3 perlunicode - Unicode support in Perl
7 =head2 Important Caveats
9 Unicode support is an extensive requirement. While perl does not
10 implement the Unicode standard or the accompanying technical reports
11 from cover to cover, Perl does support many Unicode features.
15 =item Input and Output Disciplines
17 A filehandle can be marked as containing perl's internal Unicode
18 encoding (UTF-8 or UTF-EBCDIC) by opening it with the ":utf8" layer.
19 Other encodings can be converted to perl's encoding on input, or from
20 perl's encoding on output by use of the ":encoding(...)" layer.
23 To mark the Perl source itself as being in a particular encoding,
26 =item Regular Expressions
28 The regular expression compiler produces polymorphic opcodes. That is,
29 the pattern adapts to the data and automatically switch to the Unicode
30 character scheme when presented with Unicode data, or a traditional
31 byte scheme when presented with byte data.
33 =item C<use utf8> still needed to enable UTF-8/UTF-EBCDIC in scripts
35 As a compatibility measure, this pragma must be explicitly used to
36 enable recognition of UTF-8 in the Perl scripts themselves on ASCII
37 based machines, or to recognize UTF-EBCDIC on EBCDIC based machines.
38 B<NOTE: this should be the only place where an explicit C<use utf8>
41 You can also use the C<encoding> pragma to change the default encoding
42 of the data in your script; see L<encoding>.
46 =head2 Byte and Character semantics
48 Beginning with version 5.6, Perl uses logically wide characters to
49 represent strings internally.
51 In future, Perl-level operations can be expected to work with
52 characters rather than bytes, in general.
54 However, as strictly an interim compatibility measure, Perl aims to
55 provide a safe migration path from byte semantics to character
56 semantics for programs. For operations where Perl can unambiguously
57 decide that the input data is characters, Perl now switches to
58 character semantics. For operations where this determination cannot
59 be made without additional information from the user, Perl decides in
60 favor of compatibility, and chooses to use byte semantics.
62 This behavior preserves compatibility with earlier versions of Perl,
63 which allowed byte semantics in Perl operations, but only as long as
64 none of the program's inputs are marked as being as source of Unicode
65 character data. Such data may come from filehandles, from calls to
66 external programs, from information provided by the system (such as %ENV),
67 or from literals and constants in the source text.
69 On Windows platforms, if the C<-C> command line switch is used, (or the
70 ${^WIDE_SYSTEM_CALLS} global flag is set to C<1>), all system calls
71 will use the corresponding wide character APIs. Note that this is
72 currently only implemented on Windows since other platforms lack an
73 API standard on this area.
75 Regardless of the above, the C<bytes> pragma can always be used to
76 force byte semantics in a particular lexical scope. See L<bytes>.
78 The C<utf8> pragma is primarily a compatibility device that enables
79 recognition of UTF-(8|EBCDIC) in literals encountered by the parser.
80 Note that this pragma is only required until a future version of Perl
81 in which character semantics will become the default. This pragma may
82 then become a no-op. See L<utf8>.
84 Unless mentioned otherwise, Perl operators will use character semantics
85 when they are dealing with Unicode data, and byte semantics otherwise.
86 Thus, character semantics for these operations apply transparently; if
87 the input data came from a Unicode source (for example, by adding a
88 character encoding discipline to the filehandle whence it came, or a
89 literal Unicode string constant in the program), character semantics
90 apply; otherwise, byte semantics are in effect. To force byte semantics
91 on Unicode data, the C<bytes> pragma should be used.
93 Notice that if you concatenate strings with byte semantics and strings
94 with Unicode character data, the bytes will by default be upgraded
95 I<as if they were ISO 8859-1 (Latin-1)> (or if in EBCDIC, after a
96 translation to ISO 8859-1). This is done without regard to the
97 system's native 8-bit encoding, so to change this for systems with
98 non-Latin-1 (or non-EBCDIC) native encodings, use the C<encoding>
99 pragma, see L<encoding>.
101 Under character semantics, many operations that formerly operated on
102 bytes change to operating on characters. A character in Perl is
103 logically just a number ranging from 0 to 2**31 or so. Larger
104 characters may encode to longer sequences of bytes internally, but
105 this is just an internal detail which is hidden at the Perl level.
