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unorm.h File Reference


Detailed Description

C API: Unicode Normalization.

Unicode normalization API

Note: This API has been replaced by the unorm2.h API and is only available for backward compatibility. The functions here simply delegate to the unorm2.h functions, for example unorm2_getInstance() and unorm2_normalize(). There is one exception: The new API does not provide a replacement for unorm_compare().

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://source.icu-project.org/repos/icu/icuhtml/trunk/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.

#include "unicode/utypes.h"
#include "unicode/uiter.h"
#include "unicode/unorm2.h"

Go to the source code of this file.

Defines

#define U_COMPARE_CODE_POINT_ORDER   0x8000
#define U_COMPARE_IGNORE_CASE   0x10000
#define UNORM_COMPARE_NORM_OPTIONS_SHIFT   20
#define UNORM_INPUT_IS_FCD   0x20000

Enumerations

enum  { UNORM_UNICODE_3_2 = 0x20 }
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
}

Functions

U_STABLE int32_t U_EXPORT2 unorm_compare (const UChar *s1, int32_t length1, const UChar *s2, int32_t length2, uint32_t options, UErrorCode *pErrorCode)
U_STABLE int32_t U_EXPORT2 unorm_concatenate (const UChar *left, int32_t leftLength, const UChar *right, int32_t rightLength, UChar *dest, int32_t destCapacity, UNormalizationMode mode, int32_t options, UErrorCode *pErrorCode)
U_STABLE UBool U_EXPORT2 unorm_isNormalized (const UChar *src, int32_t srcLength, UNormalizationMode mode, UErrorCode *pErrorCode)
U_STABLE UBool U_EXPORT2 unorm_isNormalizedWithOptions (const UChar *src, int32_t srcLength, UNormalizationMode mode, int32_t options, UErrorCode *pErrorCode)
U_STABLE int32_t U_EXPORT2 unorm_next (UCharIterator *src, UChar *dest, int32_t destCapacity, UNormalizationMode mode, int32_t options, UBool doNormalize, UBool *pNeededToNormalize, UErrorCode *pErrorCode)
U_STABLE int32_t U_EXPORT2 unorm_normalize (const UChar *source, int32_t sourceLength, UNormalizationMode mode, int32_t options, UChar *result, int32_t resultLength, UErrorCode *status)
U_STABLE int32_t U_EXPORT2 unorm_previous (UCharIterator *src, UChar *dest, int32_t destCapacity, UNormalizationMode mode, int32_t options, UBool doNormalize, UBool *pNeededToNormalize, UErrorCode *pErrorCode)
U_STABLE
UNormalizationCheckResult
U_EXPORT2 
unorm_quickCheck (const UChar *source, int32_t sourcelength, UNormalizationMode mode, UErrorCode *status)
U_STABLE
UNormalizationCheckResult
U_EXPORT2 
unorm_quickCheckWithOptions (const UChar *src, int32_t srcLength, UNormalizationMode mode, int32_t options, UErrorCode *pErrorCode)


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