returns a list consisting of the symbol @code{unknown} and @var{character}. - -@example -(split-char 2248) - @result{} (latin-iso8859-1 72) -(split-char 65) - @result{} (ascii 65) -(split-char 128) - @result{} (eight-bit-control 128) -@end example -@end defun - -@cindex generate characters in charsets -@defun make-char charset &optional code1 code2 -This function returns the character in character set @var{charset} whose -position codes are @var{code1} and @var{code2}. This is roughly the -inverse of @code{split-char}. Normally, you should specify either one -or both of @var{code1} and @var{code2} according to the dimension of -@var{charset}. For example, - -@example -(make-char 'latin-iso8859-1 72) - @result{} 2248 -@end example - -Actually, the eighth bit of both @var{code1} and @var{code2} is zeroed -before they are used to index @var{charset}. Thus you may use, for -instance, an ISO 8859 character code rather than subtracting 128, as -is necessary to index the corresponding Emacs charset. -@end defun - -@cindex generic characters - If you call @code{make-char} with no @var{byte-values}, the result is -a @dfn{generic character} which stands for @var{charset}. A generic -character is an integer, but it is @emph{not} valid for insertion in the -buffer as a character. It can be used in @code{char-table-range} to -refer to the whole character set (@pxref{Char-Tables}). -@code{char-valid-p} returns @code{nil} for generic characters. -For example: - -@example -(make-char 'latin-iso8859-1) - @result{} 2176 -(char-valid-p 2176) - @result{} nil -(char-valid-p 2176 t) - @result{} t -(split-char 2176) - @result{} (latin-iso8859-1 0) -@end example - -The character sets @code{ascii}, @code{eight-bit-control}, and -@code{eight-bit-graphic} don't have corresponding generic characters. If -@var{charset} is one of them and you don't supply @var{code1}, -@code{make-char} returns the character code corresponding to the -smallest code in @var{charset}. - -@node Scanning Charsets -@section Scanning for Character Sets - - Sometimes it is useful to find out which character sets appear in a -part of a buffer or a string. One use for this is in determining which -coding systems (@pxref{Coding Systems}) are capable of representing all -of the text in question. - -@defun charset-after &optional pos -This function return the charset of a character in the current buffer -at position @var{pos}. If @var{pos} is omitted or @code{nil}, it -defaults to the current value of point. If @var{pos} is out of range, -the value is @code{nil}. -@end defun - -@defun find-charset-region beg end &optional translation -This function returns a list of the character sets that appear in the -current buffer between positions @var{beg} and @var{end}. - -The optional argument @var{translation} specifies a translation table to -be used in scanning the text (@pxref{Translation of Characters}). If it -is non-@code{nil}, then each character in the region is translated -through this table, and the value returned describes the translated -characters instead of the characters actually in the buffer. -@end defun - -@defun find-charset-string string &optional translation -This function returns a list of the character sets that appear in the -string @var{string}. It is just like @code{find-charset-region}, except -that it applies to the contents of @var{string} instead of part of the -current buffer. -@end defun - -@node Translation of Characters -@section Translation of Characters -@cindex character translation tables -@cindex translation tables - - A @dfn{translation table} is a char-table that specifies a mapping -of characters into characters. These tables are used in encoding and -decoding, and for other purposes. Some coding systems specify their -own particular translation tables; there are also default translation -tables which apply to all other coding systems. - - For instance, the coding-system @code{utf-8} has a translation table -that maps characters of various charsets (e.g., -@code{latin-iso8859-@var{x}}) into Unicode character sets. This way, -it can encode Latin-2 characters into UTF-8. Meanwhile, -@code{unify-8859-on-decoding-mode} operates by specifying -@code{standard-translation-table-for-decode} to translate -Latin-@var{x} characters into corresponding Unicode characters. - -@defun make-translation-table &rest translations -This function returns a translation table based on the argument -@var{translations}. Each element of @var{translations} should be a -list of elements of the form @code{(@var{from} . @var{to})}; this says -to translate the character @var{from} into @var{to}. - -The arguments and the forms in each argument are processed in order, -and if a previous form already translates @var{to} to some other -character, say @var{to-alt}, @var{from} is also translated to -@var{to-alt}. - -You can also map one whole character set into another character set with -the same dimension. To do this, you specify a generic character (which -designates a character set) for @var{from} (@pxref{Splitting Characters}). -In this case, if @var{to} is also a generic character, its character -set should have the same dimension as @var{from}'s. Then the -translation table translates each character of @var{from}'s character -set into the corresponding character of @var{to}'s character set. If -@var{from} is a generic character and @var{to} is an ordinary -character, then the translation table translates every character of -@var{from}'s character set into @var{to}. -@end defun - - In decoding, the translation table's translations are applied to the -characters that result from ordinary decoding. If a coding system has -property @code{translation-table-for-decode}, that specifies the -translation table to use. (This is a property of the coding system, -as returned by @code{coding-system-get}, not a property of the symbol -that is the coding system's name. @xref{Coding System Basics,, Basic -Concepts of Coding Systems}.) Otherwise, if -@code{standard-translation-table-for-decode} is