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 The C<utf8> pragma implements the tables used for Unicode support.
36 However, these tables are automatically loaded on demand, so the
37 C<utf8> pragma should not normally be used.
39 As a compatibility measure, this pragma must be explicitly used to
40 enable recognition of UTF-8 in the Perl scripts themselves on ASCII
41 based machines or recognize UTF-EBCDIC on EBCDIC based machines.
42 B<NOTE: this should be the only place where an explicit C<use utf8>
45 You can also use the C<encoding> pragma to change the default encoding
46 of the data in your script; see L<encoding>.
50 =head2 Byte and Character semantics
52 Beginning with version 5.6, Perl uses logically wide characters to
53 represent strings internally. This internal representation of strings
54 uses either the UTF-8 or the UTF-EBCDIC encoding.
56 In future, Perl-level operations can be expected to work with
57 characters rather than bytes, in general.
59 However, as strictly an interim compatibility measure, Perl aims to
60 provide a safe migration path from byte semantics to character
61 semantics for programs. For operations where Perl can unambiguously
62 decide that the input data is characters, Perl now switches to
63 character semantics. For operations where this determination cannot
64 be made without additional information from the user, Perl decides in
65 favor of compatibility, and chooses to use byte semantics.
67 This behavior preserves compatibility with earlier versions of Perl,
68 which allowed byte semantics in Perl operations, but only as long as
69 none of the program's inputs are marked as being as source of Unicode
70 character data. Such data may come from filehandles, from calls to
71 external programs, from information provided by the system (such as %ENV),
72 or from literals and constants in the source text.
74 On Windows platforms, if the C<-C> command line switch is used, (or the
75 ${^WIDE_SYSTEM_CALLS} global flag is set to C<1>), all system calls
76 will use the corresponding wide character APIs. Note that this is
77 currently only implemented on Windows since other platforms lack an
78 API standard on this area.
80 Regardless of the above, the C<bytes> pragma can always be used to
81 force byte semantics in a particular lexical scope. See L<bytes>.
83 The C<utf8> pragma is primarily a compatibility device that enables
84 recognition of UTF-(8|EBCDIC) in literals encountered by the parser.
85 Note that this pragma is only required until a future version of Perl
86 in which character semantics will become the default. This pragma may
87 then become a no-op. See L<utf8>.
89 Unless mentioned otherwise, Perl operators will use character semantics
90 when they are dealing with Unicode data, and byte semantics otherwise.
91 Thus, character semantics for these operations apply transparently; if
92 the input data came from a Unicode source (for example, by adding a
93 character encoding discipline to the filehandle whence it came, or a
94 literal UTF-8 string constant in the program), character semantics
95 apply; otherwise, byte semantics are in effect. To force byte semantics
96 on Unicode data, the C<bytes> pragma should be used.
98 Notice that if you concatenate strings with byte semantics and strings
99 with Unicode character data, the bytes will by default be upgraded
100 I<as if they were ISO 8859-1 (Latin-1)> (or if in EBCDIC, after a
101 translation to ISO 8859-1). To change this, use the C<encoding>
102 pragma, see L<encoding>.
104 Under character semantics, many operations that formerly operated on
105 bytes change to operating on characters. For ASCII data this makes no
106 difference, because UTF-8 stores ASCII in single bytes, but for any
107 character greater than C<chr(127)>, the character B<may> be stored in
108 a sequence of two or more bytes, all of which have the high bit set.
110 For C1 controls or Latin 1 characters on an EBCDIC platform the
111 character may be stored in a UTF-EBCDIC multi byte sequence. But by
112 and large, the user need not worry about this, because Perl hides it
113 from the user. A character in Perl is logically just a number ranging
114 from 0 to 2**32 or so. Larger characters encode to longer sequences
115 of bytes internally, but again, this is just an internal detail which
116 is hidden at the Perl level.
118 =head2 Effects of character semantics
120 Character semantics have the following effects:
126 Strings and patterns may contain characters that have an ordinal value
129 Presuming you use a Unicode editor to edit your program, such
130 characters will typically occur directly within the literal strings as
131 UTF-8 (or UTF-EBCDIC on EBCDIC platforms) characters, but you can also
132 specify a particular character with an extension of the C<\x>
133 notation. UTF-X characters are specified by putting the hexadecimal
134 code within curlies after the C<\x>. For instance, a Unicode smiley
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 and block ranges may be used as character
160 classes via the new C<\p{}> (matches property) and C<\P{}> (doesn't
161 match property) constructs. For instance, C<\p{Lu}> matches any
162 character with the Unicode uppercase property, while C<\p{M}> matches
163 any mark character. Single letter properties may omit the brackets,
164 so that can be written C<\pM> also. Many predefined character classes
165 are available, such as C<\p{IsMirrored}> and C<\p{InTibetan}>.
