Class: Encoding

Inherits:
Object show all
Defined in:
encoding.c

Overview

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::ISO_8859_1.name
#=> #<Encoding:ISO-8859-1>

Encoding::ISO_8859_1.names
#=> ["ISO-8859-1", "ISO8859-1"]

Ruby methods dealing with encodings return or accept Encoding instances as arguments (when a method accepts an Encoding instance as an argument, it can be passed an Encoding name or alias instead).

"some string".encoding
#=> #<Encoding:UTF-8>

string = "some string".encode(Encoding::ISO_8859_1)
#=> "some string"
string.encoding
#=> #<Encoding:ISO-8859-1>

"some string".encode "ISO-8859-1"
#=> "some string"

Encoding::ASCII_8BIT is a special encoding that is usually used for a byte string, not a character string. But as the name insists, its characters in the range of ASCII are considered as ASCII characters. This is useful when you use ASCII-8BIT characters with other ASCII compatible characters.

Changing an encoding

The associated Encoding of a String can be changed in two different ways.

First, it is possible to set the Encoding of a string to a new Encoding without changing the internal byte representation of the string, with String#force_encoding. This is how you can tell Ruby the correct encoding of a string.

string
#=> "R\xC3\xA9sum\xC3\xA9"
string.encoding
#=> #<Encoding:ISO-8859-1>
string.force_encoding(Encoding::UTF-8)
#=> "R\u00E9sum\u00E9"

Second, it is possible to transcode a string, i.e. translate its internal byte representation to another encoding. Its associated encoding is also set to the other encoding. See String#encode for the various forms of transcoding, and the Encoding::Converter class for additional control over the transcoding process.

string
#=> "R\u00E9sum\u00E9"
string.encoding
#=> #<Encoding:UTF-8>
string = string.encode!(Encoding::ISO_8859_1)
#=> "R\xE9sum\xE9"
string.encoding
#=> #<Encoding::ISO-8859-1>

Script encoding

All Ruby script code has an associated Encoding which any String literal created in the source code will be associated to.

The default script encoding is Encoding::US-ASCII, but it can be changed by a magic comment on the first line of the source code file (or second line, if there is a shebang line on the first). The comment must contain the word coding or encoding, followed by a colon, space and the Encoding name or alias:

# encoding: UTF-8

"some string".encoding
#=> #<Encoding:UTF-8>

The __ENCODING__ keyword returns the script encoding of the file which the keyword is written:

# encoding: ISO-8859-1

__ENCODING__
#=> #<Encoding:ISO-8859-1>

ruby -K will change the default locale encoding, but this is not recommended. Ruby source files should declare its script encoding by a magic comment even when they only depend on US-ASCII strings or regular expressions.

Locale encoding

The default encoding of the environment. Usually derived from locale.

see Encoding.locale_charmap, Encoding.find('locale')

Filesystem encoding

The default encoding of strings from the filesystem of the environment. This is used for strings of file names or paths.

see Encoding.find('filesystem')

External encoding

Each IO object has an external encoding which indicates the encoding that Ruby will use to read its data. By default Ruby sets the external encoding of an IO object to the default external encoding. The default external encoding is set by locale encoding or the interpreter -E option. Encoding.default_external returns the current value of the external encoding.

ENV["LANG"]
#=> "UTF-8"
Encoding.default_external
#=> #<Encoding:UTF-8>

$ ruby -E ISO-8859-1 -e "p Encoding.default_external"
#<Encoding:ISO-8859-1>

$ LANG=C ruby -e 'p Encoding.default_external'
#<Encoding:US-ASCII>

The default external encoding may also be set through Encoding.default_external=, but you should not do this as strings created before and after the change will have inconsistent encodings. Instead use ruby -E to invoke ruby with the correct external encoding.

When you know that the actual encoding of the data of an IO object is not the default external encoding, you can reset its external encoding with IO#set_encoding or set it at IO object creation (see IO.new options).

Internal encoding

To process the data of an IO object which has an encoding different from its external encoding, you can set its internal encoding. Ruby will use this internal encoding to transcode the data when it is read from the IO object.

Conversely, when data is written to the IO object it is transcoded from the internal encoding to the external encoding of the IO object.

The internal encoding of an IO object can be set with IO#set_encoding or at IO object creation (see IO.new options).