106 See L<perluniintro> for more on this.
108 =head2 Effects of character semantics
110 Character semantics have the following effects:
116 Strings and patterns may contain characters that have an ordinal value
119 If you use a Unicode editor to edit your program, Unicode characters
120 may occur directly within the literal strings in one of the various
121 Unicode encodings (UTF-8, UTF-EBCDIC, UCS-2, etc.), but are recognized
122 as such (and converted to Perl's internal representation) only if the
123 appropriate L<encoding> is specified.
125 You can also get Unicode characters into a string by using the C<\x{...}>
126 notation, putting the Unicode code for the desired character, in
127 hexadecimal, into the curlies. For instance, a smiley face is C<\x{263A}>.
128 This works only for characters with a code 0x100 and above.
131 use charnames ':full';
132 you can use the C<\N{...}> notation, putting the official Unicode character
133 name within the curlies. For example, C<\N{WHITE SMILING FACE}>.
134 This works for all characters that have names.
138 If an appropriate L<encoding> is specified,
139 identifiers within the Perl script may contain Unicode alphanumeric
140 characters, including ideographs. (You are currently on your own when
141 it comes to using the canonical forms of characters--Perl doesn't
142 (yet) attempt to canonicalize variable names for you.)
146 Regular expressions match characters instead of bytes. For instance,
147 "." matches a character instead of a byte. (However, the C<\C> pattern
148 is provided to force a match a single byte ("C<char>" in C, hence C<\C>).)
152 Character classes in regular expressions match characters instead of
153 bytes, and match against the character properties specified in the
154 Unicode properties database. So C<\w> can be used to match an
155 ideograph, for instance.
159 Named Unicode properties, scripts, and block ranges may be used like
160 character classes via the new C<\p{}> (matches property) and C<\P{}>
161 (doesn't match property) constructs. For instance, C<\p{Lu}> matches any
162 character with the Unicode "Lu" (Letter, uppercase) property, while
163 C<\p{M}> matches any character with a "M" (mark -- accents and such)
164 property. Single letter properties may omit the brackets, so that can be
165 written C<\pM> also. Many predefined properties are available, such
166 as C<\p{Mirrored}> and C<\p{Tibetan}>.
168 The official Unicode script and block names have spaces and dashes as
169 separators, but for convenience you can have dashes, spaces, and underbars
170 at every word division, and you need not care about correct casing. It is
171 recommended, however, that for consistency you use the following naming:
172 the official Unicode script, block, or property name (see below for the
173 additional rules that apply to block names), with whitespace and dashes
174 removed, and the words "uppercase-first-lowercase-rest". That is, "Latin-1
175 Supplement" becomes "Latin1Supplement".
177 You can also negate both C<\p{}> and C<\P{}> by introducing a caret
178 (^) between the first curly and the property name: C<\p{^Tamil}> is
179 equal to C<\P{Tamil}>.
181 Here are the basic Unicode General Category properties, followed by their
182 long form (you can use either, e.g. C<\p{Lu}> and C<\p{LowercaseLetter}>
205 Pc ConnectorPunctuation
209 Pi InitialPunctuation
210 (may behave like Ps or Pe depending on usage)
212 (may behave like Ps or Pe depending on usage)
224 Zp ParagraphSeparator
229 Cs Surrogate (not usable)
233 The single-letter properties match all characters in any of the
234 two-letter sub-properties starting with the same letter.
235 There's also C<L&> which is an alias for C<Ll>, C<Lu>, and C<Lt>.
237 Because Perl hides the need for the user to understand the internal
238 representation of Unicode characters, it has no need to support the
239 somewhat messy concept of surrogates. Therefore, the C<Cs> property is not
242 Because scripts differ in their directionality (for example Hebrew is
243 written right to left), Unicode supplies these properties:
248 BidiLRE Left-to-Right Embedding
249 BidiLRO Left-to-Right Override
251 BidiAL Right-to-Left Arabic
252 BidiRLE Right-to-Left Embedding
253 BidiRLO Right-to-Left Override
254 BidiPDF Pop Directional Format
255 BidiEN European Number
256 BidiES European Number Separator
257 BidiET European Number Terminator
259 BidiCS Common Number Separator
260 BidiNSM Non-Spacing Mark
261 BidiBN Boundary Neutral
262 BidiB Paragraph Separator
263 BidiS Segment Separator
265 BidiON Other Neutrals
267 For example, C<\p{BidiR}> matches all characters that are normally
268 written right to left.
