Characters can be accessed in two ways: as code units or as * code points. * Unicode code points are 21-bit integers and are the scalar values * of Unicode characters. ICU uses the type UChar32 for them. * Unicode code units are the storage units of a given * Unicode/UCS Transformation Format (a character encoding scheme). * With UTF-16, all code points can be represented with either one * or two code units ("surrogates"). * String storage is typically based on code units, while properties * of characters are typically determined using code point values. * Some processes may be designed to work with sequences of code units, * or it may be known that all characters that are important to an * algorithm can be represented with single code units. * Other processes will need to use the code point access functions.
* *ForwardCharacterIterator provides nextPostInc() to access
* a code unit and advance an internal position into the text object,
* similar to a return text[position++].
* It provides next32PostInc() to access a code point and advance an internal
* position.
next32PostInc() assumes that the current position is that of * the beginning of a code point, i.e., of its first code unit. * After next32PostInc(), this will be true again. * In general, access to code units and code points in the same * iteration loop should not be mixed. In UTF-16, if the current position * is on a second code unit (Low Surrogate), then only that code unit * is returned even by next32PostInc().
* *For iteration with either function, there are two ways to * check for the end of the iteration. When there are no more * characters in the text object: *
* void function1(ForwardCharacterIterator &it) {
* UChar32 c;
* while(it.hasNext()) {
* c=it.next32PostInc();
* // use c
* }
* }
*
* void function1(ForwardCharacterIterator &it) {
* UChar c;
* while((c=it.nextPostInc())!=ForwardCharacterIterator::DONE) {
* // use c
* }
* }
*
*/
class U_COMMON_API ForwardCharacterIterator {
public:
/**
* Value returned by most of ForwardCharacterIterator's functions
* when the iterator has reached the limits of its iteration. */
enum { DONE = 0xffff };
/**
* Destructor.
* @stable
*/
virtual ~ForwardCharacterIterator() {}
/**
* Returns true when both iterators refer to the same
* character in the same character-storage object.
* @stable
*/
virtual UBool operator==(const ForwardCharacterIterator& that) const = 0;
/**
* Returns true when the iterators refer to different
* text-storage objects, or to different characters in the
* same text-storage object.
* @stable
*/
inline UBool operator!=(const ForwardCharacterIterator& that) const;
/**
* Generates a hash code for this iterator.
* @stable
*/
virtual int32_t hashCode(void) const = 0;
/**
* Returns a UClassID for this ForwardCharacterIterator ("poor man's
* RTTI").Despite the fact that this function is public, * DO NOT CONSIDER IT PART OF CHARACTERITERATOR'S API! * @stable */ virtual UClassID getDynamicClassID(void) const = 0; /** * Gets the current code unit for returning and advances to the next code unit * in the iteration range * (toward endIndex()). If there are * no more code units to return, returns DONE. * @draft */ virtual UChar nextPostInc(void) = 0; /** * Gets the current code point for returning and advances to the next code point * in the iteration range * (toward endIndex()). If there are * no more code points to return, returns DONE. * @draft */ virtual UChar32 next32PostInc(void) = 0; /** * Returns FALSE if there are no more code units or code points * at or after the current position in the iteration range. * This is used with nextPostInc() or next32PostInc() in forward * iteration. */ virtual UBool hasNext() = 0; protected: ForwardCharacterIterator() {} ForwardCharacterIterator(const ForwardCharacterIterator&) {} ForwardCharacterIterator &operator=(const ForwardCharacterIterator&) { return *this; } }; /** * Abstract class that defines an API for iteration * on text objects. * This is an interface for forward and backward iteration * and random access into a text object. * *
The API provides backward compatibility to the Java and older ICU * CharacterIterator classes but extends them significantly: *
Examples for some of the new functions:
* * Forward iteration with hasNext(): * void forward1(CharacterIterator &it) { * UChar32 c; * for(it.setToStart(); it.hasNext();) { * c=it.next32PostInc(); * // use c * } * } * * Forward iteration more similar to loops with the old forward iteration, * showing a way to convert simple for() loops: * void forward2(CharacterIterator &it) { * UChar c; * for(c=it.firstPostInc(); c!=CharacterIterator::DONE; c=it.nextPostInc()) { * // use c * } * } * * Backward iteration with setToEnd() and hasPrevious(): * void backward1(CharacterIterator &it) { * UChar32 c; * for(it.setToEnd(); it.hasPrevious();) { * c=it.previous32(); * // use c * } * } * * Backward iteration with a more traditional for() loop: * void backward2(CharacterIterator &it) { * UChar c; * for(c=it.last(); c!=CharacterIterator::DONE; c=it.previous()) { * // use c * } * } * * Example for random access: * void random(CharacterIterator &it) { * // set to the third code point from the beginning * it.move32(3, CharacterIterator::kStart); * // get a code point from here without moving the position * UChar32 c=it.current32(); * // get the position * int32_t pos=it.getIndex(); * // get the previous code unit * UChar u=it.previous(); * // move back one more code unit * it.move(-1, CharacterIterator::kCurrent); * // set the position back to where it was * // and read the same code point c and move beyond it * it.setIndex(pos); * if(c!=it.next32PostInc()) { * exit(1); // CharacterIterator inconsistent * } * } * *Examples, especially for the old API:
* * Function processing characters, in this example simple output *
* void processChar( UChar c )
* {
* cout << " " << c;
* }
*
* Traverse the text from start to finish
*
* void traverseForward(CharacterIterator& iter)
* {
* for(UChar c = iter.first(); c != CharacterIterator.DONE; c = iter.next()) {
* processChar(c);
* }
* }
*
* Traverse the text backwards, from end to start
*
* void traverseBackward(CharacterIterator& iter)
* {
* for(UChar c = iter.last(); c != CharacterIterator.DONE; c = iter.previous()) {
* processChar(c);
* }
* }
*
* Traverse both forward and backward from a given position in the text.