The internal encoding is optional and when not set, the Ruby default internal encoding is used. If not explicitly set this default internal encoding is nil meaning that by default, no transcoding occurs.

The default internal encoding can be set with the interpreter option -E. Encoding.default_internal returns the current internal encoding.

$ ruby -e 'p Encoding.default_internal'
nil

$ ruby -E ISO-8859-1:UTF-8 -e "p [Encoding.default_external, \
  Encoding.default_internal]"
[#<Encoding:ISO-8859-1>, #<Encoding:UTF-8>]

The default internal encoding may also be set through Encoding.default_internal=, but you should not do this as strings created before and after the change will have inconsistent encodings. Instead use ruby -E to invoke ruby with the correct internal encoding.

IO encoding example

In the following example a UTF-8 encoded string "Ru00E9sumu00E9" is transcoded for output to ISO-8859-1 encoding, then read back in and transcoded to UTF-8:

string = "R\u00E9sum\u00E9"

open("transcoded.txt", "w:ISO-8859-1") do |io|
  io.write(string)
end

puts "raw text:"
p File.binread("transcoded.txt")
puts

open("transcoded.txt", "r:ISO-8859-1:UTF-8") do |io|
  puts "transcoded text:"
  p io.read
end

While writing the file, the internal encoding is not specified as it is only necessary for reading. While reading the file both the internal and external encoding must be specified to obtain the correct result.

$ ruby t.rb
raw text:
"R\xE9sum\xE9"

transcoded text:
"R\u00E9sum\u00E9"

Defined Under Namespace

Classes: CompatibilityError, Converter, ConverterNotFoundError, InvalidByteSequenceError, UndefinedConversionError

Class Method Summary collapse

Instance Method Summary collapse

Class Method Details

._load ⇒ Object

:nodoc:



1144
1145
1146
1147
1148
 
# File 'encoding.c', line 1144

static VALUE
enc_load(VALUE klass, VALUE str)
{
    return enc_find(klass, str);
}

.aliases ⇒ Object

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

Encoding.aliases
#=> {"BINARY"=>"ASCII-8BIT", "ASCII"=>"US-ASCII", "ANSI_X3.4-1986"=>"US-ASCII",
      "SJIS"=>"Shift_JIS", "eucJP"=>"EUC-JP", "CP932"=>"Windows-31J"}



1624
1625
1626
1627
1628
1629
1630
1631
1632
 
# File 'encoding.c', line 1624

static VALUE
rb_enc_aliases(VALUE klass)
{
    VALUE aliases[2];
    aliases[0] = rb_hash_new();
    aliases[1] = rb_ary_new();
    st_foreach(enc_table.names, rb_enc_aliases_enc_i, (st_data_t)aliases);
    return aliases[0];
}

.compatible?(obj1, obj2) ⇒ nil

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

Returns:

  • (nil)

Returns:

  • (Boolean) 


1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
 
# File 'encoding.c', line 1123

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);
}

.default_external ⇒ Object

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.

The default external encoding is initialized by the locale or -E option.



1331
1332
1333
1334
1335
 
# File 'encoding.c', line 1331

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

.default_external=(enc) ⇒ Object

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.



1360
1361
1362
1363
1364
1365
1366
 
# File 'encoding.c', line 1360

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

.default_internal ⇒ Object

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 Curses

  • Strings returned from Readline

  • Strings returned from SDBM

  • Time#zone

  • Values from ENV

  • Values in ARGV including $PROGRAM_NAME

  • __FILE__

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

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

Encoding::default_internal is initialized by the source file's internal_encoding or -E option.



1417
1418
1419
1420
1421
 
# File 'encoding.c', line 1417

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

.default_internal=(enc) ⇒ Object

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.



1443
1444
1445
1446
1447
1448
1449
 
# File 'encoding.c', line 1443

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

.find(string) ⇒ Object .find(symbol) ⇒ Object

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

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

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.



1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
 
# File 'encoding.c', line 1088

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

.list ⇒ Array

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)>]

Returns:



1056
1057
1058
1059
1060
1061
1062
 
# File 'encoding.c', line 1056

static VALUE
enc_list(VALUE klass)
{
    VALUE ary = rb_ary_new2(0);
    rb_ary_replace(ary, rb_encoding_list);
    return ary;
}

.locale_charmap ⇒ String

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.

