icuSources/common/unicode/dbbi.h

   1 /*
   2 **********************************************************************
   3 *   Copyright (C) 1999-2004 IBM Corp. All rights reserved.
   4 **********************************************************************
   5 *   Date        Name        Description
   6 *   12/1/99    rgillam     Complete port from Java.
   7 *   01/13/2000 helena      Added UErrorCode to ctors.
   8 **********************************************************************
   9 */
  10
  11 #ifndef DBBI_H
  12 #define DBBI_H
  13
  14 #include "unicode/rbbi.h"
  15
  16 #if !UCONFIG_NO_BREAK_ITERATION
  17
  18 U_NAMESPACE_BEGIN
  19
  20 /* forward declaration */
  21 class DictionaryBasedBreakIteratorTables;
  22
  23 /**
  24  * A subclass of RuleBasedBreakIterator that adds the ability to use a dictionary
  25  * to further subdivide ranges of text beyond what is possible using just the
  26  * state-table-based algorithm.  This is necessary, for example, to handle
  27  * word and line breaking in Thai, which doesn't use spaces between words.  The
  28  * state-table-based algorithm used by RuleBasedBreakIterator is used to divide
  29  * up text as far as possible, and then contiguous ranges of letters are
  30  * repeatedly compared against a list of known words (i.e., the dictionary)
  31  * to divide them up into words.
  32  *
  33  * <p>Applications do not normally need to include this header.</p>
  34  *
  35  * <p>This class will probably be deprecated in a future release of ICU, and replaced
  36  *  with a more flexible and capable dictionary based break iterator.  This change
  37  *  should be invisible to applications, because creation and use of instances of
  38  *  DictionaryBasedBreakIterator is through the factories and abstract
  39  *  API on class BreakIterator, which will remain stable.</p>
  40  *
  41  * <p>This class is not intended to be subclassed.</p>
  42  *
  43  *
  44  * DictionaryBasedBreakIterator uses the same rule language as RuleBasedBreakIterator,
  45  * but adds one more special substitution name: &lt;dictionary&gt;.  This substitution
  46  * name is used to identify characters in words in the dictionary.  The idea is that
  47  * if the iterator passes over a chunk of text that includes two or more characters
  48  * in a row that are included in &lt;dictionary&gt;, it goes back through that range and
  49  * derives additional break positions (if possible) using the dictionary.
  50  *
  51  * DictionaryBasedBreakIterator is also constructed with the filename of a dictionary
  52  * file.  It follows a prescribed search path to locate the dictionary (right now,
  53  * it looks for it in /com/ibm/text/resources in each directory in the classpath,
  54  * and won't find it in JAR files, but this location is likely to change).  The
  55  * dictionary file is in a serialized binary format.  We have a very primitive (and
  56  * slow) BuildDictionaryFile utility for creating dictionary files, but aren't
  57  * currently making it public.  Contact us for help.
  58  * <p>
  59  * <b> NOTE </b>  The DictionaryBasedIterator class is still under development.  The
  60  * APIs are not in stable condition yet.
  61  */
  62 class U_COMMON_API DictionaryBasedBreakIterator : public RuleBasedBreakIterator {
  63
  64 private:
  65
  66     /**
  67      * when a range of characters is divided up using the dictionary, the break
  68      * positions that are discovered are stored here, preventing us from having
  69      * to use either the dictionary or the state table again until the iterator
  70      * leaves this range of text
  71      */
  72     int32_t* cachedBreakPositions;
  73
  74     /**
  75      * The number of elements in cachedBreakPositions
  76      */
  77     int32_t numCachedBreakPositions;
  78
  79     /**
  80      * if cachedBreakPositions is not null, this indicates which item in the
  81      * cache the current iteration position refers to
  82      */
  83     int32_t positionInCache;
  84
  85     DictionaryBasedBreakIteratorTables  *fTables;
  86
  87     /**=======================================================================
  88      * Create a dictionary based break boundary detection iterator.
  89      * @param tablesImage The location for the dictionary to be loaded into memory
  90      * @param dictionaryFilename The name of the dictionary file
  91      * @param status the error code status
  92      * @return A dictionary based break detection iterator.  The UErrorCode& status
  93      * parameter is used to return status information to the user.
  94      * To check whether the construction succeeded or not, you should check
  95      * the value of U_SUCCESS(err).  If you wish more detailed information, you
  96      * can check for informational error results which still indicate success.  For example,
  97      * U_FILE_ACCESS_ERROR will be returned if the file does not exist.
  98      * The caller owns the returned object and is responsible for deleting it.
  99      ======================================================================= */
 100     DictionaryBasedBreakIterator(UDataMemory* tablesImage, const char* dictionaryFilename, UErrorCode& status);
 101
 102 public:
 103     //=======================================================================
 104     // boilerplate
 105     //=======================================================================
 106
 107     /**
 108      * Destructor
 109      * @stable ICU 2.0
 110      */
 111     virtual ~DictionaryBasedBreakIterator();
 112
 113     /**
 114      * Default constructor.  Creates an "empty" break iterator.
 115      * Such an iterator can subsequently be assigned to.
 116      * @return the newly created DictionaryBaseBreakIterator.
 117      * @stable ICU 2.0
 118      */
 119      DictionaryBasedBreakIterator();
 120
 121      /**
 122       * Copy constructor.
 123       * @param other The DictionaryBasedBreakIterator to be copied.
 124       * @return the newly created DictionaryBasedBreakIterator.