274 The scripts available via C<\p{...}> and C<\P{...}>, for example
275 C<\p{Latin}> or \p{Cyrillic>, are as follows:
318 There are also extended property classes that supplement the basic
319 properties, defined by the F<PropList> Unicode database:
330 NoncharacterCodePoint
338 and further derived properties:
340 Alphabetic Lu + Ll + Lt + Lm + Lo + OtherAlphabetic
341 Lowercase Ll + OtherLowercase
342 Uppercase Lu + OtherUppercase
345 ID_Start Lu + Ll + Lt + Lm + Lo + Nl
346 ID_Continue ID_Start + Mn + Mc + Nd + Pc
349 Assigned Any non-Cn character (i.e. synonym for C<\P{Cn}>)
350 Unassigned Synonym for C<\p{Cn}>
351 Common Any character (or unassigned code point)
352 not explicitly assigned to a script
354 For backward compatability, all properties mentioned so far may have C<Is>
355 prepended to their name (e.g. C<\P{IsLu}> is equal to C<\P{Lu}>).
359 In addition to B<scripts>, Unicode also defines B<blocks> of characters.
360 The difference between scripts and blocks is that the scripts concept is
361 closer to natural languages, while the blocks concept is more an artificial
362 grouping based on groups of mostly 256 Unicode characters. For example, the
363 C<Latin> script contains letters from many blocks. On the other hand, the
364 C<Latin> script does not contain all the characters from those blocks. It
365 does not, for example, contain digits because digits are shared across many
366 scripts. Digits and other similar groups, like punctuation, are in a
367 category called C<Common>.
369 For more about scripts, see the UTR #24:
371 http://www.unicode.org/unicode/reports/tr24/
373 For more about blocks, see:
375 http://www.unicode.org/Public/UNIDATA/Blocks.txt
377 Blocks names are given with the C<In> prefix. For example, the
378 Katakana block is referenced via C<\p{InKatakana}>. The C<In>
379 prefix may be omitted if there is no nameing conflict with a script
380 or any other property, but it is recommended that C<In> always be used
383 These block names are supported:
385 InAlphabeticPresentationForms
387 InArabicPresentationFormsA
388 InArabicPresentationFormsB
398 InByzantineMusicalSymbols
400 InCJKCompatibilityForms
401 InCJKCompatibilityIdeographs
402 InCJKCompatibilityIdeographsSupplement
403 InCJKRadicalsSupplement
404 InCJKSymbolsAndPunctuation
405 InCJKUnifiedIdeographs
406 InCJKUnifiedIdeographsExtensionA
407 InCJKUnifiedIdeographsExtensionB
409 InCombiningDiacriticalMarks
411 InCombiningMarksForSymbols
418 InEnclosedAlphanumerics
419 InEnclosedCJKLettersAndMonths
429 InHalfwidthAndFullwidthForms
430 InHangulCompatibilityJamo
434 InHighPrivateUseSurrogates
438 InIdeographicDescriptionCharacters
446 InLatinExtendedAdditional
452 InMathematicalAlphanumericSymbols
453 InMathematicalOperators
454 InMiscellaneousSymbols
455 InMiscellaneousTechnical
462 InOpticalCharacterRecognition
468 InSpacingModifierLetters
470 InSuperscriptsAndSubscripts
478 InUnifiedCanadianAboriginalSyllabics
486 The special pattern C<\X> matches any extended Unicode sequence
487 (a "combining character sequence" in Standardese), where the first
488 character is a base character and subsequent characters are mark
489 characters that apply to the base character. It is equivalent to
494 The C<tr///> operator translates characters instead of bytes. Note
495 that the C<tr///CU> functionality has been removed, as the interface
496 was a mistake. For similar functionality see pack('U0', ...) and
501 Case translation operators use the Unicode case translation tables
502 when provided character input. Note that C<uc()> (also known as C<\U>
503 in doublequoted strings) translates to uppercase, while C<ucfirst>
504 (also known as C<\u> in doublequoted strings) translates to titlecase
505 (for languages that make the distinction). Naturally the
506 corresponding backslash sequences have the same semantics.