Returns:



1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
 
# File 'encoding.c', line 1476

VALUE
rb_locale_charmap(VALUE klass)
{
#if defined NO_LOCALE_CHARMAP
    return rb_usascii_str_new2("ASCII-8BIT");
#elif defined _WIN32 || defined __CYGWIN__
    const char *codeset = 0;
    char cp[sizeof(int) * 3 + 4];
# ifdef __CYGWIN__
    const char *nl_langinfo_codeset(void);
    codeset = nl_langinfo_codeset();
# endif
    if (!codeset) {
	UINT codepage = GetConsoleCP();
	if (!codepage) codepage = GetACP();
	snprintf(cp, sizeof(cp), "CP%d", codepage);
	codeset = cp;
    }
    return rb_usascii_str_new2(codeset);
#elif defined HAVE_LANGINFO_H
    char *codeset;
    codeset = nl_langinfo(CODESET);
    return rb_usascii_str_new2(codeset);
#else
    return Qnil;
#endif
}

.name_list ⇒ Array

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"]

Returns:



1579
1580
1581
1582
1583
1584
1585
 
# File 'encoding.c', line 1579

static VALUE
rb_enc_name_list(VALUE klass)
{
    VALUE 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;
}

Instance Method Details

#_dump ⇒ Object

:nodoc:



1136
1137
1138
1139
1140
1141
 
# File 'encoding.c', line 1136

static VALUE
enc_dump(int argc, VALUE *argv, VALUE self)
{
    rb_scan_args(argc, argv, "01", 0);
    return enc_name(self);
}

#ascii_compatible? ⇒ Boolean

Returns whether ASCII-compatible or not.

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

Returns:

  • (Boolean)

Returns:

  • (Boolean) 


449
450
451
452
453
 
# File 'encoding.c', line 449

static VALUE
enc_ascii_compatible_p(VALUE enc)
{
    return rb_enc_asciicompat(enc_table.list[must_encoding(enc)].enc) ? Qtrue : Qfalse;
}

#dummy? ⇒ Boolean

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

Returns:

  • (Boolean)

Returns:

  • (Boolean) 


433
434
435
436
437
 
# File 'encoding.c', line 433

static VALUE
enc_dummy_p(VALUE enc)
{
    return ENC_DUMMY_P(enc_table.list[must_encoding(enc)].enc) ? Qtrue : Qfalse;
}

#inspect ⇒ String

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)>"

Returns:



982
983
984
985
986
987
988
989
990
 
# File 'encoding.c', line 982

static VALUE
enc_inspect(VALUE self)
{
    VALUE str = rb_sprintf("#<%s:%s%s>", rb_obj_classname(self),
		      rb_enc_name((rb_encoding*)DATA_PTR(self)),
		      (enc_dummy_p(self) ? " (dummy)" : ""));
    ENCODING_CODERANGE_SET(str, rb_usascii_encindex(), ENC_CODERANGE_7BIT);
    return str;
}

#name ⇒ String

Returns the name of the encoding.

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

Returns:



1000
1001
1002
1003
1004
 
# File 'encoding.c', line 1000

static VALUE
enc_name(VALUE self)
{
    return rb_usascii_str_new2(rb_enc_name((rb_encoding*)DATA_PTR(self)));
}

#names ⇒ Array

Returns the list of name and aliases of the encoding.

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

Returns:



1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
 
# File 'encoding.c', line 1027

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

    args[0] = (VALUE)rb_to_encoding_index(self);
    args[1] = rb_ary_new2(0);
    st_foreach(enc_table.names, enc_names_i, (st_data_t)args);
    return args[1];
}

#replicate(name) ⇒ Encoding

Returns a replicated encoding of enc whose name is name. The new encoding should have the same byte structure of enc. If name is used by another encoding, raise ArgumentError.

Returns:



363
364
365
366
367
368
369
 
# File 'encoding.c', line 363

static VALUE
enc_replicate(VALUE encoding, VALUE name)
{
    return rb_enc_from_encoding_index(
	rb_enc_replicate(StringValueCStr(name),
			 rb_to_encoding(encoding)));
}

#name ⇒ String

Returns the name of the encoding.

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

Returns:



1000
1001
1002
1003
1004
 
# File 'encoding.c', line 1000

static VALUE
enc_name(VALUE self)
{
    return rb_usascii_str_new2(rb_enc_name((rb_encoding*)DATA_PTR(self)));
}