* Calls to notBoundary() in this example represents some additional stopping criteria.
*
* void traverseOut(CharacterIterator& iter, UTextOffset pos)
* {
* UChar c;
* for (c = iter.setIndex(pos);
* c != CharacterIterator.DONE && (Unicode::isLetter(c) || Unicode::isDigit(c));
* c = iter.next()) {}
* UTextOffset end = iter.getIndex();
* for (c = iter.setIndex(pos);
* c != CharacterIterator.DONE && (Unicode::isLetter(c) || Unicode::isDigit(c));
* c = iter.previous()) {}
* UTextOffset start = iter.getIndex() + 1;
*
* cout << "start: " << start << " end: " << end << endl;
* for (c = iter.setIndex(start); iter.getIndex() < end; c = iter.next() ) {
* processChar(c);
* }
* }
*
* Creating a StringCharacterIterator and calling the test functions
*
* void CharacterIterator_Example( void )
* {
* cout << endl << "===== CharacterIterator_Example: =====" << endl;
* UnicodeString text("Ein kleiner Satz.");
* StringCharacterIterator iterator(text);
* cout << "----- traverseForward: -----------" << endl;
* traverseForward( iterator );
* cout << endl << endl << "----- traverseBackward: ----------" << endl;
* traverseBackward( iterator );
* cout << endl << endl << "----- traverseOut: ---------------" << endl;
* traverseOut( iterator, 7 );
* cout << endl << endl << "-----" << endl;
* }
*
*/
class U_COMMON_API CharacterIterator : public ForwardCharacterIterator {
public:
/**
* Origin enumeration for the move() and move32() functions.
*/
enum EOrigin { kStart, kCurrent, kEnd };
/**
* Returns a pointer to a new CharacterIterator of the same
* concrete class as this one, and referring to the same
* character in the same text-storage object as this one. The
* caller is responsible for deleting the new clone.
* @stable
*/
virtual CharacterIterator* clone(void) const = 0;
/**
* Sets the iterator to refer to the first code unit in its
* iteration range, and returns that code unit.
* This can be used to begin an iteration with next().
* @draft
*/
virtual UChar first(void) = 0;
/**
* Sets the iterator to refer to the first code unit in its
* iteration range, returns that code unit, and moves the position
* to the second code unit. This is an alternative to setToStart()
* for forward iteration with nextPostInc().
* @draft
*/
virtual UChar firstPostInc(void);
/**
* Sets the iterator to refer to the first code point in its
* iteration range, and returns that code unit,
* This can be used to begin an iteration with next32().
* Note that an iteration with next32PostInc(), beginning with,
* e.g., setToStart() or firstPostInc(), is more efficient.
* @draft
*/
virtual UChar32 first32(void) = 0;
/**
* Sets the iterator to refer to the first code point in its
* iteration range, returns that code point, and moves the position
* to the second code point. This is an alternative to setToStart()
* for forward iteration with next32PostInc().
* @draft
*/
virtual UChar32 first32PostInc(void);
/**
* Sets the iterator to refer to the first code unit or code point in its
* iteration range. This can be used to begin a forward
* iteration with nextPostInc() or next32PostInc().
* @return the start position of the iteration range
* @draft
*/
inline UTextOffset setToStart();
/**
* Sets the iterator to refer to the last code unit in its
* iteration range, and returns that code unit.
* This can be used to begin an iteration with previous().
* @draft
*/
virtual UChar last(void) = 0;
/**
* Sets the iterator to refer to the last code point in its
* iteration range, and returns that code unit.
* This can be used to begin an iteration with previous32().
