The C API for Collator performs locale-sensitive
String
comparison
The C API for Collator performs locale-sensitiveString
comparison. You use this class to build searching and sorting routines for natural language text.Like other locale-sensitive classes, you can use the function
ucol_open()
, to obtain the appropriate pointer toUCollator
object for a given locale. If you need to understand the details of a particular collation strategy or if you need to modify that strategy.The following example shows how to compare two strings using the
UCollator
for the default locale.// Compare two strings in the default locale UErrorCode success = U_ZERO_ERROR; UCollator* myCollator = ucol_open(NULL, &success); UChar source[4], target[4]; u_uastrcpy(source, "abc"); u_uastrcpy(target, "ABC"); if( u_strcoll(myCollator, source, u_strlen(source), target, u_strlen(target)) == UCOL_LESS) { printf("abc is less than ABC\n"); }else{ printf("abc is greater than or equal to ABC\n"); }You can set a
Collator
's strength property to determine the level of difference considered significant in comparisons. Four strengths are provided:UCOL_PRIMARY
,UCOL_SECONDARY
,UCOL_TERTIARY
, andUCOL_IDENTICAL
. The exact assignment of strengths to language features is locale dependant. For example, in Czech, "e" and "f" are considered primary differences, while "e" and "\u00EA" are secondary differences, "e" and "E" are tertiary differences and "e" and "e" are identical. The following shows how both case and accents could be ignored for US English.//Get the Collator for US English and set its strength to UCOL_PRIMARY UErrorCode success = U_ZERO_ERROR; UCollator* usCollator = ucol_open("en_US", &success); ucol_setStrength(usCollator, UCOL_PRIMARY); UChar source[4], target[4]; u_uastrcpy(source, "abc"); u_uastrcpy(target, "ABC"); if( u_strcoll(myCollator, source, u_strlen(source), target, u_strlen(target)) == UCOL_EQUAL) { printf("'abc' and 'ABC' strings are equivalent with strength UCOL_PRIMARY\n"); }For comparing
String
s exactly once, theu_strcoll
method provides the best performance. When sorting a list ofString
s however, it is generally necessary to compare eachString
multiple times. In this case,sortKey
s provide better performance. Theucol_getsortKey
method converts aString
to a series of bits that can be compared bitwise against othersortKey
s usingmemcmp()
Note:
UCollator
s with different Locale, Collation Strength and Decomposition Mode settings will return different sort orders for the same set of strings. Locales have specific collation rules, and the way in which secondary and tertiary differences are taken into account, for example, will result in a different sorting order for same strings.
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