non-@code{nil}, -decoding uses that table. - - In encoding, the translation table's translations are applied to the -characters in the buffer, and the result of translation is actually -encoded. If a coding system has property -@code{translation-table-for-encode}, that specifies the translation -table to use. Otherwise the variable -@code{standard-translation-table-for-encode} specifies the translation -table. - -@defvar standard-translation-table-for-decode -This is the default translation table for decoding, for -coding systems that don't specify any other translation table. -@end defvar - -@defvar standard-translation-table-for-encode -This is the default translation table for encoding, for -coding systems that don't specify any other translation table. -@end defvar - -@defvar translation-table-for-input -Self-inserting characters are translated through this translation -table before they are inserted. Search commands also translate their -input through this table, so they can compare more reliably with -what's in the buffer. - -@code{set-buffer-file-coding-system} sets this variable so that your -keyboard input gets translated into the character sets that the buffer -is likely to contain. This variable automatically becomes -buffer-local when set. -@end defvar - -@node Coding Systems -@section Coding Systems - -@cindex coding system - When Emacs reads or writes a file, and when Emacs sends text to a -subprocess or receives text from a subprocess, it normally performs -character code conversion and end-of-line conversion as specified -by a particular @dfn{coding system}. - - How to define a coding system is an arcane matter, and is not -documented here. - -@menu -* Coding System Basics:: Basic concepts. -* Encoding and I/O:: How file I/O functions handle coding systems. -* Lisp and Coding Systems:: Functions to operate on coding system names. -* User-Chosen Coding Systems:: Asking the user to choose a coding system. -* Default Coding Systems:: Controlling the default choices. -* Specifying Coding Systems:: Requesting a particular coding system - for a single file operation. -* Explicit Encoding:: Encoding or decoding text without doing I/O. -* Terminal I/O Encoding:: Use of encoding for terminal I/O. -* MS-DOS File Types:: How DOS "text" and "binary" files - relate to coding systems. -@end menu - -@node Coding System Basics -@subsection Basic Concepts of Coding Systems - -@cindex character code conversion - @dfn{Character code conversion} involves conversion between the encoding -used inside Emacs and some other encoding. Emacs supports many -different encodings, in that it can convert to and from them. For -example, it can convert text to or from encodings such as Latin 1, Latin -2, Latin 3, Latin 4, Latin 5, and several variants of ISO 2022. In some -cases, Emacs supports several alternative encodings for the same -characters; for example, there are three coding systems for the Cyrillic -(Russian) alphabet: ISO, Alternativnyj, and KOI8. - - Most coding systems specify a particular character code for -conversion, but some of them leave the choice unspecified---to be chosen -heuristically for each file, based on the data. - - In general, a coding system doesn't guarantee roundtrip identity: -decoding a byte sequence using coding system, then encoding the -resulting text in the same coding system, can produce a different byte -sequence. However, the following coding systems do guarantee that the -byte sequence will be the same as what you originally decoded: - -@quotation -chinese-big5 chinese-iso-8bit cyrillic-iso-8bit emacs-mule -greek-iso-8bit hebrew-iso-8bit iso-latin-1 iso-latin-2 iso-latin-3 -iso-latin-4 iso-latin-5 iso-latin-8 iso-latin-9 iso-safe -japanese-iso-8bit japanese-shift-jis korean-iso-8bit raw-text -@end quotation - - Encoding buffer text and then decoding the result can also fail to -reproduce the original text. For instance, if you encode Latin-2 -characters with @code{utf-8} and decode the result using the same -coding system, you'll get Unicode characters (of charset -@code{mule-unicode-0100-24ff}). If you encode Unicode characters with -@code{iso-latin-2} and decode the result with the same coding system, -you'll get Latin-2 characters. - -@cindex EOL conversion -@cindex end-of-line conversion -@cindex line end conversion - @dfn{End of line conversion} handles three different conventions used -on various systems for representing end of line in files. The Unix -convention is to use the linefeed character (also called newline). The -DOS convention is to use a carriage-return and a linefeed at the end of -a line. The Mac convention is to use just carriage-return. - -@cindex base coding system -@cindex variant coding system - @dfn{Base coding systems} such as @code{latin-1} leave the end-of-line -conversion unspecified, to be chosen based on the data. @dfn{Variant -coding systems} such as @code{latin-1-unix}, @code{latin-1-dos} and -@code{latin-1-mac} specify the end-of-line conversion explicitly as -well. Most base coding systems have three corresponding variants whose -names are formed by adding @samp{-unix}, @samp{-dos} and @samp{-mac}. - - The coding system @code{raw-text} is special in that it prevents -character code conversion, and causes the buffer visited with that -coding system to be a unibyte buffer. It does not specify the -end-of-line conversion, allowing that to be determined as usual by the -data, and has the usual three variants which specify the end-of-line -conversion. @code{no-conversion} is equivalent to @code{raw-text-unix}: -it specifies no conversion of either character codes or end-of-line. - - The coding system @code{emacs-mule} specifies that the data is -represented in the internal Emacs encoding. This is like -@code{raw-text} in that no code conversion happens, but different in -that the result is multibyte data. - -@defun coding-system-get coding-system property -This function returns the specified property of the coding system -@var{coding-system}. Most coding system properties exist for internal -purposes, but one that you might find useful is @code{mime-charset}. -That property's value is the name used in MIME for the character coding -which this coding system can read and write. Examples: - -@example -(coding-system-get 'iso-latin-1 'mime-charset) - @result{} iso-8859-1 -(coding-system-get 'iso-2022-cn 'mime-charset) - @result{} iso-2022-cn -(coding-system-get 'cyrillic-koi8 'mime-charset) - @result{} koi8-r -@end example - -The value of the @code{mime-charset} property is also defined -as an alias for the coding system. -@end defun - -@node Encoding and I/O -@subsection Encoding and I/O - - The principal purpose of coding systems is for use in reading and -writing files. The function @code{insert-file-contents} uses -a coding system for decoding the file data, and @code{write-region} -uses one to encode the buffer contents. - - You can specify the coding system to use either explicitly -(@pxref{Specifying Coding Systems}), or implicitly using a default -mechanism (@pxref{Default Coding Systems}). But these methods may not -completely specify what to do. For example, they may choose a coding -system such as @code{undefined} which leaves the character code -conversion to be determined from the data. In these cases, the I/O -operation finishes the job of choosing a coding system. Very often -you will want to find out afterwards which coding system was chosen. - -@defvar buffer-file-coding-system -This buffer-local variable records the coding system that was used to visit -the current buffer. It is used for saving the buffer, and for writing part -of the buffer with @code{write-region}. If the text to be written -cannot be safely encoded using the coding system specified by this -variable, these operations select an alternative encoding by calling -the function @code{select-safe-coding-system} (@pxref{User-Chosen -Coding Systems}). If selecting a different encoding requires to ask -the user to specify a coding system, @code{buffer-file-coding-system} -is updated to the newly selected coding system. - -@code{buffer-file-coding-system} does @emph{not} affect sending text -to a subprocess. -@end defvar - -@defvar save-buffer-coding-system -This variable specifies the coding system for saving the buffer (by -overriding @code{buffer-file-coding-system}). Note that it is not used -for @code{write-region}. - -When a command to save the buffer starts out to use -@code{buffer-file-coding-system} (or @code{save-buffer-coding-system}), -and that coding system cannot handle -the actual text in the buffer, the command asks the user to choose -another coding system (by calling @code{select-safe-coding-system}). -After that happens, the command also updates -@code{buffer-file-coding-system} to represent the coding system that -the user specified. -@end defvar - -@defvar last-coding-system-used -I/O operations for files and subprocesses set this variable to the -coding system name that was used. The explicit encoding and decoding -functions (@pxref{Explicit Encoding}) set it too. - -@strong{Warning:} Since receiving subprocess output sets this variable, -it can change whenever Emacs waits; therefore, you should copy the -value shortly after the function call that stores the value you are -interested in. -@end defvar - - The variable @code{selection-coding-system} specifies how to encode -selections for the window system. @xref{Window System Selections}. - -@defvar file-name-coding-system -The variable @code{file-name-coding-system} specifies the coding -system to use for encoding file names. Emacs encodes file names using -that coding system for all file operations. If -@code{file-name-coding-system} is @code{nil}, Emacs uses a default -coding system determined by the selected language environment. In the -default language environment, any non-@acronym{ASCII} characters in -file names are not encoded specially; they appear in the file system -using the internal Emacs representation. -@end defvar - - @strong{Warning:} if you change @code{file-name-coding-system} (or -the language environment) in the middle of an Emacs session, problems -can result if you have already visited files whose names were encoded -using the earlier coding system and are handled differently under the -new coding system. If you try to save one of these buffers under the -visited file name, saving may use the wrong file name, or it may get -an error. If such a problem happens, use @kbd{C-x C-w} to specify a -new file name for that buffer. - -@node Lisp and Coding Systems -@subsection Coding Systems in Lisp - - Here are the Lisp facilities for working with coding systems: - -@defun coding-system-list &optional base-only -This function returns a list of all coding system names (symbols). If -@var{base-only} is non-@code{nil}, the value includes only the -base coding systems. Otherwise, it includes alias and variant coding -systems as well. -@end defun - -@defun coding-system-p object -This function returns @code{t} if @var{object} is a coding system -name or @code{nil}. -@end defun - -@defun check-coding-system coding-system -This function checks the validity of @var{coding-system}. -If that is valid, it returns @var{coding-system}. -Otherwise it signals an error with condition @code{coding-system-error}. -@end defun - -@defun coding-system-eol-type coding-system -This function returns the type of end-of-line (a.k.a.