510 Most operators that deal with positions or lengths in the string will
511 automatically switch to using character positions, including
512 C<chop()>, C<substr()>, C<pos()>, C<index()>, C<rindex()>,
513 C<sprintf()>, C<write()>, and C<length()>. Operators that
514 specifically don't switch include C<vec()>, C<pack()>, and
515 C<unpack()>. Operators that really don't care include C<chomp()>, as
516 well as any other operator that treats a string as a bucket of bits,
517 such as C<sort()>, and the operators dealing with filenames.
521 The C<pack()>/C<unpack()> letters "C<c>" and "C<C>" do I<not> change,
522 since they're often used for byte-oriented formats. (Again, think
523 "C<char>" in the C language.) However, there is a new "C<U>" specifier
524 that will convert between Unicode characters and integers.
528 The C<chr()> and C<ord()> functions work on characters. This is like
529 C<pack("U")> and C<unpack("U")>, not like C<pack("C")> and
530 C<unpack("C")>. In fact, the latter are how you now emulate
531 byte-oriented C<chr()> and C<ord()> for Unicode strings.
532 (Note that this reveals the internal encoding of Unicode strings,
533 which is not something one normally needs to care about at all.)
537 The bit string operators C<& | ^ ~> can operate on character data.
538 However, for backward compatibility reasons (bit string operations
539 when the characters all are less than 256 in ordinal value) one should
540 not mix C<~> (the bit complement) and characters both less than 256 and
541 equal or greater than 256. Most importantly, the DeMorgan's laws
542 (C<~($x|$y) eq ~$x&~$y>, C<~($x&$y) eq ~$x|~$y>) won't hold.
543 Another way to look at this is that the complement cannot return
544 B<both> the 8-bit (byte) wide bit complement B<and> the full character
549 lc(), uc(), lcfirst(), and ucfirst() work for the following cases:
555 the case mapping is from a single Unicode character to another
556 single Unicode character
560 the case mapping is from a single Unicode character to more
561 than one Unicode character
565 What doesn't yet work are the following cases:
571 the "final sigma" (Greek)
575 anything to with locales (Lithuanian, Turkish, Azeri)
579 See the Unicode Technical Report #21, Case Mappings, for more details.
583 And finally, C<scalar reverse()> reverses by character rather than by byte.
587 =head2 Character encodings for input and output
591 =head2 Unicode Regular Expression Support Level
593 The following list of Unicode regular expression support describes
594 feature by feature the Unicode support implemented in Perl as of Perl
595 5.8.0. The "Level N" and the section numbers refer to the Unicode
596 Technical Report 18, "Unicode Regular Expression Guidelines".
602 Level 1 - Basic Unicode Support
604 2.1 Hex Notation - done [1]
605 Named Notation - done [2]
606 2.2 Categories - done [3][4]
607 2.3 Subtraction - MISSING [5][6]
608 2.4 Simple Word Boundaries - done [7]
609 2.5 Simple Loose Matches - done [8]
610 2.6 End of Line - MISSING [9][10]
614 [ 3] . \p{...} \P{...}
615 [ 4] now scripts (see UTR#24 Script Names) in addition to blocks
617 [ 6] can use look-ahead to emulate subtraction (*)
618 [ 7] include Letters in word characters
619 [ 8] note that perl does Full casefolding in matching, not Simple:
620 for example U+1F88 is equivalent with U+1F000 U+03B9,
621 not with 1F80. This difference matters for certain Greek
622 capital letters with certain modifiers: the Full casefolding
623 decomposes the letter, while the Simple casefolding would map
624 it to a single character.