167 The C<\p{Is...}> test for "general properties" such as "letter",
168 "digit", while the C<\p{In...}> test for Unicode scripts and blocks.
170 The official Unicode script and block names have spaces and dashes as
171 separators, but for convenience you can have dashes, spaces, and
172 underbars at every word division, and you need not care about correct
173 casing. It is recommended, however, that for consistency you use the
174 following naming: the official Unicode script, block, or property name
175 (see below for the additional rules that apply to block names),
176 with whitespace and dashes replaced with underbar, and the words
177 "uppercase-first-lowercase-rest". That is, "Latin-1 Supplement"
178 becomes "Latin_1_Supplement".
180 You can also negate both C<\p{}> and C<\P{}> by introducing a caret
181 (^) between the first curly and the property name: C<\p{^In_Tamil}> is
182 equal to C<\P{In_Tamil}>.
184 The C<In> and C<Is> can be left out: C<\p{Greek}> is equal to
185 C<\p{In_Greek}>, C<\P{Pd}> is equal to C<\P{Pd}>.
207 Pc Connector_Punctuation
211 Pi Initial_Punctuation
212 (may behave like Ps or Pe depending on usage)
214 (may behave like Ps or Pe depending on usage)
226 Zp Paragraph_Separator
235 There's also C<L&> which is an alias for C<Ll>, C<Lu>, and C<Lt>.
237 The following reserved ranges have C<In> tests:
239 CJK_Ideograph_Extension_A
242 Non_Private_Use_High_Surrogate
243 Private_Use_High_Surrogate
246 CJK_Ideograph_Extension_B
250 For example C<"\x{AC00}" =~ \p{HangulSyllable}> will test true.
251 (Handling of surrogates is not implemented yet, because Perl
252 uses UTF-8 and not UTF-16 internally to represent Unicode.
253 So you really can't use the "Cs" category.)
255 Additionally, because scripts differ in their directionality
256 (for example Hebrew is written right to left), all characters
257 have their directionality defined:
260 BidiLRE Left-to-Right Embedding
261 BidiLRO Left-to-Right Override
263 BidiAL Right-to-Left Arabic
264 BidiRLE Right-to-Left Embedding
265 BidiRLO Right-to-Left Override
266 BidiPDF Pop Directional Format
267 BidiEN European Number
268 BidiES European Number Separator
269 BidiET European Number Terminator
271 BidiCS Common Number Separator
272 BidiNSM Non-Spacing Mark
273 BidiBN Boundary Neutral
274 BidiB Paragraph Separator
275 BidiS Segment Separator
277 BidiON Other Neutrals
283 The scripts available for C<\p{In...}> and C<\P{In...}>, for example
284 C<\p{InLatin}> or \p{InCyrillic>, are as follows:
327 There are also extended property classes that supplement the basic
328 properties, defined by the F<PropList> Unicode database:
339 Noncharacter_Code_Point
347 and further derived properties:
349 Alphabetic Lu + Ll + Lt + Lm + Lo + Other_Alphabetic
350 Lowercase Ll + Other_Lowercase
351 Uppercase Lu + Other_Uppercase
354 ID_Start Lu + Ll + Lt + Lm + Lo + Nl
355 ID_Continue ID_Start + Mn + Mc + Nd + Pc
358 Assigned Any non-Cn character
359 Common Any character (or unassigned code point)
360 not explicitly assigned to a script
364 In addition to B<scripts>, Unicode also defines B<blocks> of
365 characters. The difference between scripts and blocks is that the
366 scripts concept is closer to natural languages, while the blocks
367 concept is more an artificial grouping based on groups of 256 Unicode
368 characters. For example, the C<Latin> script contains letters from
369 many blocks. On the other hand, the C<Latin> script does not contain
370 all the characters from those blocks. It does not, for example, contain
371 digits because digits are shared across many scripts. Digits and
372 other similar groups, like punctuation, are in a category called
375 For more about scripts, see the UTR #24:
377 http://www.unicode.org/unicode/reports/tr24/
379 For more about blocks, see:
381 http://www.unicode.org/Public/UNIDATA/Blocks.txt
383 Because there are overlaps in naming (there are, for example, both
384 a script called C<Katakana> and a block called C<Katakana>, the block
385 version has C<Block> appended to its name, C<\p{InKatakanaBlock}>.
