# QBitArray Class

The QBitArray class provides an array of bits. More...

Header: | #include <QBitArray> |

qmake: | QT += core |

**Note:** All functions in this class are reentrant.

## Public Functions

QBitArray() | |

QBitArray(int size, bool value = false) | |

QBitArray(const QBitArray &other) | |

QBitArray(QBitArray &&other) | |

bool | at(int i) const |

const char * | bits() const |

void | clear() |

void | clearBit(int i) |

int | count() const |

int | count(bool on) const |

bool | fill(bool value, int size = ...) |

void | fill(bool value, int begin, int end) |

bool | isEmpty() const |

bool | isNull() const |

void | resize(int size) |

void | setBit(int i) |

void | setBit(int i, bool value) |

int | size() const |

void | swap(QBitArray &other) |

bool | testBit(int i) const |

bool | toggleBit(int i) |

void | truncate(int pos) |

bool | operator!=(const QBitArray &other) const |

QBitArray & | operator&=(const QBitArray &other) |

QBitArray & | operator=(const QBitArray &other) |

QBitArray & | operator=(QBitArray &&other) |

bool | operator==(const QBitArray &other) const |

QBitRef | operator[](int i) |

bool | operator[](int i) const |

QBitRef | operator[](uint i) |

bool | operator[](uint i) const |

QBitArray & | operator^=(const QBitArray &other) |

QBitArray & | operator|=(const QBitArray &other) |

QBitArray | operator~() const |

## Static Public Members

QBitArray | fromBits(const char *data, qsizetype size) |

## Related Non-Members

QBitArray | operator&(const QBitArray &a1, const QBitArray &a2) |

QDataStream & | operator<<(QDataStream &out, const QBitArray &ba) |

QDataStream & | operator>>(QDataStream &in, QBitArray &ba) |

QBitArray | operator^(const QBitArray &a1, const QBitArray &a2) |

QBitArray | operator|(const QBitArray &a1, const QBitArray &a2) |

## Detailed Description

The QBitArray class provides an array of bits.

A QBitArray is an array that gives access to individual bits and provides operators (AND, OR, XOR, and NOT) that work on entire arrays of bits. It uses implicit sharing (copy-on-write) to reduce memory usage and to avoid the needless copying of data.

The following code constructs a QBitArray containing 200 bits initialized to false (0):

QBitArray ba(200);

To initialize the bits to true, either pass `true`

as second argument to the constructor, or call fill() later on.

QBitArray uses 0-based indexes, just like C++ arrays. To access the bit at a particular index position, you can use operator[](). On non-const bit arrays, operator[]() returns a reference to a bit that can be used on the left side of an assignment. For example:

QBitArray ba; ba.resize(3); ba[0] = true; ba[1] = false; ba[2] = true;

For technical reasons, it is more efficient to use testBit() and setBit() to access bits in the array than operator[](). For example:

QBitArray ba(3); ba.setBit(0, true); ba.setBit(1, false); ba.setBit(2, true);

QBitArray supports `&`

(AND), `|`

(OR), `^`

(XOR), `~`

(NOT), as well as `&=`

, `|=`

, and `^=`

. These operators work in the same way as the built-in C++ bitwise operators of the same name. For example:

QBitArray x(5); x.setBit(3, true); // x: [ 0, 0, 0, 1, 0 ] QBitArray y(5); y.setBit(4, true); // y: [ 0, 0, 0, 0, 1 ] x |= y; // x: [ 0, 0, 0, 1, 1 ]

For historical reasons, QBitArray distinguishes between a null bit array and an empty bit array. A *null* bit array is a bit array that is initialized using QBitArray's default constructor. An *empty* bit array is any bit array with size 0. A null bit array is always empty, but an empty bit array isn't necessarily null:

QBitArray().isNull(); // returns true QBitArray().isEmpty(); // returns true QBitArray(0).isNull(); // returns false QBitArray(0).isEmpty(); // returns true QBitArray(3).isNull(); // returns false QBitArray(3).isEmpty(); // returns false

All functions except isNull() treat null bit arrays the same as empty bit arrays; for example, QBitArray() compares equal to QBitArray(0). We recommend that you always use isEmpty() and avoid isNull().

