// Copyright (c) 2011 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef BASE_I18N_BREAK_ITERATOR_H_
#define BASE_I18N_BREAK_ITERATOR_H_
#include "base/basictypes.h"
#include "base/i18n/base_i18n_export.h"
#include "base/strings/string16.h"
// The BreakIterator class iterates through the words, word breaks, and
// line breaks in a UTF-16 string.
//
// It provides several modes, BREAK_WORD, BREAK_LINE, and BREAK_NEWLINE,
// which modify how characters are aggregated into the returned string.
//
// Under BREAK_WORD mode, once a word is encountered any non-word
// characters are not included in the returned string (e.g. in the
// UTF-16 equivalent of the string " foo bar! ", the word breaks are at
// the periods in ". .foo. .bar.!. .").
// Note that Chinese/Japanese/Thai do not use spaces between words so that
// boundaries can fall in the middle of a continuous run of non-space /
// non-punctuation characters.
//
// Under BREAK_LINE mode, once a line breaking opportunity is encountered,
// any non-word characters are included in the returned string, breaking
// only when a space-equivalent character or a line breaking opportunity
// is encountered (e.g. in the UTF16-equivalent of the string " foo bar! ",
// the breaks are at the periods in ". .foo .bar! .").
//
// Note that lines can be broken at any character/syllable/grapheme cluster
// boundary in Chinese/Japanese/Korean and at word boundaries in Thai
// (Thai does not use spaces between words). Therefore, this is NOT the same
// as breaking only at space-equivalent characters where its former
// name (BREAK_SPACE) implied.
//
// Under BREAK_NEWLINE mode, all characters are included in the returned
// string, breaking only when a newline-equivalent character is encountered
// (eg. in the UTF-16 equivalent of the string "foo\nbar!\n\n", the line
// breaks are at the periods in ".foo\n.bar\n.\n.").
//
// To extract the words from a string, move a BREAK_WORD BreakIterator
// through the string and test whether IsWord() is true. E.g.,
// BreakIterator iter(str, BreakIterator::BREAK_WORD);
// if (!iter.Init())
// return false;
// while (iter.Advance()) {
// if (iter.IsWord()) {
// // Region [iter.prev(), iter.pos()) contains a word.
// VLOG(1) << "word: " << iter.GetString();
// }
// }
namespace base {
namespace i18n {
class BASE_I18N_EXPORT BreakIterator {
public:
enum BreakType {
BREAK_WORD,
BREAK_LINE,
// TODO(jshin): Remove this after reviewing call sites.
// If call sites really need break only on space-like characters
// implement it separately.
BREAK_SPACE = BREAK_LINE,
BREAK_NEWLINE,
BREAK_CHARACTER,
};
// Requires |str| to live as long as the BreakIterator does.
BreakIterator(const string16& str, BreakType break_type);
~BreakIterator();
// Init() must be called before any of the iterators are valid.
// Returns false if ICU failed to initialize.
bool Init();
// Advance to the next break. Returns false if we've run past the end of
// the string. (Note that the very last "break" is after the final
// character in the string, and when we advance to that position it's the
// last time Advance() returns true.)
bool Advance();
// Under BREAK_WORD mode, returns true if the break we just hit is the
// end of a word. (Otherwise, the break iterator just skipped over e.g.
// whitespace or punctuation.) Under BREAK_LINE and BREAK_NEWLINE modes,
// this distinction doesn't apply and it always returns false.
bool IsWord() const;
// Under BREAK_WORD mode, returns true if |position| is at the end of word or
// at the start of word. It always returns false under BREAK_LINE and
// BREAK_NEWLINE modes.
bool IsEndOfWord(size_t position) const;
bool IsStartOfWord(size_t position) const;
// Returns the string between prev() and pos().
// Advance() must have been called successfully at least once for pos() to
// have advanced to somewhere useful.
string16 GetString() const;
// Returns the value of pos() returned before Advance() was last called.
size_t prev() const { return prev_; }
// Returns the current break position within the string,
// or BreakIterator::npos when done.
size_t pos() const { return pos_; }
private:
// ICU iterator, avoiding ICU ubrk.h dependence.
// This is actually an ICU UBreakiterator* type, which turns out to be
// a typedef for a void* in the ICU headers. Using void* directly prevents
// callers from needing access to the ICU public headers directory.
void* iter_;
// The string we're iterating over.
const string16& string_;
// The breaking style (word/space/newline).
BreakType break_type_;
// Previous and current iterator positions.
size_t prev_, pos_;
DISALLOW_COPY_AND_ASSIGN(BreakIterator);
};
} // namespace i18n
} // namespace base
#endif // BASE_I18N_BREAK_ITERATOR_H_