625 [ 9] see UTR#13 Unicode Newline Guidelines
626 [10] should do ^ and $ also on \x{85}, \x{2028} and \x{2029})
627 (should also affect <>, $., and script line numbers)
628 (the \x{85}, \x{2028} and \x{2029} do match \s)
630 (*) You can mimic class subtraction using lookahead.
631 For example, what TR18 might write as
633 [{Greek}-[{UNASSIGNED}]]
635 in Perl can be written as:
637 (?!\p{Unassigned})\p{InGreek}
638 (?=\p{Assigned})\p{InGreek}
640 But in this particular example, you probably really want
644 which will match assigned characters known to be part of the Greek script.
648 Level 2 - Extended Unicode Support
650 3.1 Surrogates - MISSING
651 3.2 Canonical Equivalents - MISSING [11][12]
652 3.3 Locale-Independent Graphemes - MISSING [13]
653 3.4 Locale-Independent Words - MISSING [14]
654 3.5 Locale-Independent Loose Matches - MISSING [15]
656 [11] see UTR#15 Unicode Normalization
657 [12] have Unicode::Normalize but not integrated to regexes
658 [13] have \X but at this level . should equal that
659 [14] need three classes, not just \w and \W
660 [15] see UTR#21 Case Mappings
664 Level 3 - Locale-Sensitive Support
666 4.1 Locale-Dependent Categories - MISSING
667 4.2 Locale-Dependent Graphemes - MISSING [16][17]
668 4.3 Locale-Dependent Words - MISSING
669 4.4 Locale-Dependent Loose Matches - MISSING
670 4.5 Locale-Dependent Ranges - MISSING
672 [16] see UTR#10 Unicode Collation Algorithms
673 [17] have Unicode::Collate but not integrated to regexes
677 =head2 Unicode Encodings
679 Unicode characters are assigned to I<code points> which are abstract
680 numbers. To use these numbers various encodings are needed.
688 UTF-8 is a variable-length (1 to 6 bytes, current character allocations
689 require 4 bytes), byteorder independent encoding. For ASCII, UTF-8 is
690 transparent (and we really do mean 7-bit ASCII, not another 8-bit encoding).
692 The following table is from Unicode 3.2.
694 Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte
696 U+0000..U+007F 00..7F
697 U+0080..U+07FF C2..DF 80..BF
698 U+0800..U+0FFF E0 A0..BF 80..BF
699 U+1000..U+CFFF E1..EC 80..BF 80..BF
700 U+D000..U+D7FF ED 80..9F 80..BF
701 U+D800..U+DFFF ******* ill-formed *******
702 U+E000..U+FFFF EE..EF 80..BF 80..BF
703 U+10000..U+3FFFF F0 90..BF 80..BF 80..BF
704 U+40000..U+FFFFF F1..F3 80..BF 80..BF 80..BF
705 U+100000..U+10FFFF F4 80..8F 80..BF 80..BF
707 Note the A0..BF in U+0800..U+0FFF, the 80..9F in U+D000...U+D7FF,
708 the 90..BF in U+10000..U+3FFFF, and the 80...8F in U+100000..U+10FFFF.
709 Or, another way to look at it, as bits:
711 Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte
714 00000bbbbbaaaaaa 110bbbbb 10aaaaaa
715 ccccbbbbbbaaaaaa 1110cccc 10bbbbbb 10aaaaaa
716 00000dddccccccbbbbbbaaaaaa 11110ddd 10cccccc 10bbbbbb 10aaaaaa
718 As you can see, the continuation bytes all begin with C<10>, and the
719 leading bits of the start byte tell how many bytes the are in the
726 Like UTF-8, but EBCDIC-safe, as UTF-8 is ASCII-safe.
730 UTF-16, UTF-16BE, UTF16-LE, Surrogates, and BOMs (Byte Order Marks)
732 (The followings items are mostly for reference, Perl doesn't
733 use them internally.)
735 UTF-16 is a 2 or 4 byte encoding. The Unicode code points
736 0x0000..0xFFFF are stored in two 16-bit units, and the code points
737 0x010000..0x10FFFF in two 16-bit units. The latter case is
738 using I<surrogates>, the first 16-bit unit being the I<high
739 surrogate>, and the second being the I<low surrogate>.
