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[DOC] Main doc for encodings moved from encoding.c to doc/encodings.rdoc (#5748)
Main doc for encodings moved from encoding.c to doc/encodings.rdoc
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Burdette Lamar
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@ -1,4 +1,4 @@
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== \Encoding
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== Encodings
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=== The Basics
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@ -12,7 +12,7 @@ with the same encoding as +string+:
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s.encoding # => #<Encoding:UTF-8>
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Literal strings like <tt>""</tt> or here-documents always use
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Encoding@Script+encoding, unlike String.new.
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{script encoding}[rdoc-ref:encodings.rdoc@Script+Encoding], unlike String.new.
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With keyword +encoding+, returns a copy of +str+
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with the specified encoding:
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210
encoding.c
210
encoding.c
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@ -1936,203 +1936,33 @@ rb_enc_aliases(VALUE klass)
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}
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/*
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* An Encoding instance represents a character encoding usable in Ruby. It is
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* defined as a constant under the Encoding namespace. It has a name and
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* optionally, aliases:
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* An \Encoding instance represents a character encoding usable in Ruby.
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* It is defined as a constant under the \Encoding namespace.
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* It has a name and, optionally, aliases:
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*
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* Encoding::ISO_8859_1.name
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* #=> "ISO-8859-1"
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* Encoding::US_ASCII.name # => "US-ASCII"
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* Encoding::US_ASCII.names # => ["US-ASCII", "ASCII", "ANSI_X3.4-1968", "646"]
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*
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* Encoding::ISO_8859_1.names
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* #=> ["ISO-8859-1", "ISO8859-1"]
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* A Ruby method that accepts an encoding as an argument will accept:
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*
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* Ruby methods dealing with encodings return or accept Encoding instances as
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* arguments (when a method accepts an Encoding instance as an argument, it
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* can be passed an Encoding name or alias instead).
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* - An \Encoding object.
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* - The name of an encoding.
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* - An alias for an encoding name.
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*
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* "some string".encoding
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* #=> #<Encoding:UTF-8>
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* These are equivalent:
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*
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* string = "some string".encode(Encoding::ISO_8859_1)
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* #=> "some string"
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* string.encoding
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* #=> #<Encoding:ISO-8859-1>
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* 'foo'.encode(Encoding::US_ASCII) # Encoding object.
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* 'foo'.encode('US-ASCII') # Encoding name.
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* 'foo'.encode('ASCII') # Encoding alias.
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*
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* "some string".encode "ISO-8859-1"
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* #=> "some string"
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* For a full discussion of encodings and their uses,
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* see {the Encodings document}[rdoc-ref:encodings.rdoc].
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*
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* Encoding::ASCII_8BIT is a special encoding that is usually used for
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* a byte string, not a character string. But as the name insists, its
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* characters in the range of ASCII are considered as ASCII
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* characters. This is useful when you use ASCII-8BIT characters with
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* other ASCII compatible characters.
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*
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* == Changing an encoding
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*
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* The associated Encoding of a String can be changed in two different ways.
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*
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* First, it is possible to set the Encoding of a string to a new Encoding
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* without changing the internal byte representation of the string, with
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* String#force_encoding. This is how you can tell Ruby the correct encoding
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* of a string.
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*
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* string
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* #=> "R\xC3\xA9sum\xC3\xA9"
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* string.encoding
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* #=> #<Encoding:ISO-8859-1>
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* string.force_encoding(Encoding::UTF_8)
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* #=> "R\u00E9sum\u00E9"
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*
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* Second, it is possible to transcode a string, i.e. translate its internal
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* byte representation to another encoding. Its associated encoding is also
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* set to the other encoding. See String#encode for the various forms of
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* transcoding, and the Encoding::Converter class for additional control over
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* the transcoding process.
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*
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* string
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* #=> "R\u00E9sum\u00E9"
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* string.encoding
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* #=> #<Encoding:UTF-8>
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* string = string.encode!(Encoding::ISO_8859_1)
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* #=> "R\xE9sum\xE9"
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* string.encoding
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* #=> #<Encoding::ISO-8859-1>
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*
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* == Script encoding
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*
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* All Ruby script code has an associated Encoding which any String literal
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* created in the source code will be associated to.