@: @dfn{eol}) -conversion used by @var{coding-system}. If @var{coding-system} -specifies a certain eol conversion, the return value is an integer 0, -1, or 2, standing for @code{unix}, @code{dos}, and @code{mac}, -respectively. If @var{coding-system} doesn't specify eol conversion -explicitly, the return value is a vector of coding systems, each one -with one of the possible eol conversion types, like this: - -@lisp -(coding-system-eol-type 'latin-1) - @result{} [latin-1-unix latin-1-dos latin-1-mac] -@end lisp - -@noindent -If this function returns a vector, Emacs will decide, as part of the -text encoding or decoding process, what eol conversion to use. For -decoding, the end-of-line format of the text is auto-detected, and the -eol conversion is set to match it (e.g., DOS-style CRLF format will -imply @code{dos} eol conversion). For encoding, the eol conversion is -taken from the appropriate default coding system (e.g., -@code{default-buffer-file-coding-system} for -@code{buffer-file-coding-system}), or from the default eol conversion -appropriate for the underlying platform. -@end defun - -@defun coding-system-change-eol-conversion coding-system eol-type -This function returns a coding system which is like @var{coding-system} -except for its eol conversion, which is specified by @code{eol-type}. -@var{eol-type} should be @code{unix}, @code{dos}, @code{mac}, or -@code{nil}. If it is @code{nil}, the returned coding system determines -the end-of-line conversion from the data. - -@var{eol-type} may also be 0, 1 or 2, standing for @code{unix}, -@code{dos} and @code{mac}, respectively. -@end defun - -@defun coding-system-change-text-conversion eol-coding text-coding -This function returns a coding system which uses the end-of-line -conversion of @var{eol-coding}, and the text conversion of -@var{text-coding}. If @var{text-coding} is @code{nil}, it returns -@code{undecided}, or one of its variants according to @var{eol-coding}. -@end defun - -@defun find-coding-systems-region from to -This function returns a list of coding systems that could be used to -encode a text between @var{from} and @var{to}. All coding systems in -the list can safely encode any multibyte characters in that portion of -the text. - -If the text contains no multibyte characters, the function returns the -list @code{(undecided)}. -@end defun - -@defun find-coding-systems-string string -This function returns a list of coding systems that could be used to -encode the text of @var{string}. All coding systems in the list can -safely encode any multibyte characters in @var{string}. If the text -contains no multibyte characters, this returns the list -@code{(undecided)}. -@end defun - -@defun find-coding-systems-for-charsets charsets -This function returns a list of coding systems that could be used to -encode all the character sets in the list @var{charsets}. -@end defun - -@defun detect-coding-region start end &optional highest -This function chooses a plausible coding system for decoding the text -from @var{start} to @var{end}. This text should be a byte sequence -(@pxref{Explicit Encoding}). - -Normally this function returns a list of coding systems that could -handle decoding the text that was scanned. They are listed in order of -decreasing priority. But if @var{highest} is non-@code{nil}, then the -return value is just one coding system, the one that is highest in -priority. - -If the region contains only @acronym{ASCII} characters except for such -ISO-2022 control characters ISO-2022 as @code{ESC}, the value is -@code{undecided} or @code{(undecided)}, or a variant specifying -end-of-line conversion, if that can be deduced from the text. -@end defun - -@defun detect-coding-string string &optional highest -This function is like @code{detect-coding-region} except that it -operates on the contents of @var{string} instead of bytes in the buffer. -@end defun - - @xref{Coding systems for a subprocess,, Process Information}, in -particular the description of the functions -@code{process-coding-system} and @code{set-process-coding-system}, for -how to examine or set the coding systems used for I/O to a subprocess. - -@node User-Chosen Coding Systems -@subsection User-Chosen Coding Systems - -@cindex select safe coding system -@defun select-safe-coding-system from to &optional default-coding-system accept-default-p file -This function selects a coding system for encoding specified text, -asking the user to choose if necessary. Normally the specified text -is the text in the current buffer between @var{from} and @var{to}. If -@var{from} is a string, the string specifies the text to encode, and -@var{to} is ignored. - -If @var{default-coding-system} is non-@code{nil}, that is the first -coding system to try; if that can handle the text, -@code{select-safe-coding-system} returns that coding system. It can -also be a list of coding systems; then the function tries each of them -one by one. After trying all of them, it next tries the current -buffer's value of @code{buffer-file-coding-system} (if it is not -@code{undecided}), then the value of -@code{default-buffer-file-coding-system} and finally the user's most -preferred coding system, which the user can set using the command -@code{prefer-coding-system} (@pxref{Recognize Coding,, Recognizing -Coding Systems, emacs, The GNU Emacs Manual}). - -If one of those coding systems can safely encode all the specified -text, @code{select-safe-coding-system} chooses it and returns it. -Otherwise, it asks the user to choose from a list of coding systems -which can encode all the text, and returns the user's choice. - -@var{default-coding-system} can also be a list whose first element is -t and whose other elements are coding systems. Then, if no coding -system in the list can handle the text, @code{select-safe-coding-system} -queries the user immediately, without trying any of the three -alternatives described above. - -The optional argument @var{accept-default-p}, if non-@code{nil}, -should be a function to determine whether a coding system selected -without user interaction is acceptable. @code{select-safe-coding-system} -calls this function with one argument, the base coding system of the -selected coding system. If @var{accept-default-p} returns @code{nil}, -@code{select-safe-coding-system} rejects the silently selected coding -system, and asks the user to select a coding system from a list of -possible candidates. - -@vindex select-safe-coding-system-accept-default-p -If the variable @code{select-safe-coding-system-accept-default-p} is -non-@code{nil}, its value overrides the value of -@var{accept-default-p}. - -As a final step, before returning the chosen coding system, -@code{select-safe-coding-system} checks