741 Surrogates are code points set aside to encode the 0x01000..0x10FFFF
742 range of Unicode code points in pairs of 16-bit units. The I<high
743 surrogates> are the range 0xD800..0xDBFF, and the I<low surrogates>
744 are the range 0xDC00..0xDFFFF. The surrogate encoding is
746 $hi = ($uni - 0x10000) / 0x400 + 0xD800;
747 $lo = ($uni - 0x10000) % 0x400 + 0xDC00;
751 $uni = 0x10000 + ($hi - 0xD8000) * 0x400 + ($lo - 0xDC00);
753 If you try to generate surrogates (for example by using chr()), you
754 will get a warning if warnings are turned on (C<-w> or C<use
755 warnings;>) because those code points are not valid for a Unicode
758 Because of the 16-bitness, UTF-16 is byteorder dependent. UTF-16
759 itself can be used for in-memory computations, but if storage or
760 transfer is required, either UTF-16BE (Big Endian) or UTF-16LE
761 (Little Endian) must be chosen.
763 This introduces another problem: what if you just know that your data
764 is UTF-16, but you don't know which endianness? Byte Order Marks
765 (BOMs) are a solution to this. A special character has been reserved
766 in Unicode to function as a byte order marker: the character with the
767 code point 0xFEFF is the BOM.
769 The trick is that if you read a BOM, you will know the byte order,
770 since if it was written on a big endian platform, you will read the
771 bytes 0xFE 0xFF, but if it was written on a little endian platform,
772 you will read the bytes 0xFF 0xFE. (And if the originating platform
773 was writing in UTF-8, you will read the bytes 0xEF 0xBB 0xBF.)
775 The way this trick works is that the character with the code point
776 0xFFFE is guaranteed not to be a valid Unicode character, so the
777 sequence of bytes 0xFF 0xFE is unambiguously "BOM, represented in
778 little-endian format" and cannot be "0xFFFE, represented in big-endian
783 UTF-32, UTF-32BE, UTF32-LE
785 The UTF-32 family is pretty much like the UTF-16 family, expect that
786 the units are 32-bit, and therefore the surrogate scheme is not
787 needed. The BOM signatures will be 0x00 0x00 0xFE 0xFF for BE and
788 0xFF 0xFE 0x00 0x00 for LE.
794 Encodings defined by the ISO 10646 standard. UCS-2 is a 16-bit
795 encoding, UCS-4 is a 32-bit encoding. Unlike UTF-16, UCS-2
796 is not extensible beyond 0xFFFF, because it does not use surrogates.
802 A seven-bit safe (non-eight-bit) encoding, useful if the
803 transport/storage is not eight-bit safe. Defined by RFC 2152.
807 =head2 Security Implications of Malformed UTF-8
809 Unfortunately, the specification of UTF-8 leaves some room for
810 interpretation of how many bytes of encoded output one should generate
811 from one input Unicode character. Strictly speaking, one is supposed
812 to always generate the shortest possible sequence of UTF-8 bytes,
813 because otherwise there is potential for input buffer overflow at
814 the receiving end of a UTF-8 connection. Perl always generates the
815 shortest length UTF-8, and with warnings on (C<-w> or C<use
816 warnings;>) Perl will warn about non-shortest length UTF-8 (and other
817 malformations, too, such as the surrogates, which are not real
818 Unicode code points.)
820 =head2 Unicode in Perl on EBCDIC
822 The way Unicode is handled on EBCDIC platforms is still rather
823 experimental. On such a platform, references to UTF-8 encoding in this
824 document and elsewhere should be read as meaning UTF-EBCDIC as
825 specified in Unicode Technical Report 16 unless ASCII vs EBCDIC issues
826 are specifically discussed. There is no C<utfebcdic> pragma or
827 ":utfebcdic" layer, rather, "utf8" and ":utf8" are re-used to mean
828 the platform's "natural" 8-bit encoding of Unicode. See L<perlebcdic>
829 for more discussion of the issues.
