#include "unicode/utypes.h"
Go to the source code of this file.
Defines | |
#define | u_normalize unorm_normalize |
The function u_normalize() has been renamed to unorm_normalize() for consistency. More... | |
Typedefs | |
typedef enum UNormalizationCheckResult | UNormalizationCheckResult |
Result values for unorm_quickCheck(). More... | |
Enumerations | |
enum | UNormalizationMode { UNORM_NONE = 1, UNORM_NFD = 2, UNORM_NFKD = 3, UNORM_NFC = 4, UNORM_DEFAULT = UNORM_NFC, UNORM_NFKC = 5, UNORM_FCD = 6, UNORM_MODE_COUNT, UCOL_NO_NORMALIZATION = 1, UCOL_DECOMP_CAN = 2, UCOL_DECOMP_COMPAT = 3, UCOL_DEFAULT_NORMALIZATION = UCOL_DECOMP_COMPAT, UCOL_DECOMP_CAN_COMP_COMPAT = 4, UCOL_DECOMP_COMPAT_COMP_CAN = 5, UCOL_IGNORE_HANGUL = 16, UNORM_IGNORE_HANGUL = 16 } |
Constants for normalization modes. More... | |
enum | UNormalizationCheckResult { UNORM_NO, UNORM_YES, UNORM_MAYBE } |
Result values for unorm_quickCheck(). More... | |
Functions | |
U_CAPI int32_t U_EXPORT2 | unorm_normalize (const UChar *source, int32_t sourceLength, UNormalizationMode mode, int32_t options, UChar *result, int32_t resultLength, UErrorCode *status) |
Normalize a string. More... | |
U_CAPI UNormalizationCheckResult U_EXPORT2 | unorm_quickCheck (const UChar *source, int32_t sourcelength, UNormalizationMode mode, UErrorCode *status) |
Performing quick check on a string, to quickly determine if the string is in a particular normalization format. More... |
unorm_normalize
transforms Unicode text into an equivalent composed or decomposed form, allowing for easier sorting and searching of text. unorm_normalize
supports the standard normalization forms described in Unicode Standard Annex #15 — Unicode Normalization Forms.
Characters with accents or other adornments can be encoded in several different ways in Unicode. For example, take the character A-acute. In Unicode, this can be encoded as a single character (the "composed" form):
00C1 LATIN CAPITAL LETTER A WITH ACUTE
or as two separate characters (the "decomposed" form):
0041 LATIN CAPITAL LETTER A 0301 COMBINING ACUTE ACCENT
To a user of your program, however, both of these sequences should be treated as the same "user-level" character "A with acute accent". When you are searching or comparing text, you must ensure that these two sequences are treated equivalently. In addition, you must handle characters with more than one accent. Sometimes the order of a character's combining accents is significant, while in other cases accent sequences in different orders are really equivalent.
Similarly, the string "ffi" can be encoded as three separate letters:
0066 LATIN SMALL LETTER F 0066 LATIN SMALL LETTER F 0069 LATIN SMALL LETTER I
or as the single character
FB03 LATIN SMALL LIGATURE FFI
The ffi ligature is not a distinct semantic character, and strictly speaking it shouldn't be in Unicode at all, but it was included for compatibility with existing character sets that already provided it. The Unicode standard identifies such characters by giving them "compatibility" decompositions into the corresponding semantic characters. When sorting and searching, you will often want to use these mappings.
unorm_normalize
helps solve these problems by transforming text into the canonical composed and decomposed forms as shown in the first example above. In addition, you can have it perform compatibility decompositions so that you can treat compatibility characters the same as their equivalents. Finally, unorm_normalize
rearranges accents into the proper canonical order, so that you do not have to worry about accent rearrangement on your own.
Form FCD, "Fast C or D", is also designed for collation. It allows to work on strings that are not necessarily normalized with an algorithm (like in collation) that works under "canonical closure", i.e., it treats precomposed characters and their decomposed equivalents the same.
It is not a normalization form because it does not provide for uniqueness of representation. Multiple strings may be canonically equivalent (their NFDs are identical) and may all conform to FCD without being identical themselves.
The form is defined such that the "raw decomposition", the recursive canonical decomposition of each character, results in a string that is canonically ordered. This means that precomposed characters are allowed for as long as their decompositions do not need canonical reordering.
Its advantage for a process like collation is that all NFD and most NFC texts - and many unnormalized texts - already conform to FCD and do not need to be normalized (NFD) for such a process. The FCD quick check will return UNORM_YES for most strings in practice.
unorm_normalize(UNORM_FCD) may be implemented with UNORM_NFD.
For more details on FCD see the collation design document: http://oss.software.ibm.com/cvs/icu/~checkout~/icuhtml/design/collation/ICU_collation_design.htm
ICU collation performs either NFD or FCD normalization automatically if normalization is turned on for the collator object. Beyond collation and string search, normalized strings may be useful for string equivalence comparisons, transliteration/transcription, unique representations, etc.
The W3C generally recommends to exchange texts in NFC. Note also that most legacy character encodings use only precomposed forms and often do not encode any combining marks by themselves. For conversion to such character encodings the Unicode text needs to be normalized to NFC. For more usage examples, see the Unicode Standard Annex.
Definition in file unorm.h.
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The function u_normalize() has been renamed to unorm_normalize() for consistency. The old name is deprecated.
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Result values for unorm_quickCheck(). For details see Unicode Technical Report 15.
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Result values for unorm_quickCheck(). For details see Unicode Technical Report 15.
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Normalize a string. The string will be normalized according the specified normalization mode and options (there are currently no options defined).
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Performing quick check on a string, to quickly determine if the string is in a particular normalization format. Three types of result can be returned UNORM_YES, UNORM_NO or UNORM_MAYBE. Result UNORM_YES indicates that the argument string is in the desired normalized format, UNORM_NO determines that argument string is not in the desired normalized format. A UNORM_MAYBE result indicates that a more thorough check is required, the user may have to put the string in its normalized form and compare the results.
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