387 Notice that this definition was introduced in Perl 5.8.0: in Perl
388 5.6 only the blocks were used; in Perl 5.8.0 scripts became the
389 preferential Unicode character class definition; this meant that
390 the definitions of some character classes changed (the ones in the
391 below list that have the C<Block> appended).
393 Alphabetic Presentation Forms
395 Arabic Presentation Forms-A
396 Arabic Presentation Forms-B
406 Byzantine Musical Symbols
408 CJK Compatibility Forms
409 CJK Compatibility Ideographs
410 CJK Compatibility Ideographs Supplement
411 CJK Radicals Supplement
412 CJK Symbols and Punctuation
413 CJK Unified Ideographs
414 CJK Unified Ideographs Extension A
415 CJK Unified Ideographs Extension B
417 Combining Diacritical Marks
419 Combining Marks for Symbols
426 Enclosed Alphanumerics
427 Enclosed CJK Letters and Months
437 Halfwidth and Fullwidth Forms
438 Hangul Compatibility Jamo
442 High Private Use Surrogates
446 Ideographic Description Characters
454 Latin Extended Additional
460 Mathematical Alphanumeric Symbols
461 Mathematical Operators
462 Miscellaneous Symbols
463 Miscellaneous Technical
470 Optical Character Recognition
476 Spacing Modifier Letters
478 Superscripts and Subscripts
486 Unified Canadian Aboriginal Syllabics
494 The special pattern C<\X> match matches any extended Unicode sequence
495 (a "combining character sequence" in Standardese), where the first
496 character is a base character and subsequent characters are mark
497 characters that apply to the base character. It is equivalent to
502 The C<tr///> operator translates characters instead of bytes. Note
503 that the C<tr///CU> functionality has been removed, as the interface
504 was a mistake. For similar functionality see pack('U0', ...) and
509 Case translation operators use the Unicode case translation tables
510 when provided character input. Note that C<uc()> (also known as C<\U>
511 in doublequoted strings) translates to uppercase, while C<ucfirst>
512 (also known as C<\u> in doublequoted strings) translates to titlecase
513 (for languages that make the distinction). Naturally the
514 corresponding backslash sequences have the same semantics.
518 Most operators that deal with positions or lengths in the string will
519 automatically switch to using character positions, including
520 C<chop()>, C<substr()>, C<pos()>, C<index()>, C<rindex()>,
521 C<sprintf()>, C<write()>, and C<length()>. Operators that
522 specifically don't switch include C<vec()>, C<pack()>, and
523 C<unpack()>. Operators that really don't care include C<chomp()>, as
524 well as any other operator that treats a string as a bucket of bits,
525 such as C<sort()>, and the operators dealing with filenames.
529 The C<pack()>/C<unpack()> letters "C<c>" and "C<C>" do I<not> change,
530 since they're often used for byte-oriented formats. (Again, think
531 "C<char>" in the C language.) However, there is a new "C<U>" specifier
532 that will convert between UTF-8 characters and integers. (It works
533 outside of the utf8 pragma too.)
537 The C<chr()> and C<ord()> functions work on characters. This is like
538 C<pack("U")> and C<unpack("U")>, not like C<pack("C")> and
539 C<unpack("C")>. In fact, the latter are how you now emulate
540 byte-oriented C<chr()> and C<ord()> for Unicode strings.
541 (Note that this reveals the internal UTF-8 encoding of strings and
542 you are not supposed to do that unless you know what you are doing.)
546 The bit string operators C<& | ^ ~> can operate on character data.
547 However, for backward compatibility reasons (bit string operations
548 when the characters all are less than 256 in ordinal value) one should
549 not mix C<~> (the bit complement) and characters both less than 256 and
550 equal or greater than 256. Most importantly, the DeMorgan's laws
551 (C<~($x|$y) eq ~$x&~$y>, C<~($x&$y) eq ~$x|~$y>) won't hold.
