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CollationKey Class Reference

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

#include <sortkey.h>


Public Methods

 CollationKey ()
 This creates an empty collation key based on the null string. More...

 CollationKey (const uint8_t *values, int32_t count)
 Creates a collation key based on the collation key values. More...

 CollationKey (const CollationKey &other)
 Copy constructor. More...

 ~CollationKey ()
 Sort key destructor. More...

const CollationKey & operator= (const CollationKey &other)
 Assignment operator @stable.

UBool operator== (const CollationKey &source) const
 Compare if two collation keys are the same. More...

UBool operator!= (const CollationKey &source) const
 Compare if two collation keys are not the same. More...

UBool isBogus (void) const
 Test to see if the key is in an invalid state. More...

const uint8_t * getByteArray (int32_t &count) const
 Returns a pointer to the collation key values. More...

uint8_t * toByteArray (int32_t &count) const
 Extracts the collation key values into a new array. More...

Collator::EComparisonResult compareTo (const CollationKey &target) const
 Convenience method which does a string(bit-wise) comparison of the two collation keys. More...

int32_t hashCode (void) const
 Creates an integer that is unique to the collation key. More...


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. @stable

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 @stable

CollationKey::CollationKey const CollationKey &    other
 

Copy constructor.

@stable

CollationKey::~CollationKey  
 

Sort key destructor.

@stable


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. @stable

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. @stable

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 @stable

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. @stable

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. @stable

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. @stable

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. @stable


The documentation for this class was generated from the following file:
Generated on Mon Mar 4 21:29:28 2002 for ICU 2.0 by doxygen1.2.14 written by Dimitri van Heesch, © 1997-2002