class Encoding - Documentation for Ruby 4.0
Description: class Encoding: An \Encoding instance represents a character encoding usable in Ruby. It is defined as a constant under the \Encoding namespace.
Keywords: ruby,class,Encoding

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# class Encoding

An Encoding instance represents a character encoding usable in Ruby. It is defined as a constant under the Encoding namespace. It has a name and, optionally, aliases:

    Encoding::US_ASCII.name  # => "US-ASCII"
    Encoding::US_ASCII.names # => ["US-ASCII", "ASCII", "ANSI_X3.4-1968", "646"]

A Ruby method that accepts an encoding as an argument will accept:

- An Encoding object.

- The name of an encoding.

- An alias for an encoding name.

These are equivalent:

    'foo'.encode(Encoding::US_ASCII) # Encoding object.
    'foo'.encode('US-ASCII')         # Encoding name.
    'foo'.encode('ASCII')            # Encoding alias.

For a full discussion of encodings and their uses, see the Encodings document.

Encoding::ASCII_8BIT is a special-purpose encoding that is usually used for a string of bytes, not a string of characters. But as the name indicates, its characters in the ASCII range are considered as ASCII characters. This is useful when you use other ASCII-compatible encodings.

### Constants

UNICODE_VERSION

  The supported Unicode version.

### Attributes

name [R]

The name of the encoding.

    Encoding::UTF_8.name      #=> "UTF-8"

to_s [R]

The name of the encoding.

    Encoding::UTF_8.name      #=> "UTF-8"

### Public Class Methods

aliases -> {"alias1" => "orig1", "alias2" → "orig2", ...}
Source

    static VALUE
    rb_enc_aliases(VALUE klass)
    {
        VALUE aliases[2];
        aliases[0] = rb_hash_new();
        aliases[1] = rb_ary_new();

        GLOBAL_ENC_TABLE_LOCKING(enc_table) {
            st_foreach(enc_table->names, rb_enc_aliases_enc_i, (st_data_t)aliases);
        }

        return aliases[0];
    }

Returns the hash of available encoding alias and original encoding name.

    Encoding.aliases
    #=> {"BINARY"=>"ASCII-8BIT", "ASCII"=>"US-ASCII", "ANSI_X3.4-1968"=>"US-ASCII",
          "SJIS"=>"Windows-31J", "eucJP"=>"EUC-JP", "CP932"=>"Windows-31J"}

compatible?(obj1, obj2) → enc or nil
Source

    static VALUE
    enc_compatible_p(VALUE klass, VALUE str1, VALUE str2)
    {
        rb_encoding *enc;

        if (!enc_capable(str1)) return Qnil;
        if (!enc_capable(str2)) return Qnil;
        enc = rb_enc_compatible(str1, str2);
        if (!enc) return Qnil;
        return rb_enc_from_encoding(enc);
    }

Checks the compatibility of two objects.

If the objects are both strings they are compatible when they are concatenatable. The encoding of the concatenated string will be returned if they are compatible, nil if they are not.

    Encoding.compatible?("\xa1".force_encoding("iso-8859-1"), "b")
    #=> #<Encoding:ISO-8859-1>

    Encoding.compatible?(
      "\xa1".force_encoding("iso-8859-1"),
      "\xa1\xa1".force_encoding("euc-jp"))
    #=> nil

If the objects are non-strings their encodings are compatible when they have an encoding and:

- Either encoding is US-ASCII compatible

- One of the encodings is a 7-bit encoding

default_external → enc
Source

    static VALUE
    get_default_external(VALUE klass)
    {
        return rb_enc_default_external();
    }

Returns default external encoding.

The default external encoding is used by default for strings created from the following locations:

- CSV

- `File` data read from disk

- SDBM

- `StringIO`

- `Zlib::GzipReader`

- `Zlib::GzipWriter`

- `String#inspect`

- `Regexp#inspect`

While strings created from these locations will have this encoding, the encoding may not be valid. Be sure to check `String#valid_encoding?`.