552 Another way to look at this is that the complement cannot return
553 B<both> the 8-bit (byte) wide bit complement B<and> the full character
558 lc(), uc(), lcfirst(), and ucfirst() work for the following cases:
564 the case mapping is from a single Unicode character to another
565 single Unicode character
569 the case mapping is from a single Unicode character to more
570 than one Unicode character
574 What doesn't yet work are the following cases:
580 the "final sigma" (Greek)
584 anything to with locales (Lithuanian, Turkish, Azeri)
588 See the Unicode Technical Report #21, Case Mappings, for more details.
592 And finally, C<scalar reverse()> reverses by character rather than by byte.
596 =head2 Character encodings for input and output
602 As of yet, there is no method for automatically coercing input and
603 output to some encoding other than UTF-8 or UTF-EBCDIC. This is planned
604 in the near future, however.
606 Whether an arbitrary piece of data will be treated as "characters" or
607 "bytes" by internal operations cannot be divined at the current time.
609 Use of locales with utf8 may lead to odd results. Currently there is
610 some attempt to apply 8-bit locale info to characters in the range
611 0..255, but this is demonstrably incorrect for locales that use
612 characters above that range (when mapped into Unicode). It will also
613 tend to run slower. Avoidance of locales is strongly encouraged.
615 =head1 UNICODE REGULAR EXPRESSION SUPPORT LEVEL
617 The following list of Unicode regular expression support describes
618 feature by feature the Unicode support implemented in Perl as of Perl
619 5.8.0. The "Level N" and the section numbers refer to the Unicode
620 Technical Report 18, "Unicode Regular Expression Guidelines".
626 Level 1 - Basic Unicode Support
628 2.1 Hex Notation - done [1]
629 Named Notation - done [2]
630 2.2 Categories - done [3][4]
631 2.3 Subtraction - MISSING [5][6]
632 2.4 Simple Word Boundaries - done [7]
633 2.5 Simple Loose Matches - done [8]
634 2.6 End of Line - MISSING [9][10]
638 [ 3] . \p{Is...} \P{Is...}
639 [ 4] now scripts (see UTR#24 Script Names) in addition to blocks
641 [ 6] can use look-ahead to emulate subtraction (*)
642 [ 7] include Letters in word characters
643 [ 8] see UTR#21 Case Mappings: Perl implements 1:1 mappings
644 [ 9] see UTR#13 Unicode Newline Guidelines
645 [10] should do ^ and $ also on \x{85}, \x{2028} and \x{2029})
646 (should also affect <>, $., and script line numbers)
648 (*) You can mimic class subtraction using lookahead.
649 For example, what TR18 might write as
651 [{Greek}-[{UNASSIGNED}]]
653 in Perl can be written as:
655 (?!\p{UNASSIGNED})\p{GreekBlock}
656 (?=\p{ASSIGNED})\p{GreekBlock}
658 But in this particular example, you probably really want
662 which will match assigned characters known to be part of the Greek script.
664 In other words: the matched character must not be a non-assigned
665 character, but it must be in the block of modern Greek characters.
669 Level 2 - Extended Unicode Support
671 3.1 Surrogates - MISSING
672 3.2 Canonical Equivalents - MISSING [11][12]
673 3.3 Locale-Independent Graphemes - MISSING [13]
674 3.4 Locale-Independent Words - MISSING [14]
675 3.5 Locale-Independent Loose Matches - MISSING [15]
677 [11] see UTR#15 Unicode Normalization
678 [12] have Unicode::Normalize but not integrated to regexes
679 [13] have \X but at this level . should equal that
680 [14] need three classes, not just \w and \W
681 [15] see UTR#21 Case Mappings
685 Level 3 - Locale-Sensitive Support
687 4.1 Locale-Dependent Categories - MISSING
688 4.2 Locale-Dependent Graphemes - MISSING [16][17]
689 4.3 Locale-Dependent Words - MISSING
690 4.4 Locale-Dependent Loose Matches - MISSING
691 4.5 Locale-Dependent Ranges - MISSING
693 [16] see UTR#10 Unicode Collation Algorithms
694 [17] have Unicode::Collate but not integrated to regexes
698 =head2 Unicode Encodings
700 Unicode characters are assigned to I<code points> which are abstract
701 numbers. To use these numbers various encodings are needed.
707 UTF-8 is the encoding used internally by Perl. UTF-8 is a variable
708 length (1 to 6 bytes, current character allocations require 4 bytes),
709 byteorder independent encoding. For ASCII, UTF-8 is transparent
710 (and we really do mean 7-bit ASCII, not any 8-bit encoding).
