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CollationKey Class Reference

Collation keys are generated by the Collator class. More...

#include <sortkey.h>


Public Member Functions

 CollationKey ()
 This creates an empty collation key based on the null string.
 CollationKey (const uint8_t *values, int32_t count)
 Creates a collation key based on the collation key values.
 CollationKey (const CollationKey &other)
 Copy constructor.
 ~CollationKey ()
 Sort key destructor.
const CollationKeyoperator= (const CollationKey &other)
 Assignment operator .
UBool operator== (const CollationKey &source) const
 Compare if two collation keys are the same.
UBool operator!= (const CollationKey &source) const
 Compare if two collation keys are not the same.
UBool isBogus (void) const
 Test to see if the key is in an invalid state.
const uint8_t * getByteArray (int32_t &count) const
 Returns a pointer to the collation key values.
uint8_t * toByteArray (int32_t &count) const
 Extracts the collation key values into a new array.
Collator::EComparisonResult compareTo (const CollationKey &target) const
 Convenience method which does a string(bit-wise) comparison of the two collation keys.
int32_t hashCode (void) const
 Creates an integer that is unique to the collation key.

Friends

class RuleBasedCollator


Detailed Description

Collation keys are generated by the Collator class.

Use the CollationKey objects instead of Collator to compare strings multiple times. A CollationKey preprocesses the comparison information from the Collator object to make the comparison faster. If you are not going to comparing strings multiple times, then using the Collator object is generally faster, since it only processes as much of the string as needed to make a comparison.

For example (with strength == tertiary)

When comparing "Abernathy" to "Baggins-Smythworthy", Collator only needs to process a couple of characters, while a comparison with CollationKeys will process all of the characters. On the other hand, if you are doing a sort of a number of fields, it is much faster to use CollationKeys, since you will be comparing strings multiple times.

Typical use of CollationKeys are in databases, where you store a CollationKey in a hidden field, and use it for sorting or indexing.

Example of use:

 
     UErrorCode success = U_ZERO_ERROR;
     Collator* myCollator = Collator::createInstance(success);
     CollationKey* keys = new CollationKey [3];
     myCollator->getCollationKey("Tom", keys[0], success );
     myCollator->getCollationKey("Dick", keys[1], success );
     myCollator->getCollationKey("Harry", keys[2], success );

     // Inside body of sort routine, compare keys this way:
     CollationKey tmp;
     if(keys[0].compareTo( keys[1] ) > 0 ) {
         tmp = keys[0]; keys[0] = keys[1]; keys[1] = tmp;
     }
     //...

Because Collator::compare()'s algorithm is complex, it is faster to sort long lists of words by retrieving collation keys with Collator::getCollationKey(). You can then cache the collation keys and compare them using CollationKey::compareTo().

Note: Collators with different Locale, CollationStrength and DecompositionMode settings will return different CollationKeys 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 different CollationKeys for same strings.

See also:
Collator

RuleBasedCollator

Version:
1.3 12/18/96
Author:
Helena Shih


Constructor & Destructor Documentation

CollationKey::CollationKey  ) 
 

This creates an empty collation key based on the null string.

An empty collation key contains no sorting information. When comparing two empty collation keys, the result is Collator::EQUAL. Comparing empty collation key with non-empty collation key is always Collator::LESS.

CollationKey::CollationKey const uint8_t *  values,
int32_t  count
 

Creates a collation key based on the collation key values.

Parameters:
values the collation key values
count number of collation key values, including trailing nulls.
See also:
#createBits

CollationKey::CollationKey const CollationKey other  ) 
 

Copy constructor.

CollationKey::~CollationKey  ) 
 

Sort key destructor.


Member Function Documentation

Collator::EComparisonResult CollationKey::compareTo const CollationKey target  )  const
 

Convenience method which does a string(bit-wise) comparison of the two collation keys.

Parameters:
sourceKey source collation key
targetKey target collation key
Returns:
Returns Collator::LESS if sourceKey < targetKey, Collator::GREATER if sourceKey > targetKey and Collator::EQUAL otherwise.

const uint8_t * CollationKey::getByteArray int32_t &  count  )  const [inline]
 

Returns a pointer to the collation key values.

The storage is owned by the collation key and the pointer will become invalid if the key is deleted.

Parameters:
count the output parameter of number of collation key values, including any trailing nulls.

int32_t CollationKey::hashCode void   )  const
 

Creates an integer that is unique to the collation key.

NOTE: this is not the same as String.hashCode.

Example of use:

 .    UErrorCode status = U_ZERO_ERROR;
 .    Collator *myCollation = Collator::createInstance(Locale::US, status);
 .    if (U_FAILURE(status)) return;
 .    CollationKey key1, key2;
 .    UErrorCode status1 = U_ZERO_ERROR, status2 = U_ZERO_ERROR;
 .    myCollation->getCollationKey("abc", key1, status1);
 .    if (U_FAILURE(status1)) { delete myCollation; return; }
 .    myCollation->getCollationKey("ABC", key2, status2);
 .    if (U_FAILURE(status2)) { delete myCollation; return; }
 .    // key1.hashCode() != key2.hashCode()
 
Returns:
the hash value based on the string's collation order.
See also:
UnicodeString::hashCode

UBool CollationKey::isBogus void   )  const [inline]
 

Test to see if the key is in an invalid state.

The key will be in an invalid state if it couldn't allocate memory for some operation.

Returns:
Returns TRUE if the key is in an invalid, FALSE otherwise.

UBool CollationKey::operator!= const CollationKey source  )  const [inline]
 

Compare if two collation keys are not the same.

Parameters:
source the collation key to compare to.
Returns:
Returns TRUE if two collation keys are different, FALSE otherwise.

UBool CollationKey::operator== const CollationKey source  )  const
 

Compare if two collation keys are the same.

Parameters:
source the collation key to compare to.
Returns:
Returns true if two collation keys are equal, false otherwise.

uint8_t* CollationKey::toByteArray int32_t &  count  )  const
 

Extracts the collation key values into a new array.

The caller owns this storage and should free it.

Parameters:
count the output parameter of number of collation key values, including any trailing nulls.
Deprecated:
Remove after 2003-mar-25. Use getByteArray instead.


The documentation for this class was generated from the following file:
Generated on Sat Jan 22 03:19:46 2005 for ICU 2.1 by  doxygen 1.4.0