 125       * @stable ICU 2.0
 126       */
 127      DictionaryBasedBreakIterator(const DictionaryBasedBreakIterator &other);
 128
 129     /**
 130      * Assignment operator.
 131      * @param that The object to be copied.
 132      * @return the newly set DictionaryBasedBreakIterator.
 133      * @stable ICU 2.0
 134      */
 135     DictionaryBasedBreakIterator& operator=(const DictionaryBasedBreakIterator& that);
 136
 137     /**
 138      * Returns a newly-constructed RuleBasedBreakIterator with the same
 139      * behavior, and iterating over the same text, as this one.
 140      * @return Returns a newly-constructed RuleBasedBreakIterator.
 141      * @stable ICU 2.0
 142      */
 143     virtual BreakIterator* clone(void) const;
 144
 145     //=======================================================================
 146     // BreakIterator overrides
 147     //=======================================================================
 148     /**
 149      * Advances the iterator backwards, to the last boundary preceding this one.
 150      * @return The position of the last boundary position preceding this one.
 151      * @stable ICU 2.0
 152      */
 153     virtual int32_t previous(void);
 154
 155     /**
 156      * Sets the iterator to refer to the first boundary position following
 157      * the specified position.
 158      * @param offset The position from which to begin searching for a break position.
 159      * @return The position of the first break after the current position.
 160      * @stable ICU 2.0
 161      */
 162     virtual int32_t following(int32_t offset);
 163
 164     /**
 165      * Sets the iterator to refer to the last boundary position before the
 166      * specified position.
 167      * @param offset The position to begin searching for a break from.
 168      * @return The position of the last boundary before the starting position.
 169      * @stable ICU 2.0
 170      */
 171     virtual int32_t preceding(int32_t offset);
 172
 173     /**
 174      * Returns the class ID for this class.  This is useful only for
 175      * comparing to a return value from getDynamicClassID().  For example:
 176      *
 177      *      Base* polymorphic_pointer = createPolymorphicObject();
 178      *      if (polymorphic_pointer->getDynamicClassID() ==
 179      *          Derived::getStaticClassID()) ...
 180      *
 181      * @return          The class ID for all objects of this class.
 182      * @stable ICU 2.0
 183      */
 184     static UClassID U_EXPORT2 getStaticClassID(void);
 185
 186     /**
 187      * Returns a unique class ID POLYMORPHICALLY.  Pure virtual override.
 188      * This method is to implement a simple version of RTTI, since not all
 189      * C++ compilers support genuine RTTI.  Polymorphic operator==() and
 190      * clone() methods call this method.
 191      *
 192      * @return          The class ID for this object. All objects of a
 193      *                  given class have the same class ID.  Objects of
 194      *                  other classes have different class IDs.
 195      * @stable ICU 2.0
 196      */
 197     virtual UClassID getDynamicClassID(void) const;
 198
 199 protected:
 200     //=======================================================================
 201     // implementation
 202     //=======================================================================
 203     /**
 204      * This method is the actual implementation of the next() method.  All iteration
 205      * vectors through here.  This method initializes the state machine to state 1
 206      * and advances through the text character by character until we reach the end
 207      * of the text or the state machine transitions to state 0.  We update our return
 208      * value every time the state machine passes through a possible end state.
 209      * @internal
 210      */
 211     virtual int32_t handleNext(void);
 212
 213     /**
 214      * removes the cache of break positions (usually in response to a change in
 215      * position of some sort)
 216      * @internal
 217      */
 218     virtual void reset(void);
 219
 220     /**
 221      *  init    Initialize a dbbi.  Common routine for use by constructors.
 222      *  @internal
 223      */
 224     void init();
 225
 226     /**
 227      * @param stackBuffer user allocated space for the new clone. If NULL new memory will be allocated.
 228      * If buffer is not large enough, new memory will be allocated.
 229      * @param BufferSize reference to size of allocated space.
 230      * If BufferSize == 0, a sufficient size for use in cloning will
 231      * be returned ('pre-flighting')
 232      * If BufferSize is not enough for a stack-based safe clone,
 233      * new memory will be allocated.
 234      * @param status to indicate whether the operation went on smoothly or there were errors
 235      *  An informational status value, U_SAFECLONE_ALLOCATED_ERROR, is used if any allocations were
 236      *  necessary.
 237      * @return pointer to the new clone
 238      * @internal
 239      */
 240     virtual BreakIterator *  createBufferClone(void *stackBuffer,
 241                                                int32_t &BufferSize,
 242                                                UErrorCode &status);
 243
 244
 245 private:
 246     /**
 247      * This is the function that actually implements the dictionary-based
 248      * algorithm.  Given the endpoints of a range of text, it uses the
 249      * dictionary to determine the positions of any boundaries in this
 250      * range.  It stores all the boundary positions it discovers in
 251      * cachedBreakPositions so that we only have to do this work once
 252      * for each time we enter the range.
 253      * @param startPos The start position of a range of text
 254      * @param endPos The end position of a range of text
 255      * @param status The error code status
 256      */
 257     void divideUpDictionaryRange(int32_t startPos, int32_t endPos, UErrorCode &status);
 258
 259
 260     /*
 261      * HSYS : Please revisit with Rich, the ctors of the DBBI class is currently
 262      * marked as private.
 263      */
 264     friend class DictionaryBasedBreakIteratorTables;
 265     friend class BreakIterator;
 266 };
 267
 268 U_NAMESPACE_END
 269
 270 #endif /* #if !UCONFIG_NO_BREAK_ITERATION */
 271
 272 #endif