712 The following table is from Unicode 3.1.
714 Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte
716 U+0000..U+007F 00..7F
717 U+0080..U+07FF C2..DF 80..BF
718 U+0800..U+0FFF E0 A0..BF 80..BF
719 U+1000..U+FFFF E1..EF 80..BF 80..BF
720 U+10000..U+3FFFF F0 90..BF 80..BF 80..BF
721 U+40000..U+FFFFF F1..F3 80..BF 80..BF 80..BF
722 U+100000..U+10FFFF F4 80..8F 80..BF 80..BF
724 Or, another way to look at it, as bits:
726 Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte
729 00000bbbbbaaaaaa 110bbbbb 10aaaaaa
730 ccccbbbbbbaaaaaa 1110cccc 10bbbbbb 10aaaaaa
731 00000dddccccccbbbbbbaaaaaa 11110ddd 10cccccc 10bbbbbb 10aaaaaa
733 As you can see, the continuation bytes all begin with C<10>, and the
734 leading bits of the start byte tells how many bytes the are in the
739 Like UTF-8, but EBDCIC-safe, as UTF-8 is ASCII-safe.
741 =item UTF-16, UTF-16BE, UTF16-LE, Surrogates, and BOMs (Byte Order Marks)
743 (The followings items are mostly for reference, Perl doesn't
744 use them internally.)
746 UTF-16 is a 2 or 4 byte encoding. The Unicode code points
747 0x0000..0xFFFF are stored in two 16-bit units, and the code points
748 0x010000..0x10FFFF in two 16-bit units. The latter case is
749 using I<surrogates>, the first 16-bit unit being the I<high
750 surrogate>, and the second being the I<low surrogate>.
752 Surrogates are code points set aside to encode the 0x01000..0x10FFFF
753 range of Unicode code points in pairs of 16-bit units. The I<high
754 surrogates> are the range 0xD800..0xDBFF, and the I<low surrogates>
755 are the range 0xDC00..0xDFFFF. The surrogate encoding is
757 $hi = ($uni - 0x10000) / 0x400 + 0xD800;
758 $lo = ($uni - 0x10000) % 0x400 + 0xDC00;
762 $uni = 0x10000 + ($hi - 0xD8000) * 0x400 + ($lo - 0xDC00);
764 If you try to generate surrogates (for example by using chr()), you
765 will get an error because firstly a surrogate on its own is meaningless,
766 and secondly because Perl encodes its Unicode characters in UTF-8
767 (not 16-bit numbers), which makes the encoded character doubly illegal.
769 Because of the 16-bitness, UTF-16 is byteorder dependent. UTF-16
770 itself can be used for in-memory computations, but if storage or
771 transfer is required, either UTF-16BE (Big Endian) or UTF-16LE
772 (Little Endian) must be chosen.
774 This introduces another problem: what if you just know that your data
775 is UTF-16, but you don't know which endianness? Byte Order Marks
776 (BOMs) are a solution to this. A special character has been reserved
777 in Unicode to function as a byte order marker: the character with the
778 code point 0xFEFF is the BOM.
780 The trick is that if you read a BOM, you will know the byte order,
781 since if it was written on a big endian platform, you will read the
782 bytes 0xFE 0xFF, but if it was written on a little endian platform,
783 you will read the bytes 0xFF 0xFE. (And if the originating platform
784 was writing in UTF-8, you will read the bytes 0xEF 0xBB 0xBF.)
786 The way this trick works is that the character with the code point
787 0xFFFE is guaranteed not to be a valid Unicode character, so the
788 sequence of bytes 0xFF 0xFE is unambiguously "BOM, represented in
789 little-endian format" and cannot be "0xFFFE, represented in big-endian
792 =item UTF-32, UTF-32BE, UTF32-LE
794 The UTF-32 family is pretty much like the UTF-16 family, expect that
795 the units are 32-bit, and therefore the surrogate scheme is not
796 needed. The BOM signatures will be 0x00 0x00 0xFE 0xFF for BE and
797 0xFF 0xFE 0x00 0x00 for LE.
801 Encodings defined by the ISO 10646 standard. UCS-2 is a 16-bit
802 encoding, UCS-4 is a 32-bit encoding. Unlike UTF-16, UCS-2
803 is not extensible beyond 0xFFFF, because it does not use surrogates.
807 A seven-bit safe (non-eight-bit) encoding, useful if the
808 transport/storage is not eight-bit safe. Defined by RFC 2152.