`File` data written to disk will be transcoded to the default external encoding when written, if `default_internal` is not nil.

The default external encoding is initialized by the -E option. If -E isn’t set, it is initialized to UTF-8 on Windows and the locale on other operating systems.

default_external = enc
Source

    static VALUE
    set_default_external(VALUE klass, VALUE encoding)
    {
        rb_warning("setting Encoding.default_external");
        rb_enc_set_default_external(encoding);
        return encoding;
    }

Sets default external encoding. You should not set `Encoding::default_external` in ruby code as strings created before changing the value may have a different encoding from strings created after the value was changed., instead you should use `ruby -E` to invoke ruby with the correct default_external.

See `Encoding::default_external` for information on how the default external encoding is used.

default_internal → enc
Source

    static VALUE
    get_default_internal(VALUE klass)
    {
        return rb_enc_default_internal();
    }

Returns default internal encoding. Strings will be transcoded to the default internal encoding in the following places if the default internal encoding is not nil:

- CSV

- `Etc.sysconfdir` and `Etc.systmpdir`

- `File` data read from disk

- `File` names from `Dir`

- `Integer#chr`

- `String#inspect` and `Regexp#inspect`

- Strings returned from Readline

- Strings returned from SDBM

- `Time#zone`

- Values from `ENV`

- Values in ARGV including $PROGRAM_NAME

Additionally `String#encode` and `String#encode!` use the default internal encoding if no encoding is given.

The script encoding (__ENCODING__), not `default_internal`, is used as the encoding of created strings.

`Encoding::default_internal` is initialized with -E option or nil otherwise.

default_internal = enc or nil
Source

    static VALUE
    set_default_internal(VALUE klass, VALUE encoding)
    {
        rb_warning("setting Encoding.default_internal");
        rb_enc_set_default_internal(encoding);
        return encoding;
    }

Sets default internal encoding or removes default internal encoding when passed nil. You should not set `Encoding::default_internal` in ruby code as strings created before changing the value may have a different encoding from strings created after the change. Instead you should use `ruby -E` to invoke ruby with the correct default_internal.

See `Encoding::default_internal` for information on how the default internal encoding is used.

find(string) → enc
Source

    static VALUE
    enc_find(VALUE klass, VALUE enc)
    {
        int idx;
        if (is_obj_encoding(enc))
            return enc;
        idx = str_to_encindex(enc);
        if (idx == UNSPECIFIED_ENCODING) return Qnil;
        return rb_enc_from_encoding_index(idx);
    }

Search the encoding with specified name. name should be a string.

    Encoding.find("US-ASCII")  #=> #<Encoding:US-ASCII>

Names which this method accept are encoding names and aliases including following special aliases

“external”

  default external encoding

“internal”

  default internal encoding

“locale”

  locale encoding

“filesystem”

  filesystem encoding

An `ArgumentError` is raised when no encoding with name. Only `Encoding.find("internal")` however returns nil when no encoding named “internal”, in other words, when Ruby has no default internal encoding.

list → [enc1, enc2, ...]
Source

    static VALUE
    enc_list(VALUE klass)
    {
        VALUE list = RUBY_ATOMIC_VALUE_LOAD(rb_encoding_list);
        return rb_ary_dup(list);
    }

Returns the list of loaded encodings.

    Encoding.list
    #=> [#<Encoding:ASCII-8BIT>, #<Encoding:UTF-8>,
          #<Encoding:ISO-2022-JP (dummy)>]

    Encoding.find("US-ASCII")
    #=> #<Encoding:US-ASCII>

    Encoding.list
    #=> [#<Encoding:ASCII-8BIT>, #<Encoding:UTF-8>,
          #<Encoding:US-ASCII>, #<Encoding:ISO-2022-JP (dummy)>]

locale_charmap → string
Source

    VALUE
    rb_locale_charmap(VALUE klass)
    {
    #if NO_LOCALE_CHARMAP
        return rb_usascii_str_new_cstr("US-ASCII");
    #else
        return locale_charmap(rb_usascii_str_new_cstr);
    #endif
    }

Returns the locale charmap name. It returns nil if no appropriate information.