whether that coding system is -consistent with what would be selected if the contents of the region -were read from a file. (If not, this could lead to data corruption in -a file subsequently re-visited and edited.) Normally, -@code{select-safe-coding-system} uses @code{buffer-file-name} as the -file for this purpose, but if @var{file} is non-@code{nil}, it uses -that file instead (this can be relevant for @code{write-region} and -similar functions). If it detects an apparent inconsistency, -@code{select-safe-coding-system} queries the user before selecting the -coding system. -@end defun - - Here are two functions you can use to let the user specify a coding -system, with completion. @xref{Completion}. - -@defun read-coding-system prompt &optional default -This function reads a coding system using the minibuffer, prompting with -string @var{prompt}, and returns the coding system name as a symbol. If -the user enters null input, @var{default} specifies which coding system -to return. It should be a symbol or a string. -@end defun - -@defun read-non-nil-coding-system prompt -This function reads a coding system using the minibuffer, prompting with -string @var{prompt}, and returns the coding system name as a symbol. If -the user tries to enter null input, it asks the user to try again. -@xref{Coding Systems}. -@end defun - -@node Default Coding Systems -@subsection Default Coding Systems - - This section describes variables that specify the default coding -system for certain files or when running certain subprograms, and the -function that I/O operations use to access them. - - The idea of these variables is that you set them once and for all to the -defaults you want, and then do not change them again. To specify a -particular coding system for a particular operation in a Lisp program, -don't change these variables; instead, override them using -@code{coding-system-for-read} and @code{coding-system-for-write} -(@pxref{Specifying Coding Systems}). - -@defvar auto-coding-regexp-alist -This variable is an alist of text patterns and corresponding coding -systems. Each element has the form @code{(@var{regexp} -. @var{coding-system})}; a file whose first few kilobytes match -@var{regexp} is decoded with @var{coding-system} when its contents are -read into a buffer. The settings in this alist take priority over -@code{coding:} tags in the files and the contents of -@code{file-coding-system-alist} (see below). The default value is set -so that Emacs automatically recognizes mail files in Babyl format and -reads them with no code conversions. -@end defvar - -@defvar file-coding-system-alist -This variable is an alist that specifies the coding systems to use for -reading and writing particular files. Each element has the form -@code{(@var{pattern} . @var{coding})}, where @var{pattern} is a regular -expression that matches certain file names. The element applies to file -names that match @var{pattern}. - -The @sc{cdr} of the element, @var{coding}, should be either a coding -system, a cons cell containing two coding systems, or a function name (a -symbol with a function definition). If @var{coding} is a coding system, -that coding system is used for both reading the file and writing it. If -@var{coding} is a cons cell containing two coding systems, its @sc{car} -specifies the coding system for decoding, and its @sc{cdr} specifies the -coding system for encoding. - -If @var{coding} is a function name, the function should take one -argument, a list of all arguments passed to -@code{find-operation-coding-system}. It must return a coding system -or a cons cell containing two coding systems. This value has the same -meaning as described above. -@end defvar - -@defvar process-coding-system-alist -This variable is an alist specifying which coding systems to use for a -subprocess, depending on which program is running in the subprocess. It -works like @code{file-coding-system-alist}, except that @var{pattern} is -matched against the program name used to start the subprocess. The coding -system or systems specified in this alist are used to initialize the -coding systems used for I/O to the subprocess, but you can specify -other coding systems later using @code{set-process-coding-system}. -@end defvar - - @strong{Warning:} Coding systems such as @code{undecided}, which -determine the coding system from the data, do not work entirely reliably -with asynchronous subprocess output. This is because Emacs handles -asynchronous subprocess output in batches, as it arrives. If the coding -system leaves the character code conversion unspecified, or leaves the -end-of-line conversion unspecified, Emacs must try to detect the proper -conversion from one batch at a time, and this does not always work. - - Therefore, with an asynchronous subprocess, if at all possible, use a -coding system which determines both the character code conversion and -the end of line conversion---that is, one like @code{latin-1-unix}, -rather than @code{undecided} or @code{latin-1}. - -@defvar network-coding-system-alist -This variable is an alist that specifies the coding system to use for -network streams. It works much like @code{file-coding-system-alist}, -with the difference that the @var{pattern} in an element may be either a -port number or a regular expression. If it is a regular expression, it -is matched against the network service name used to open the network -stream. -@end defvar - -@defvar default-process-coding-system -This variable specifies the coding systems to use for subprocess (and -network stream) input and output, when nothing else specifies what to -do. - -The value should be a cons cell of the form @code{(@var{input-coding} -. @var{output-coding})}. Here @var{input-coding} applies to input from -the subprocess, and @var{output-coding} applies to output to it. -@end defvar - -@defvar auto-coding-functions -This variable holds a list of functions that try to determine a -coding system for a file based on its undecoded contents. - -Each function in this list should