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