base/i18n/break_iterator.h

   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/string16.h"
  10 #include "base/i18n/base_i18n_export.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_