be written to look at text in the -current buffer, but should not modify it in any way. The buffer will -contain undecoded text of parts of the file. Each function should -take one argument, @var{size}, which tells it how many characters to -look at, starting from point. If the function succeeds in determining -a coding system for the file, it should return that coding system. -Otherwise, it should return @code{nil}. - -If a file has a @samp{coding:} tag, that takes precedence, so these -functions won't be called. -@end defvar - -@defun find-operation-coding-system operation &rest arguments -This function returns the coding system to use (by default) for -performing @var{operation} with @var{arguments}. The value has this -form: - -@example -(@var{decoding-system} . @var{encoding-system}) -@end example - -The first element, @var{decoding-system}, is the coding system to use -for decoding (in case @var{operation} does decoding), and -@var{encoding-system} is the coding system for encoding (in case -@var{operation} does encoding). - -The argument @var{operation} is a symbol, one of @code{write-region}, -@code{start-process}, @code{call-process}, @code{call-process-region}, -@code{insert-file-contents}, or @code{open-network-stream}. These are -the names of the Emacs I/O primitives that can do character code and -eol conversion. - -The remaining arguments should be the same arguments that might be given -to the corresponding I/O primitive. Depending on the primitive, one -of those arguments is selected as the @dfn{target}. For example, if -@var{operation} does file I/O, whichever argument specifies the file -name is the target. For subprocess primitives, the process name is the -target. For @code{open-network-stream}, the target is the service name -or port number. - -Depending on @var{operation}, this function looks up the target in -@code{file-coding-system-alist}, @code{process-coding-system-alist}, -or @code{network-coding-system-alist}. If the target is found in the -alist, @code{find-operation-coding-system} returns its association in -the alist; otherwise it returns @code{nil}. - -If @var{operation} is @code{insert-file-contents}, the argument -corresponding to the target may be a cons cell of the form -@code{(@var{filename} . @var{buffer})}). In that case, @var{filename} -is a file name to look up in @code{file-coding-system-alist}, and -@var{buffer} is a buffer that contains the file's contents (not yet -decoded). If @code{file-coding-system-alist} specifies a function to -call for this file, and that function needs to examine the file's -contents (as it usually does), it should examine the contents of -@var{buffer} instead of reading the file. -@end defun - -@node Specifying Coding Systems -@subsection Specifying a Coding System for One Operation - - You can specify the coding system for a specific operation by binding -the variables @code{coding-system-for-read} and/or -@code{coding-system-for-write}. - -@defvar coding-system-for-read -If this variable is non-@code{nil}, it specifies the coding system to -use for reading a file, or for input from a synchronous subprocess. - -It also applies to any asynchronous subprocess or network stream, but in -a different way: the value of @code{coding-system-for-read} when you -start the subprocess or open the network stream specifies the input -decoding method for that subprocess or network stream. It remains in -use for that subprocess or network stream unless and until overridden. - -The right way to use this variable is to bind it with @code{let} for a -specific I/O operation. Its global value is normally @code{nil}, and -you should not globally set it to any other value. Here is an example -of the right way to use the variable: - -@example -;; @r{Read the file with no character code conversion.} -;; @r{Assume @acronym{crlf} represents end-of-line.} -(let ((coding-system-for-read 'emacs-mule-dos)) - (insert-file-contents filename)) -@end example - -When its value is non-@code{nil}, this variable takes precedence over -all other methods of specifying a coding system to use for input, -including @code{file-coding-system-alist}, -@code{process-coding-system-alist} and -@code{network-coding-system-alist}. -@end defvar - -@defvar coding-system-for-write -This works much like @code{coding-system-for-read}, except that it -applies to output rather than input. It affects writing to files, -as well as sending output to subprocesses and net connections. - -When a single operation does both input and output, as do -@code{call-process-region} and @code{start-process}, both -@code{coding-system-for-read} and @code{coding-system-for-write} -affect it. -@end defvar - -@defvar inhibit-eol-conversion -When this variable is non-@code{nil}, no end-of-line conversion is done, -no matter which coding system is specified. This applies to all the -Emacs I/O and subprocess primitives, and to the explicit encoding and -decoding functions (@pxref{Explicit Encoding}). -@end defvar - -@node Explicit Encoding -@subsection Explicit Encoding and Decoding -@cindex encoding in coding systems -@cindex decoding in coding systems - - All the operations that transfer text in and out of Emacs have the -ability to use a coding system to encode or decode the text. -You can also explicitly encode and decode text using the functions -in this section. - - The result of encoding, and the input to decoding, are not ordinary -text. They logically consist of a series of byte values; that is, a -series of characters whose codes are in the range 0 through 255. In a -multibyte buffer or string, character codes 128 through 159 are -represented by multibyte sequences, but this is invisible to Lisp -programs. - - The usual way to read a file into a buffer as a sequence of bytes, so -you can decode the contents explicitly, is with -@code{insert-file-contents-literally} (@pxref{Reading from Files}); -alternatively, specify a non-@code{nil} @var{rawfile} argument when -visiting a file with @code{find-file-noselect}. These methods result in -a