833 Usually locale settings and Unicode do not affect each other, but
834 there are a couple of exceptions:
840 If your locale environment variables (LANGUAGE, LC_ALL, LC_CTYPE, LANG)
841 contain the strings 'UTF-8' or 'UTF8' (case-insensitive matching),
842 the default encoding of your STDIN, STDOUT, and STDERR, and of
843 B<any subsequent file open>, is UTF-8.
847 Perl tries really hard to work both with Unicode and the old byte
848 oriented world: most often this is nice, but sometimes this causes
849 problems. See L</BUGS> for example how sometimes using locales
850 with Unicode can help with these problems.
854 =head2 Using Unicode in XS
856 If you want to handle Perl Unicode in XS extensions, you may find
857 the following C APIs useful (see perlapi for details):
863 DO_UTF8(sv) returns true if the UTF8 flag is on and the bytes pragma
864 is not in effect. SvUTF8(sv) returns true is the UTF8 flag is on, the
865 bytes pragma is ignored. The UTF8 flag being on does B<not> mean that
866 there are any characters of code points greater than 255 (or 127) in
867 the scalar, or that there even are any characters in the scalar.
868 What the UTF8 flag means is that the sequence of octets in the
869 representation of the scalar is the sequence of UTF-8 encoded
870 code points of the characters of a string. The UTF8 flag being
871 off means that each octet in this representation encodes a single
872 character with codepoint 0..255 within the string. Perl's Unicode
873 model is not to use UTF-8 until it's really necessary.
877 uvuni_to_utf8(buf, chr) writes a Unicode character code point into a
878 buffer encoding the code point as UTF-8, and returns a pointer
879 pointing after the UTF-8 bytes.
883 utf8_to_uvuni(buf, lenp) reads UTF-8 encoded bytes from a buffer and
884 returns the Unicode character code point (and optionally the length of
885 the UTF-8 byte sequence).
889 utf8_length(start, end) returns the length of the UTF-8 encoded buffer
890 in characters. sv_len_utf8(sv) returns the length of the UTF-8 encoded
895 sv_utf8_upgrade(sv) converts the string of the scalar to its UTF-8
896 encoded form. sv_utf8_downgrade(sv) does the opposite (if possible).
897 sv_utf8_encode(sv) is like sv_utf8_upgrade but the UTF8 flag does not
898 get turned on. sv_utf8_decode() does the opposite of sv_utf8_encode().
899 Note that none of these are to be used as general purpose encoding/decoding
900 interfaces: use Encode for that. sv_utf8_upgrade() is affected by the
901 encoding pragma, but sv_utf8_downgrade() is not (since the encoding
902 pragma is designed to be a one-way street).
906 is_utf8_char(s) returns true if the pointer points to a valid UTF-8
911 is_utf8_string(buf, len) returns true if the len bytes of the buffer
916 UTF8SKIP(buf) will return the number of bytes in the UTF-8 encoded
917 character in the buffer. UNISKIP(chr) will return the number of bytes
918 required to UTF-8-encode the Unicode character code point. UTF8SKIP()
919 is useful for example for iterating over the characters of a UTF-8
920 encoded buffer; UNISKIP() is useful for example in computing
921 the size required for a UTF-8 encoded buffer.
925 utf8_distance(a, b) will tell the distance in characters between the
926 two pointers pointing to the same UTF-8 encoded buffer.
930 utf8_hop(s, off) will return a pointer to an UTF-8 encoded buffer that
931 is C<off> (positive or negative) Unicode characters displaced from the
932 UTF-8 buffer C<s>. Be careful not to overstep the buffer: utf8_hop()
933 will merrily run off the end or the beginning if told to do so.
937 pv_uni_display(dsv, spv, len, pvlim, flags) and sv_uni_display(dsv,
938 ssv, pvlim, flags) are useful for debug output of Unicode strings and
939 scalars. By default they are useful only for debug: they display
940 B<all> characters as hexadecimal code points, but with the flags
941 UNI_DISPLAY_ISPRINT and UNI_DISPLAY_BACKSLASH you can make the output
946 ibcmp_utf8(s1, pe1, u1, l1, u1, s2, pe2, l2, u2) can be used to
947 compare two strings case-insensitively in Unicode.