* @draft
*/
virtual UChar32 last32(void) = 0;
/**
* Sets the iterator to the end of its iteration range, just behind
* the last code unit or code point. This can be used to begin a backward
* iteration with previous() or previous32().
* @return the end position of the iteration range
* @draft
*/
inline UTextOffset setToEnd();
/**
* Sets the iterator to refer to the "position"-th code unit
* in the text-storage object the iterator refers to, and
* returns that code unit.
* @draft
*/
virtual UChar setIndex(UTextOffset position) = 0;
/**
* Sets the iterator to refer to the beginning of the code point
* that contains the "position"-th code unit
* in the text-storage object the iterator refers to, and
* returns that code point.
* The current position is adjusted to the beginning of the code point
* (its first code unit).
* @draft
*/
virtual UChar32 setIndex32(UTextOffset position) = 0;
/**
* Returns the code unit the iterator currently refers to.
* @draft
*/
virtual UChar current(void) const = 0;
/**
* Returns the code point the iterator currently refers to.
* @draft
*/
virtual UChar32 current32(void) const = 0;
/**
* Advances to the next code unit in the iteration range
* (toward endIndex()), and returns that code unit. If there are
* no more code units to return, returns DONE.
* @draft
*/
virtual UChar next(void) = 0;
/**
* Advances to the next code point in the iteration range
* (toward endIndex()), and returns that code point. If there are
* no more code points to return, returns DONE.
* Note that iteration with "pre-increment" semantics is less
* efficient than iteration with "post-increment" semantics
* that is provided by next32PostInc().
* @draft
*/
virtual UChar32 next32(void) = 0;
/**
* Advances to the previous code unit in the iteration rance
* (toward startIndex()), and returns that code unit. If there are
* no more code units to return, returns DONE.
* @draft
*/
virtual UChar previous(void) = 0;
/**
* Advances to the previous code point in the iteration rance
* (toward startIndex()), and returns that code point. If there are
* no more code points to return, returns DONE.
* @draft
*/
virtual UChar32 previous32(void) = 0;
/**
* Returns FALSE if there are no more code units or code points
* before the current position in the iteration range.
* This is used with previous() or previous32() in backward
* iteration.
*/
virtual UBool hasPrevious() = 0;
/**
* Returns the numeric index in the underlying text-storage
* object of the character returned by first(). Since it's
* possible to create an iterator that iterates across only
* part of a text-storage object, this number isn't
* necessarily 0.
* @stable
*/
inline UTextOffset startIndex(void) const;
/**
* Returns the numeric index in the underlying text-storage
* object of the position immediately BEYOND the character
* returned by last().
* @stable
*/
inline UTextOffset endIndex(void) const;
/**
* Returns the numeric index in the underlying text-storage
* object of the character the iterator currently refers to
* (i.e., the character returned by current()).
* @stable
*/
inline UTextOffset getIndex(void) const;
/**
* Returns the length of the entire text in the underlying
* text-storage object.
*/
inline int32_t getLength() const;
/**
* Moves the current position relative to the start or end of the
* iteration range, or relative to the current position itself.
* The movement is expressed in numbers of code units forward
* or backward by specifying a positive or negative delta.
* @return the new position
*/
virtual UTextOffset move(int32_t delta, EOrigin origin) = 0;
/**
* Moves the current position relative to the start or end of the
* iteration range, or relative to the current position itself.
* The movement is expressed in numbers of code points forward
* or backward by specifying a positive or negative delta.
* @return the new position
*/
virtual UTextOffset move32(int32_t delta, EOrigin origin) = 0;
/**
* Copies the text under iteration into the UnicodeString
* referred to by "result".
* @param result Receives a copy of the text under iteration.
* @stable
*/
virtual void getText(UnicodeString& result) = 0;
protected:
CharacterIterator() {}
CharacterIterator(int32_t length);
CharacterIterator(int32_t length, UTextOffset position);
CharacterIterator(int32_t length, UTextOffset begin, UTextOffset end, UTextOffset position);
CharacterIterator(const CharacterIterator &that);
CharacterIterator &operator=(const CharacterIterator &that);
int32_t textLength; // need this for correct getText() and hashCode()
UTextOffset pos;
UTextOffset begin;
UTextOffset end;
};
inline UBool
ForwardCharacterIterator::operator!=(const ForwardCharacterIterator& that) const {
return !operator==(that);
}
inline UTextOffset
CharacterIterator::setToStart() {
return move(0, kStart);
}
inline UTextOffset
CharacterIterator::setToEnd() {
return move(0, kEnd);
}
inline UTextOffset
CharacterIterator::startIndex(void) const {
return begin;
}
inline UTextOffset
CharacterIterator::endIndex(void) const {
return end;
}
inline UTextOffset
CharacterIterator::getIndex(void) const {
return pos;
}
inline int32_t
CharacterIterator::getLength(void) const {
return textLength;
}
#endif