unibyte buffer. - - The usual way to use the byte sequence that results from explicitly -encoding text is to copy it to a file or process---for example, to write -it with @code{write-region} (@pxref{Writing to Files}), and suppress -encoding by binding @code{coding-system-for-write} to -@code{no-conversion}. - - Here are the functions to perform explicit encoding or decoding. The -encoding functions produce sequences of bytes; the decoding functions -are meant to operate on sequences of bytes. All of these functions -discard text properties. - -@deffn Command encode-coding-region start end coding-system -This command encodes the text from @var{start} to @var{end} according -to coding system @var{coding-system}. The encoded text replaces the -original text in the buffer. The result of encoding is logically a -sequence of bytes, but the buffer remains multibyte if it was multibyte -before. - -This command returns the length of the encoded text. -@end deffn - -@defun encode-coding-string string coding-system &optional nocopy -This function encodes the text in @var{string} according to coding -system @var{coding-system}. It returns a new string containing the -encoded text, except when @var{nocopy} is non-@code{nil}, in which -case the function may return @var{string} itself if the encoding -operation is trivial. The result of encoding is a unibyte string. -@end defun - -@deffn Command decode-coding-region start end coding-system -This command decodes the text from @var{start} to @var{end} according -to coding system @var{coding-system}. The decoded text replaces the -original text in the buffer. To make explicit decoding useful, the text -before decoding ought to be a sequence of byte values, but both -multibyte and unibyte buffers are acceptable. - -This command returns the length of the decoded text. -@end deffn - -@defun decode-coding-string string coding-system &optional nocopy -This function decodes the text in @var{string} according to coding -system @var{coding-system}. It returns a new string containing the -decoded text, except when @var{nocopy} is non-@code{nil}, in which -case the function may return @var{string} itself if the decoding -operation is trivial. To make explicit decoding useful, the contents -of @var{string} ought to be a sequence of byte values, but a multibyte -string is acceptable. -@end defun - -@defun decode-coding-inserted-region from to filename &optional visit beg end replace -This function decodes the text from @var{from} to @var{to} as if -it were being read from file @var{filename} using @code{insert-file-contents} -using the rest of the arguments provided. - -The normal way to use this function is after reading text from a file -without decoding, if you decide you would rather have decoded it. -Instead of deleting the text and reading it again, this time with -decoding, you can call this function. -@end defun - -@node Terminal I/O Encoding -@subsection Terminal I/O Encoding - - Emacs can decode keyboard input using a coding system, and encode -terminal output. This is useful for terminals that transmit or display -text using a particular encoding such as Latin-1. Emacs does not set -@code{last-coding-system-used} for encoding or decoding for the -terminal. - -@defun keyboard-coding-system -This function returns the coding system that is in use for decoding -keyboard input---or @code{nil} if no coding system is to be used. -@end defun - -@deffn Command set-keyboard-coding-system coding-system -This command specifies @var{coding-system} as the coding system to -use for decoding keyboard input. If @var{coding-system} is @code{nil}, -that means do not decode keyboard input. -@end deffn - -@defun terminal-coding-system -This function returns the coding system that is in use for encoding -terminal output---or @code{nil} for no encoding. -@end defun - -@deffn Command set-terminal-coding-system coding-system -This command specifies @var{coding-system} as the coding system to use -for encoding terminal output. If @var{coding-system} is @code{nil}, -that means do not encode terminal output. -@end deffn - -@node MS-DOS File Types -@subsection MS-DOS File Types -@cindex DOS file types -@cindex MS-DOS file types -@cindex Windows file types -@cindex file types on MS-DOS and Windows -@cindex text files and binary files -@cindex binary files and text files - - On MS-DOS and Microsoft Windows, Emacs guesses the appropriate -end-of-line conversion for a file by looking at the file's name. This -feature classifies files as @dfn{text files} and @dfn{binary files}. By -``binary file'' we mean a file of literal byte values that are not -necessarily meant to be characters; Emacs does no end-of-line conversion -and no character code conversion for them. On the other hand, the bytes -in a text file are intended to represent characters; when you create a -new file whose name implies that it is a text file, Emacs uses DOS -end-of-line conversion. - -@defvar buffer-file-type -This variable, automatically buffer-local in each buffer, records the -file type of the buffer's visited file. When a buffer does not specify -a coding system with @code{buffer-file-coding-system}, this variable is -used to determine which coding system to use when writing the contents -of the buffer. It should be @code{nil} for text, @code{t} for binary. -If it is @code{t}, the coding system is @code{no-conversion}. -Otherwise, @code{undecided-dos} is used. - -Normally this variable is set by visiting a file; it is set to -@code{nil} if the file was visited without any actual conversion. -@end defvar - -@defopt file-name-buffer-file-type-alist -This variable holds an alist for recognizing text and binary files. -Each element has the form (@var{regexp} . @var{type}), where -@var{regexp} is matched against the file name, and @var{type} may be -@code{nil} for text, @code{t} for binary, or a function to call to -compute which. If it is a function, then it is called with a single -argument (the file name) and should return @code{t} or @code{nil}. - -When running on