break_iterator.h revision 4e180b6a0b4720a9b8e9e959a882386f690f08ff
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 55namespace base { 56namespace i18n { 57 58class 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 returns 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 returns 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