    Debian GNU/Linux
      LANG=C
        Encoding.locale_charmap  #=> "ANSI_X3.4-1968"
      LANG=ja_JP.EUC-JP
        Encoding.locale_charmap  #=> "EUC-JP"

    SunOS 5
      LANG=C
        Encoding.locale_charmap  #=> "646"
      LANG=ja
        Encoding.locale_charmap  #=> "eucJP"

The result is highly platform dependent. So `Encoding.find(Encoding.locale_charmap)` may cause an error. If you need some encoding object even for unknown locale, `Encoding.find`(“locale”) can be used.

name_list → ["enc1", "enc2", ...]
Source

    static VALUE
    rb_enc_name_list(VALUE klass)
    {
        VALUE ary;
        GLOBAL_ENC_TABLE_LOCKING(enc_table) {
            ary = rb_ary_new2(enc_table->names->num_entries);
            st_foreach(enc_table->names, rb_enc_name_list_i, (st_data_t)ary);
        }
        return ary;
    }

Returns the list of available encoding names.

    Encoding.name_list
    #=> ["US-ASCII", "ASCII-8BIT", "UTF-8",
          "ISO-8859-1", "Shift_JIS", "EUC-JP",
          "Windows-31J",
          "BINARY", "CP932", "eucJP"]

### Public Instance Methods

ascii_compatible? → true or false
Source

    static VALUE
    enc_ascii_compatible_p(VALUE enc)
    {
        return RBOOL(rb_enc_asciicompat(must_encoding(enc)));
    }

Returns whether ASCII-compatible or not.

    Encoding::UTF_8.ascii_compatible?     #=> true
    Encoding::UTF_16BE.ascii_compatible?  #=> false

dummy? → true or false
Source

    static VALUE
    enc_dummy_p(VALUE enc)
    {
        return RBOOL(ENC_DUMMY_P(must_encoding(enc)));
    }

Returns true for dummy encodings. A dummy encoding is an encoding for which character handling is not properly implemented. It is used for stateful encodings.

    Encoding::ISO_2022_JP.dummy?       #=> true
    Encoding::UTF_8.dummy?             #=> false

inspect → string
Source

    static VALUE
    enc_inspect(VALUE self)
    {
        rb_encoding *enc;

        if (!is_data_encoding(self)) {
            not_encoding(self);
        }
        if (!(enc = RTYPEDDATA_GET_DATA(self)) || rb_enc_from_index(rb_enc_to_index(enc)) != enc) {
            rb_raise(rb_eTypeError, "broken Encoding");
        }

        return rb_enc_sprintf(rb_usascii_encoding(),
                              "#<%"PRIsVALUE":%s%s%s>", rb_obj_class(self),
                              rb_enc_inspect_name(enc),
                              (ENC_DUMMY_P(enc) ? " (dummy)" : ""),
                              rb_enc_autoload_p(enc) ? " (autoload)" : "");
    }

Returns a string which represents the encoding for programmers.

    Encoding::UTF_8.inspect       #=> "#<Encoding:UTF-8>"
    Encoding::ISO_2022_JP.inspect #=> "#<Encoding:ISO-2022-JP (dummy)>"

names → array
Source

    static VALUE
    enc_names(VALUE self)
    {
        VALUE args[2];

        args[0] = (VALUE)rb_to_encoding_index(self);
        args[1] = rb_ary_new2(0);

        GLOBAL_ENC_TABLE_LOCKING(enc_table) {
            st_foreach(enc_table->names, enc_names_i, (st_data_t)args);
        }
        return args[1];
    }

Returns the list of name and aliases of the encoding.

    Encoding::WINDOWS_31J.names  #=> ["Windows-31J", "CP932", "csWindows31J", "SJIS", "PCK"]