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.
5 #ifndef BASE_I18N_BREAK_ITERATOR_H_
6 #define BASE_I18N_BREAK_ITERATOR_H_
10 #include "base/i18n/base_i18n_export.h"
11 #include "base/macros.h"
12 #include "base/strings/string16.h"
13 #include "base/strings/string_piece.h"
15 // The BreakIterator class iterates through the words, word breaks, and
16 // line breaks in a UTF-16 string.
18 // It provides several modes, BREAK_WORD, BREAK_LINE, and BREAK_NEWLINE,
19 // which modify how characters are aggregated into the returned string.
21 // Under BREAK_WORD mode, once a word is encountered any non-word
22 // characters are not included in the returned string (e.g. in the
23 // UTF-16 equivalent of the string " foo bar! ", the word breaks are at
24 // the periods in ". .foo. .bar.!. .").
25 // Note that Chinese/Japanese/Thai do not use spaces between words so that
26 // boundaries can fall in the middle of a continuous run of non-space /
27 // non-punctuation characters.
29 // Under BREAK_LINE mode, once a line breaking opportunity is encountered,
30 // any non-word characters are included in the returned string, breaking
31 // only when a space-equivalent character or a line breaking opportunity
32 // is encountered (e.g. in the UTF16-equivalent of the string " foo bar! ",
33 // the breaks are at the periods in ". .foo .bar! .").
35 // Note that lines can be broken at any character/syllable/grapheme cluster
36 // boundary in Chinese/Japanese/Korean and at word boundaries in Thai
37 // (Thai does not use spaces between words). Therefore, this is NOT the same
38 // as breaking only at space-equivalent characters where its former
39 // name (BREAK_SPACE) implied.
41 // Under BREAK_NEWLINE mode, all characters are included in the returned
42 // string, breaking only when a newline-equivalent character is encountered
43 // (eg. in the UTF-16 equivalent of the string "foo\nbar!\n\n", the line
44 // breaks are at the periods in ".foo\n.bar\n.\n.").
46 // To extract the words from a string, move a BREAK_WORD BreakIterator
47 // through the string and test whether IsWord() is true. E.g.,
48 // BreakIterator iter(str, BreakIterator::BREAK_WORD);
51 // while (iter.Advance()) {
52 // if (iter.IsWord()) {
53 // // Region [iter.prev(), iter.pos()) contains a word.
54 // VLOG(1) << "word: " << iter.GetString();
61 class BASE_I18N_EXPORT BreakIterator {
66 // TODO(jshin): Remove this after reviewing call sites.
67 // If call sites really need break only on space-like characters
68 // implement it separately.
69 BREAK_SPACE = BREAK_LINE,
72 // But don't remove this one!
76 enum WordBreakStatus {
77 // The end of text that the iterator recognizes as word characters.
78 // Non-word characters are things like punctuation and spaces.
80 // Characters that the iterator can skip past, such as punctuation,
81 // whitespace, and, if using RULE_BASED mode, characters from another
84 // Only used if not in BREAK_WORD or RULE_BASED mode. This is returned for
85 // newlines, line breaks, and character breaks.
89 // Requires |str| to live as long as the BreakIterator does.
90 BreakIterator(const StringPiece16& str, BreakType break_type);
91 // Make a rule-based iterator. BreakType == RULE_BASED is implied.
92 // TODO(andrewhayden): This signature could easily be misinterpreted as
93 // "(const string16& str, const string16& locale)". We should do something
95 BreakIterator(const StringPiece16& str, const string16& rules);
98 // Init() must be called before any of the iterators are valid.
99 // Returns false if ICU failed to initialize.
102 // Advance to the next break. Returns false if we've run past the end of
103 // the string. (Note that the very last "break" is after the final
104 // character in the string, and when we advance to that position it's the
105 // last time Advance() returns true.)
108 // Updates the text used by the iterator, resetting the iterator as if
109 // if Init() had been called again. Any old state is lost. Returns true
110 // unless there is an error setting the text.
111 bool SetText(const base::char16* text, const size_t length);
113 // Under BREAK_WORD mode, returns true if the break we just hit is the
114 // end of a word. (Otherwise, the break iterator just skipped over e.g.
115 // whitespace or punctuation.) Under BREAK_LINE and BREAK_NEWLINE modes,
116 // this distinction doesn't apply and it always returns false.
119 // Under BREAK_WORD mode:
120 // - Returns IS_SKIPPABLE_WORD if non-word characters, such as punctuation or
121 // spaces, are found.
122 // - Returns IS_WORD_BREAK if the break we just hit is the end of a sequence
123 // of word characters.
124 // Under RULE_BASED mode:
125 // - Returns IS_SKIPPABLE_WORD if characters outside the rules' character set
126 // or non-word characters, such as punctuation or spaces, are found.
127 // - Returns IS_WORD_BREAK if the break we just hit is the end of a sequence
128 // of word characters that are in the rules' character set.
129 // Not under BREAK_WORD or RULE_BASED mode:
130 // - Returns IS_LINE_OR_CHAR_BREAK.
131 BreakIterator::WordBreakStatus GetWordBreakStatus() const;
133 // Under BREAK_WORD mode, returns true if |position| is at the end of word or
134 // at the start of word. It always returns false under BREAK_LINE and
135 // BREAK_NEWLINE modes.
136 bool IsEndOfWord(size_t position) const;
137 bool IsStartOfWord(size_t position) const;
139 // Under BREAK_CHARACTER mode, returns whether |position| is a Unicode
140 // grapheme boundary.
141 bool IsGraphemeBoundary(size_t position) const;
143 // Returns the string between prev() and pos().
144 // Advance() must have been called successfully at least once for pos() to
145 // have advanced to somewhere useful.
146 string16 GetString() const;
148 StringPiece16 GetStringPiece() const;
150 // Returns the value of pos() returned before Advance() was last called.
151 size_t prev() const { return prev_; }
153 // Returns the current break position within the string,
154 // or BreakIterator::npos when done.
155 size_t pos() const { return pos_; }
158 // ICU iterator, avoiding ICU ubrk.h dependence.
159 // This is actually an ICU UBreakiterator* type, which turns out to be
160 // a typedef for a void* in the ICU headers. Using void* directly prevents
161 // callers from needing access to the ICU public headers directory.
164 // The string we're iterating over. Can be changed with SetText(...)
165 StringPiece16 string_;
167 // Rules for our iterator. Mutually exclusive with break_type_.
168 const string16 rules_;
170 // The breaking style (word/space/newline). Mutually exclusive with rules_
171 BreakType break_type_;
173 // Previous and current iterator positions.
176 DISALLOW_COPY_AND_ASSIGN(BreakIterator);
182 #endif // BASE_I18N_BREAK_ITERATOR_H_