MS-DOS or MS-Windows, Emacs checks this alist to decide -which coding system to use when reading a file. For a text file, -@code{undecided-dos} is used. For a binary file, @code{no-conversion} -is used. - -If no element in this alist matches a given file name, then -@code{default-buffer-file-type} says how to treat the file. -@end defopt - -@defopt default-buffer-file-type -This variable says how to handle files for which -@code{file-name-buffer-file-type-alist} says nothing about the type. - -If this variable is non-@code{nil}, then these files are treated as -binary: the coding system @code{no-conversion} is used. Otherwise, -nothing special is done for them---the coding system is deduced solely -from the file contents, in the usual Emacs fashion. -@end defopt - -@node Input Methods -@section Input Methods -@cindex input methods - - @dfn{Input methods} provide convenient ways of entering non-@acronym{ASCII} -characters from the keyboard. Unlike coding systems, which translate -non-@acronym{ASCII} characters to and from encodings meant to be read by -programs, input methods provide human-friendly commands. (@xref{Input -Methods,,, emacs, The GNU Emacs Manual}, for information on how users -use input methods to enter text.) How to define input methods is not -yet documented in this manual, but here we describe how to use them. - - Each input method has a name, which is currently a string; -in the future, symbols may also be usable as input method names. - -@defvar current-input-method -This variable holds the name of the input method now active in the -current buffer. (It automatically becomes local in each buffer when set -in any fashion.) It is @code{nil} if no input method is active in the -buffer now. -@end defvar - -@defopt default-input-method -This variable holds the default input method for commands that choose an -input method. Unlike @code{current-input-method}, this variable is -normally global. -@end defopt - -@deffn Command set-input-method input-method -This command activates input method @var{input-method} for the current -buffer. It also sets @code{default-input-method} to @var{input-method}. -If @var{input-method} is @code{nil}, this command deactivates any input -method for the current buffer. -@end deffn - -@defun read-input-method-name prompt &optional default inhibit-null -This function reads an input method name with the minibuffer, prompting -with @var{prompt}. If @var{default} is non-@code{nil}, that is returned -by default, if the user enters empty input. However, if -@var{inhibit-null} is non-@code{nil}, empty input signals an error. - -The returned value is a string. -@end defun - -@defvar input-method-alist -This variable defines all the supported input methods. -Each element defines one input method, and should have the form: - -@example -(@var{input-method} @var{language-env} @var{activate-func} - @var{title} @var{description} @var{args}...) -@end example - -Here @var{input-method} is the input method name, a string; -@var{language-env} is another string, the name of the language -environment this input method is recommended for. (That serves only for -documentation purposes.) - -@var{activate-func} is a function to call to activate this method. The -@var{args}, if any, are passed as arguments to @var{activate-func}. All -told, the arguments to @var{activate-func} are @var{input-method} and -the @var{args}. - -@var{title} is a string to display in the mode line while this method is -active. @var{description} is a string describing this method and what -it is good for. -@end defvar - - The fundamental interface to input methods is through the -variable @code{input-method-function}. @xref{Reading One Event}, -and @ref{Invoking the Input Method}. - -@node Locales -@section Locales -@cindex locale - - POSIX defines a concept of ``locales'' which control which language -to use in language-related features. These Emacs variables control -how Emacs interacts with these features. - -@defvar locale-coding-system -@cindex keyboard input decoding on X -This variable specifies the coding system to use for decoding system -error messages and---on X Window system only---keyboard input, for -encoding the format argument to @code{format-time-string}, and for -decoding the return value of @code{format-time-string}. -@end defvar - -@defvar system-messages-locale -This variable specifies the locale to use for generating system error -messages. Changing the locale can cause messages to come out in a -different language or in a different orthography. If the variable is -@code{nil}, the locale is specified by environment variables in the -usual POSIX fashion. -@end defvar - -@defvar system-time-locale -This variable specifies the locale to use for formatting time values. -Changing the locale can cause messages to appear according to the -conventions of a different language. If the variable is @code{nil}, the -locale is specified by environment variables in the usual POSIX fashion. -@end defvar - -@defun locale-info item -This function returns locale data @var{item} for the current POSIX -locale, if available. @var{item} should be one of these symbols: - -@table @code -@item codeset -Return the character set as a string (locale item @code{CODESET}). - -@item days -Return a 7-element vector of day names (locale items -@code{DAY_1} through @code{DAY_7}); - -@item months -Return a 12-element vector of month names (locale items @code{MON_1} -through @code{MON_12}). - -@item paper -Return a list @code{(@var{width} @var{height})} for the default paper -size measured in millimeters (locale items @code{PAPER_WIDTH} and -@code{PAPER_HEIGHT}). -@end table - -If the system can't provide the requested information, or if -@var{item} is not one of those symbols, the value is @code{nil}. All -strings in the return value are decoded using -@code{locale-coding-system}. @xref{Locales,,, libc, The GNU Libc Manual}, -for more information about locales and locale items. -@end defun - -@ignore - arch-tag: be705bf8-941b-4c35-84fc-ad7d20ddb7cb -@end ignore |