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*
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* The default script encoding is Encoding::UTF_8 after v2.0, but it
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* can be changed by a magic comment on the first line of the source
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* code file (or second line, if there is a shebang line on the
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* first). The comment must contain the word <code>coding</code> or
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* <code>encoding</code>, followed by a colon, space and the Encoding
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* name or alias:
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*
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* # encoding: UTF-8
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*
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* "some string".encoding
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* #=> #<Encoding:UTF-8>
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*
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* The <code>__ENCODING__</code> keyword returns the script encoding of the file
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* which the keyword is written:
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*
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* # encoding: ISO-8859-1
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*
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* __ENCODING__
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* #=> #<Encoding:ISO-8859-1>
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*
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* <code>ruby -K</code> will change the default locale encoding, but this is
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* not recommended. Ruby source files should declare its script encoding by a
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* magic comment even when they only depend on US-ASCII strings or regular
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* expressions.
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*
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* == Locale encoding
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*
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* The default encoding of the environment. Usually derived from locale.
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*
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* see Encoding.locale_charmap, Encoding.find('locale')
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*
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* == Filesystem encoding
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*
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* The default encoding of strings from the filesystem of the environment.
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* This is used for strings of file names or paths.
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*
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* see Encoding.find('filesystem')
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*
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* == External encoding
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*
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* Each IO object has an external encoding which indicates the encoding that
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* Ruby will use to read its data. By default Ruby sets the external encoding
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* of an IO object to the default external encoding. The default external
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* encoding is set by locale encoding or the interpreter <code>-E</code> option.
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* Encoding.default_external returns the current value of the external
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* encoding.
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*
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* ENV["LANG"]
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* #=> "UTF-8"
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* Encoding.default_external
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* #=> #<Encoding:UTF-8>
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*
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* $ ruby -E ISO-8859-1 -e "p Encoding.default_external"
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* #<Encoding:ISO-8859-1>
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*
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* $ LANG=C ruby -e 'p Encoding.default_external'
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* #<Encoding:US-ASCII>
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*
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* The default external encoding may also be set through
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* Encoding.default_external=, but you should not do this as strings created
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* before and after the change will have inconsistent encodings. Instead use
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* <code>ruby -E</code> to invoke ruby with the correct external encoding.
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*
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* When you know that the actual encoding of the data of an IO object is not
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* the default external encoding, you can reset its external encoding with
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* IO#set_encoding or set it at IO object creation (see IO.new options).
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*
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* == Internal encoding
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*
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* To process the data of an IO object which has an encoding different
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* from its external encoding, you can set its internal encoding. Ruby will use
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* this internal encoding to transcode the data when it is read from the IO
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* object.
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*
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* Conversely, when data is written to the IO object it is transcoded from the
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* internal encoding to the external encoding of the IO object.
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*
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* The internal encoding of an IO object can be set with
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* IO#set_encoding or at IO object creation (see IO.new options).
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*
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* The internal encoding is optional and when not set, the Ruby default
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* internal encoding is used. If not explicitly set this default internal
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* encoding is +nil+ meaning that by default, no transcoding occurs.
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*
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* The default internal encoding can be set with the interpreter option
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* <code>-E</code>. Encoding.default_internal returns the current internal
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* encoding.
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*
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* $ ruby -e 'p Encoding.default_internal'
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* nil
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*
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* $ ruby -E ISO-8859-1:UTF-8 -e "p [Encoding.default_external, \
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* Encoding.default_internal]"
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* [#<Encoding:ISO-8859-1>, #<Encoding:UTF-8>]
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*
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* The default internal encoding may also be set through
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* Encoding.default_internal=, but you should not do this as strings created
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* before and after the change will have inconsistent encodings. Instead use
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* <code>ruby -E</code> to invoke ruby with the correct internal encoding.
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*
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* == IO encoding example
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*
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* In the following example a UTF-8 encoded string "R\u00E9sum\u00E9" is transcoded for
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* output to ISO-8859-1 encoding, then read back in and transcoded to UTF-8:
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*
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* string = "R\u00E9sum\u00E9"
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*
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* open("transcoded.txt", "w:ISO-8859-1") do |io|
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* io.write(string)
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* end
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*
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* puts "raw text:"
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* p File.binread("transcoded.txt")
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* puts
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*
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* open("transcoded.txt", "r:ISO-8859-1:UTF-8") do |io|
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* puts "transcoded text:"
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* p io.read
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* end
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*
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* While writing the file, the internal encoding is not specified as it is
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* only necessary for reading. While reading the file both the internal and
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* external encoding must be specified to obtain the correct result.
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*
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* $ ruby t.rb
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* raw text:
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* "R\xE9sum\xE9"
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*
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* transcoded text:
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* "R\u00E9sum\u00E9"
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* Encoding::ASCII_8BIT is a special-purpose encoding that is usually used for
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* a string of bytes, not a string of characters.
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* But as the name indicates, its characters in the ASCII range
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* are considered as ASCII characters.
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* This is useful when you use other ASCII-compatible encodings.
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*
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*/
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