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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, breaking 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     // But don't remove this one!
70     RULE_BASED,
71   };
72 
73   // Requires |str| to live as long as the BreakIterator does.
74   BreakIterator(const string16& str, BreakType break_type);
75   // Make a rule-based iterator. BreakType == RULE_BASED is implied.
76   // TODO(andrewhayden): This signature could easily be misinterpreted as
77   // "(const string16& str, const string16& locale)". We should do something
78   // better.
79   BreakIterator(const string16& str, const string16& rules);
80   ~BreakIterator();
81 
82   // Init() must be called before any of the iterators are valid.
83   // Returns false if ICU failed to initialize.
84   bool Init();
85 
86   // Advance to the next break.  Returns false if we've run past the end of
87   // the string.  (Note that the very last "break" is after the final
88   // character in the string, and when we advance to that position it's the
89   // last time Advance() returns true.)
90   bool Advance();
91 
92   // Updates the text used by the iterator, resetting the iterator as if
93   // if Init() had been called again. Any old state is lost. Returns true
94   // unless there is an error setting the text.
95   bool SetText(const base::char16* text, const size_t length);
96 
97   // Under BREAK_WORD mode, returns true if the break we just hit is the
98   // end of a word. (Otherwise, the break iterator just skipped over e.g.
99   // whitespace or punctuation.)  Under BREAK_LINE and BREAK_NEWLINE modes,
100   // this distinction doesn't apply and it always returns false.
101   bool IsWord() const;
102 
103   // Under BREAK_WORD mode, returns true if |position| is at the end of word or
104   // at the start of word. It always returns false under BREAK_LINE and
105   // BREAK_NEWLINE modes.
106   bool IsEndOfWord(size_t position) const;
107   bool IsStartOfWord(size_t position) const;
108 
109   // Returns the string between prev() and pos().
110   // Advance() must have been called successfully at least once for pos() to
111   // have advanced to somewhere useful.
112   string16 GetString() const;
113 
114   // Returns the value of pos() returned before Advance() was last called.
prev()115   size_t prev() const { return prev_; }
116 
117   // Returns the current break position within the string,
118   // or BreakIterator::npos when done.
pos()119   size_t pos() const { return pos_; }
120 
121  private:
122   // ICU iterator, avoiding ICU ubrk.h dependence.
123   // This is actually an ICU UBreakiterator* type, which turns out to be
124   // a typedef for a void* in the ICU headers. Using void* directly prevents
125   // callers from needing access to the ICU public headers directory.
126   void* iter_;
127 
128   // The string we're iterating over. Can be changed with SetText(...)
129   const string16& string_;
130 
131   // Rules for our iterator. Mutually exclusive with break_type_.
132   const string16 rules_;
133 
134   // The breaking style (word/space/newline). Mutually exclusive with rules_
135   BreakType break_type_;
136 
137   // Previous and current iterator positions.
138   size_t prev_, pos_;
139 
140   DISALLOW_COPY_AND_ASSIGN(BreakIterator);
141 };
142 
143 }  // namespace i18n
144 }  // namespace base
145 
146 #endif  // BASE_I18N_BREAK_ITERATOR_H_
147