812 =head2 Security Implications of Malformed UTF-8
814 Unfortunately, the specification of UTF-8 leaves some room for
815 interpretation of how many bytes of encoded output one should generate
816 from one input Unicode character. Strictly speaking, one is supposed
817 to always generate the shortest possible sequence of UTF-8 bytes,
818 because otherwise there is potential for input buffer overflow at the
819 receiving end of a UTF-8 connection. Perl always generates the shortest
820 length UTF-8, and with warnings on (C<-w> or C<use warnings;>) Perl will
821 warn about non-shortest length UTF-8 (and other malformations, too,
822 such as the surrogates, which are not real character code points.)
824 =head2 Unicode in Perl on EBCDIC
826 The way Unicode is handled on EBCDIC platforms is still rather
827 experimental. On such a platform, references to UTF-8 encoding in this
828 document and elsewhere should be read as meaning UTF-EBCDIC as
829 specified in Unicode Technical Report 16 unless ASCII vs EBCDIC issues
830 are specifically discussed. There is no C<utfebcdic> pragma or
831 ":utfebcdic" layer, rather, "utf8" and ":utf8" are re-used to mean
832 the platform's "natural" 8-bit encoding of Unicode. See L<perlebcdic>
833 for more discussion of the issues.
835 =head2 Using Unicode in XS
837 If you want to handle Perl Unicode in XS extensions, you may find
838 the following C APIs useful:
844 DO_UTF8(sv) returns true if the UTF8 flag is on and the bytes
845 pragma is not in effect. SvUTF8(sv) returns true is the UTF8
846 flag is on, the bytes pragma is ignored. Remember that UTF8
847 flag being on does not mean that there would be any characters
848 of code points greater than 255 or 127 in the scalar, or that
849 there even are any characters in the scalar. The UTF8 flag
850 means that any characters added to the string will be encoded
851 in UTF8 if the code points of the characters are greater than
852 255. Not "if greater than 127", since Perl's Unicode model
853 is not to use UTF-8 until it's really necessary.
857 uvuni_to_utf8(buf, chr) writes a Unicode character code point into a
858 buffer encoding the code point as UTF-8, and returns a pointer
859 pointing after the UTF-8 bytes.
863 utf8_to_uvuni(buf, lenp) reads UTF-8 encoded bytes from a buffer and
864 returns the Unicode character code point (and optionally the length of
865 the UTF-8 byte sequence).
869 utf8_length(s, len) returns the length of the UTF-8 encoded buffer in
870 characters. sv_len_utf8(sv) returns the length of the UTF-8 encoded
875 sv_utf8_upgrade(sv) converts the string of the scalar to its UTF-8
876 encoded form. sv_utf8_downgrade(sv) does the opposite (if possible).
877 sv_utf8_encode(sv) is like sv_utf8_upgrade but the UTF8 flag does not
878 get turned on. sv_utf8_decode() does the opposite of sv_utf8_encode().
882 is_utf8_char(buf) returns true if the buffer points to valid UTF-8.
886 is_utf8_string(buf, len) returns true if the len bytes of the buffer
891 UTF8SKIP(buf) will return the number of bytes in the UTF-8 encoded
892 character in the buffer. UNISKIP(chr) will return the number of bytes
893 required to UTF-8-encode the Unicode character code point.
897 utf8_distance(a, b) will tell the distance in characters between the
898 two pointers pointing to the same UTF-8 encoded buffer.
902 utf8_hop(s, off) will return a pointer to an UTF-8 encoded buffer that
903 is C<off> (positive or negative) Unicode characters displaced from the
908 pv_uni_display(dsv, spv, len, pvlim, flags) and sv_uni_display(dsv,
909 ssv, pvlim, flags) are useful for debug output of Unicode strings and
910 scalars (only for debug: they display B<all> characters as hexadecimal
915 ibcmp_utf8(s1, u1, len1, s2, u2, len2) can be used to compare two
916 strings case-insensitively in Unicode. (For case-sensitive
917 comparisons you can just use memEQ() and memNE() as usual.)
921 For more information, see L<perlapi>, and F<utf8.c> and F<utf8.h>
922 in the Perl source code distribution.
926 L<perluniintro>, L<encoding>, L<Encode>, L<open>, L<utf8>, L<bytes>,
927 L<perlretut>, L<perlvar/"${^WIDE_SYSTEM_CALLS}">
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