- Qt 5.15
- Qt Core
- C++ Classes
- QTextBoundaryFinder
- Qt 5.15.18 Reference Documentation

# QTextBoundaryFinder Class

The QTextBoundaryFinder class provides a way of finding Unicode text boundaries in a string. More...

Header: | #include <QTextBoundaryFinder>
qmake: | QT += core
Since: | Qt 4.4

This class was introduced in Qt 4.4.

- List of all members, including inherited members

Note: All functions in this class are reentrant.

## Public Types

enum | BoundaryReason { NotAtBoundary, BreakOpportunity, StartOfItem, EndOfItem, MandatoryBreak, SoftHyphen }
flags | BoundaryReasons
enum | BoundaryType { Grapheme, Word, Line, Sentence }

## Public Functions

| QTextBoundaryFinder(BoundaryType type, const QChar *chars, int length, unsigned char *buffer = nullptr, int bufferSize = 0)
| QTextBoundaryFinder(BoundaryType type, const QString &string)
| QTextBoundaryFinder(const QTextBoundaryFinder &other)
| QTextBoundaryFinder()
QTextBoundaryFinder & | operator=(const QTextBoundaryFinder &other)
| ~QTextBoundaryFinder()
BoundaryReasons | boundaryReasons() const
bool | isAtBoundary() const
bool | isValid() const
int | position() const
void | setPosition(int position)
QString | string() const
void | toEnd()
int | toNextBoundary()
int | toPreviousBoundary()
void | toStart()
BoundaryType | type() const

## Detailed Description

QTextBoundaryFinder allows to find Unicode text boundaries in a string, accordingly to the Unicode text boundary specification (see Unicode Standard Annex #14 and Unicode Standard Annex #29).

QTextBoundaryFinder can operate on a QString in four possible modes depending on the value of BoundaryType.

Units of Unicode characters that make up what the user thinks of as a character or basic unit of the language are here called Grapheme clusters. The two unicode characters 'A' + diaeresis do for example form one grapheme cluster as the user thinks of them as one character, yet it is in this case represented by two unicode code points (see https://www.unicode.org/reports/tr29/#Grapheme_Cluster_Boundaries).

Word boundaries are there to locate the start and end of what a language considers to be a word (see https://www.unicode.org/reports/tr29/#Word_Boundaries).

Line break boundaries give possible places where a line break might happen and sentence boundaries will show the beginning and end of whole sentences (see https://www.unicode.org/reports/tr29/#Sentence_Boundaries and https://www.unicode.org/reports/tr14/).

The first position in a string is always a valid boundary and refers to the position before the first character. The last position at the length of the string is also valid and refers to the position after the last character.

## Member Type Documentation

### enum QTextBoundaryFinder::BoundaryReason
flags QTextBoundaryFinder::BoundaryReasons

Constant | Value | Description
--- | --- | ---
`QTextBoundaryFinder::NotAtBoundary` | `0` | The boundary finder is not at a boundary position.
`QTextBoundaryFinder::BreakOpportunity` | `0x1f` | The boundary finder is at a break opportunity position. Such a break opportunity might also be an item boundary (either StartOfItem, EndOfItem, or combination of both), a mandatory line break, or a soft hyphen.
`QTextBoundaryFinder::StartOfItem` | `0x20` | Since 5.0. The boundary finder is at the start of a grapheme, a word, a sentence, or a line.
`QTextBoundaryFinder::EndOfItem` | `0x40` | Since 5.0. The boundary finder is at the end of a grapheme, a word, a sentence, or a line.
`QTextBoundaryFinder::MandatoryBreak` | `0x80` | Since 5.0. The boundary finder is at the end of line (can occur for a Line boundary type only).
`QTextBoundaryFinder::SoftHyphen` | `0x100` | The boundary finder is at the soft hyphen (can occur for a Line boundary type only).

The BoundaryReasons type is a typedef for QFlags<BoundaryReason>. It stores an OR combination of BoundaryReason values.

### enum QTextBoundaryFinder::BoundaryType

Constant | Value | Description
--- | --- | ---
`QTextBoundaryFinder::Grapheme` | `0` | Finds a grapheme which is the smallest boundary. It including letters, punctuation marks, numerals and more.
`QTextBoundaryFinder::Word` | `1` | Finds a word.
`QTextBoundaryFinder::Line` | `3` | Finds possible positions for breaking the text into multiple lines.
`QTextBoundaryFinder::Sentence` | `2` | Finds sentence boundaries. These include periods, question marks etc.

## Member Function Documentation

### QTextBoundaryFinder::QTextBoundaryFinder(BoundaryType type, const QChar *chars, int length, unsigned char *buffer = nullptr, int bufferSize = 0)

Creates a QTextBoundaryFinder object of type operating on chars with length.

buffer is an optional working buffer of size bufferSize you can pass to the QTextBoundaryFinder. If the buffer is large enough to hold the working data required (bufferSize >= length + 1), it will use this instead of allocating its own buffer.

Warning: QTextBoundaryFinder does not create a copy of chars. It is the application programmer's responsibility to ensure the array is allocated for as long as the QTextBoundaryFinder object stays alive. The same applies to buffer.

### QTextBoundaryFinder::QTextBoundaryFinder(BoundaryType type, const QString &string)

Creates a QTextBoundaryFinder object of type operating on string.

### QTextBoundaryFinder::QTextBoundaryFinder(const QTextBoundaryFinder &other)

Copies the QTextBoundaryFinder object, other.

### QTextBoundaryFinder::QTextBoundaryFinder()

Constructs an invalid QTextBoundaryFinder object.

### QTextBoundaryFinder &QTextBoundaryFinder::operator=(const QTextBoundaryFinder &other)

Assigns the object, other, to another QTextBoundaryFinder object.

### QTextBoundaryFinder::~QTextBoundaryFinder()

Destructs the QTextBoundaryFinder object.

### BoundaryReasons QTextBoundaryFinder::boundaryReasons() const

Returns the reasons for the boundary finder to have chosen the current position as a boundary.

### bool QTextBoundaryFinder::isAtBoundary() const

Returns `true` if the object's position() is currently at a valid text boundary.

### bool QTextBoundaryFinder::isValid() const

Returns `true` if the text boundary finder is valid; otherwise returns `false`. A default QTextBoundaryFinder is invalid.

### int QTextBoundaryFinder::position() const

Returns the current position of the QTextBoundaryFinder.

The range is from 0 (the beginning of the string) to the length of the string inclusive.

See also setPosition().

### void QTextBoundaryFinder::setPosition(int position)

Sets the current position of the QTextBoundaryFinder to position.

If position is out of bounds, it will be bound to only valid positions. In this case, valid positions are from 0 to the length of the string inclusive.

See also position().

### QString QTextBoundaryFinder::string() const

Returns the string the QTextBoundaryFinder object operates on.

### void QTextBoundaryFinder::toEnd()

Moves the finder to the end of the string. This is equivalent to setPosition(string.length()).

See also setPosition() and position().

### int QTextBoundaryFinder::toNextBoundary()

Moves the QTextBoundaryFinder to the next boundary position and returns that position.

Returns -1 if there is no next boundary.

### int QTextBoundaryFinder::toPreviousBoundary()

Moves the QTextBoundaryFinder to the previous boundary position and returns that position.

Returns -1 if there is no previous boundary.

### void QTextBoundaryFinder::toStart()

Moves the finder to the start of the string. This is equivalent to setPosition(0).

See also setPosition() and position().

### BoundaryType QTextBoundaryFinder::type() const

Returns the type of the QTextBoundaryFinder.