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      1 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 
      5 #ifndef BASE_I18N_BREAK_ITERATOR_H_
      6 #define BASE_I18N_BREAK_ITERATOR_H_
      7 
      8 #include "base/basictypes.h"
      9 #include "base/i18n/base_i18n_export.h"
     10 #include "base/strings/string16.h"
     11 
     12 // The BreakIterator class iterates through the words, word breaks, and
     13 // line breaks in a UTF-16 string.
     14 //
     15 // It provides several modes, BREAK_WORD, BREAK_LINE, and BREAK_NEWLINE,
     16 // which modify how characters are aggregated into the returned string.
     17 //
     18 // Under BREAK_WORD mode, once a word is encountered any non-word
     19 // characters are not included in the returned string (e.g. in the
     20 // UTF-16 equivalent of the string " foo bar! ", the word breaks are at
     21 // the periods in ". .foo. .bar.!. .").
     22 // Note that Chinese/Japanese/Thai do not use spaces between words so that
     23 // boundaries can fall in the middle of a continuous run of non-space /
     24 // non-punctuation characters.
     25 //
     26 // Under BREAK_LINE mode, once a line breaking opportunity is encountered,
     27 // any non-word  characters are included in the returned string, breaking
     28 // only when a space-equivalent character or a line breaking opportunity
     29 // is encountered (e.g. in the UTF16-equivalent of the string " foo bar! ",
     30 // the breaks are at the periods in ". .foo .bar! .").
     31 //
     32 // Note that lines can be broken at any character/syllable/grapheme cluster
     33 // boundary in Chinese/Japanese/Korean and at word boundaries in Thai
     34 // (Thai does not use spaces between words). Therefore, this is NOT the same
     35 // as breaking only at space-equivalent characters where its former
     36 // name (BREAK_SPACE) implied.
     37 //
     38 // Under BREAK_NEWLINE mode, all characters are included in the returned
     39 // string, breking only when a newline-equivalent character is encountered
     40 // (eg. in the UTF-16 equivalent of the string "foo\nbar!\n\n", the line
     41 // breaks are at the periods in ".foo\n.bar\n.\n.").
     42 //
     43 // To extract the words from a string, move a BREAK_WORD BreakIterator
     44 // through the string and test whether IsWord() is true. E.g.,
     45 //   BreakIterator iter(str, BreakIterator::BREAK_WORD);
     46 //   if (!iter.Init())
     47 //     return false;
     48 //   while (iter.Advance()) {
     49 //     if (iter.IsWord()) {
     50 //       // Region [iter.prev(), iter.pos()) contains a word.
     51 //       VLOG(1) << "word: " << iter.GetString();
     52 //     }
     53 //   }
     54 
     55 namespace base {
     56 namespace i18n {
     57 
     58 class BASE_I18N_EXPORT BreakIterator {
     59  public:
     60   enum BreakType {
     61     BREAK_WORD,
     62     BREAK_LINE,
     63     // TODO(jshin): Remove this after reviewing call sites.
     64     // If call sites really need break only on space-like characters
     65     // implement it separately.
     66     BREAK_SPACE = BREAK_LINE,
     67     BREAK_NEWLINE,
     68     BREAK_CHARACTER,
     69   };
     70 
     71   // Requires |str| to live as long as the BreakIterator does.
     72   BreakIterator(const string16& str, BreakType break_type);
     73   ~BreakIterator();
     74 
     75   // Init() must be called before any of the iterators are valid.
     76   // Returns false if ICU failed to initialize.
     77   bool Init();
     78 
     79   // Advance to the next break.  Returns false if we've run past the end of
     80   // the string.  (Note that the very last "break" is after the final
     81   // character in the string, and when we advance to that position it's the
     82   // last time Advance() returns true.)
     83   bool Advance();
     84 
     85   // Under BREAK_WORD mode, returns true if the break we just hit is the
     86   // end of a word. (Otherwise, the break iterator just skipped over e.g.
     87   // whitespace or punctuation.)  Under BREAK_LINE and BREAK_NEWLINE modes,
     88   // this distinction doesn't apply and it always retuns false.
     89   bool IsWord() const;
     90 
     91   // Under BREAK_WORD mode, returns true if |position| is at the end of word or
     92   // at the start of word. It always retuns false under BREAK_LINE and
     93   // BREAK_NEWLINE modes.
     94   bool IsEndOfWord(size_t position) const;
     95   bool IsStartOfWord(size_t position) const;
     96 
     97   // Returns the string between prev() and pos().
     98   // Advance() must have been called successfully at least once for pos() to
     99   // have advanced to somewhere useful.
    100   string16 GetString() const;
    101 
    102   // Returns the value of pos() returned before Advance() was last called.
    103   size_t prev() const { return prev_; }
    104 
    105   // Returns the current break position within the string,
    106   // or BreakIterator::npos when done.
    107   size_t pos() const { return pos_; }
    108 
    109  private:
    110   // ICU iterator, avoiding ICU ubrk.h dependence.
    111   // This is actually an ICU UBreakiterator* type, which turns out to be
    112   // a typedef for a void* in the ICU headers. Using void* directly prevents
    113   // callers from needing access to the ICU public headers directory.
    114   void* iter_;
    115 
    116   // The string we're iterating over.
    117   const string16& string_;
    118 
    119   // The breaking style (word/space/newline).
    120   BreakType break_type_;
    121 
    122   // Previous and current iterator positions.
    123   size_t prev_, pos_;
    124 
    125   DISALLOW_COPY_AND_ASSIGN(BreakIterator);
    126 };
    127 
    128 }  // namespace i18n
    129 }  // namespace base
    130 
    131 #endif  // BASE_I18N_BREAK_ITERATOR_H_
    132