948 (For case-sensitive comparisons you can just use memEQ() and memNE()
953 For more information, see L<perlapi>, and F<utf8.c> and F<utf8.h>
954 in the Perl source code distribution.
958 Use of locales with Unicode data may lead to odd results. Currently
959 there is some attempt to apply 8-bit locale info to characters in the
960 range 0..255, but this is demonstrably incorrect for locales that use
961 characters above that range when mapped into Unicode. It will also
962 tend to run slower. Avoidance of locales is strongly encouraged,
963 with one known expection, see the next paragraph.
965 If the keys of a hash are "mixed", that is, some keys are Unicode,
966 while some keys are "byte", the keys may behave differently in regular
967 expressions since the definition of character classes like C</\w/>
968 is different for byte strings and character strings. This problem can
969 sometimes be helped by using an appropriate locale (see L<perllocale>).
970 Another way is to force all the strings to be character encoded by
971 using utf8::upgrade() (see L<utf8>).
973 Some functions are slower when working on UTF-8 encoded strings than
974 on byte encoded strings. All functions that need to hop over
975 characters such as length(), substr() or index() can work B<much>
976 faster when the underlying data are byte-encoded. Witness the
983 our $u = our $b = "x" x $l;
984 substr($u,0,1) = "\x{100}";
986 LENGTH_B => q{ length($b) },
987 LENGTH_U => q{ length($u) },
988 SUBSTR_B => q{ substr($b, $l/4, $l/2) },
989 SUBSTR_U => q{ substr($u, $l/4, $l/2) },
992 Benchmark: running LENGTH_B, LENGTH_U, SUBSTR_B, SUBSTR_U for at least 2 CPU seconds...
993 LENGTH_B: 2 wallclock secs ( 2.36 usr + 0.00 sys = 2.36 CPU) @ 5649983.05/s (n=13333960)
994 LENGTH_U: 2 wallclock secs ( 2.11 usr + 0.00 sys = 2.11 CPU) @ 12155.45/s (n=25648)
995 SUBSTR_B: 3 wallclock secs ( 2.16 usr + 0.00 sys = 2.16 CPU) @ 374480.09/s (n=808877)
996 SUBSTR_U: 2 wallclock secs ( 2.11 usr + 0.00 sys = 2.11 CPU) @ 6791.00/s (n=14329)
998 The numbers show an incredible slowness on long UTF-8 strings and you
999 should carefully avoid to use these functions within tight loops. For
1000 example if you want to iterate over characters, it is infinitely
1001 better to split into an array than to use substr, as the following
1008 our $u = our $b = "x" x $l;
1009 substr($u,0,1) = "\x{100}";
1011 SPLIT_B => q{ for my $c (split //, $b){} },
1012 SPLIT_U => q{ for my $c (split //, $u){} },
1013 SUBSTR_B => q{ for my $i (0..length($b)-1){my $c = substr($b,$i,1);} },
1014 SUBSTR_U => q{ for my $i (0..length($u)-1){my $c = substr($u,$i,1);} },
1017 Benchmark: running SPLIT_B, SPLIT_U, SUBSTR_B, SUBSTR_U for at least 5 CPU seconds...
1018 SPLIT_B: 6 wallclock secs ( 5.29 usr + 0.00 sys = 5.29 CPU) @ 56.14/s (n=297)
1019 SPLIT_U: 5 wallclock secs ( 5.17 usr + 0.01 sys = 5.18 CPU) @ 55.21/s (n=286)
1020 SUBSTR_B: 5 wallclock secs ( 5.34 usr + 0.00 sys = 5.34 CPU) @ 123.22/s (n=658)
1021 SUBSTR_U: 7 wallclock secs ( 6.20 usr + 0.00 sys = 6.20 CPU) @ 0.81/s (n=5)
1023 You see, the algorithm based on substr() was faster with byte encoded
1024 data but it is pathologically slow with UTF-8 data.
1028 L<perluniintro>, L<encoding>, L<Encode>, L<open>, L<utf8>, L<bytes>,
1029 L<perlretut>, L<perlvar/"${^WIDE_SYSTEM_CALLS}">
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