**See also **QByteArray and QVector.

## Member Function Documentation

### QBitArray::QBitArray()

Constructs an empty bit array.

**See also **isEmpty().

### QBitArray::QBitArray(int *size*, bool *value* = false)

Constructs a bit array containing *size* bits. The bits are initialized with *value*, which defaults to false (0).

### QBitArray::QBitArray(const QBitArray &*other*)

Constructs a copy of *other*.

This operation takes constant time, because QBitArray is implicitly shared. This makes returning a QBitArray from a function very fast. If a shared instance is modified, it will be copied (copy-on-write), and that takes linear time.

**See also **operator=().

### QBitArray::QBitArray(QBitArray &&*other*)

Move-constructs a QBitArray instance, making it point at the same object that *other* was pointing to.

This function was introduced in Qt 5.2.

### bool QBitArray::at(int *i*) const

Returns the value of the bit at index position *i*.

*i* must be a valid index position in the bit array (i.e., 0 <= *i* < size()).

**See also **operator[]().

### const char *QBitArray::bits() const

Returns a pointer to a dense bit array for this QBitArray. Bits are counted upwards from the least significant bit in each byte. The the number of bits relevant in the last byte is given by `size() % 8`

.

This function was introduced in Qt 5.11.

**See also **fromBits() and size().

### void QBitArray::clear()

Clears the contents of the bit array and makes it empty.

**See also **resize() and isEmpty().

### void QBitArray::clearBit(int *i*)

Sets the bit at index position *i* to 0.

*i* must be a valid index position in the bit array (i.e., 0 <= *i* < size()).

**See also **setBit() and toggleBit().

### int QBitArray::count() const

Same as size().

### int QBitArray::count(bool *on*) const

If *on* is true, this function returns the number of 1-bits stored in the bit array; otherwise the number of 0-bits is returned.

### bool QBitArray::fill(bool *value*, int *size* = ...)

Sets every bit in the bit array to *value*, returning true if successful; otherwise returns `false`

. If *size* is different from -1 (the default), the bit array is resized to *size* beforehand.

Example:

QBitArray ba(8); ba.fill(true); // ba: [ 1, 1, 1, 1, 1, 1, 1, 1 ] ba.fill(false, 2); // ba: [ 0, 0 ]

**See also **resize().

### void QBitArray::fill(bool *value*, int *begin*, int *end*)

This is an overloaded function.

Sets bits at index positions *begin* up to (but not including) *end* to *value*.

*begin* must be a valid index position in the bit array (0 <= *begin* < size()).

*end* must be either a valid index position or equal to size(), in which case the fill operation runs until the end of the array (0 <= *end* <= size()).

Example:

QBitArray ba(4); ba.fill(true, 1, 2); // ba: [ 0, 1, 0, 0 ] ba.fill(true, 1, 3); // ba: [ 0, 1, 1, 0 ] ba.fill(true, 1, 4); // ba: [ 0, 1, 1, 1 ]

`[static] `

QBitArray QBitArray::fromBits(const char **data*, qsizetype *size*)

Creates a QBitArray with the dense bit array located at *data*, with *size* bits. The byte array at *data* must be at least *size* / 8 (rounded up) bytes long.

If *size* is not a multiple of 8, this function will include the lowest *size* % 8 bits from the last byte in *data*.

This function was introduced in Qt 5.11.

**See also **bits().

### bool QBitArray::isEmpty() const

Returns `true`

if this bit array has size 0; otherwise returns false.

**See also **size().

### bool QBitArray::isNull() const

Returns `true`

if this bit array is null; otherwise returns `false`

.

Example:

QBitArray().isNull(); // returns true QBitArray(0).isNull(); // returns false QBitArray(3).isNull(); // returns false

Qt makes a distinction between null bit arrays and empty bit arrays for historical reasons. For most applications, what matters is whether or not a bit array contains any data, and this can be determined using isEmpty().

**See also **isEmpty().

### void QBitArray::resize(int *size*)

Resizes the bit array to *size* bits.

If *size* is greater than the current size, the bit array is extended to make it *size* bits with the extra bits added to the end. The new bits are initialized to false (0).

If *size* is less than the current size, bits are removed from the end.

**See also **size().

### void QBitArray::setBit(int *i*)

Sets the bit at index position *i* to 1.

*i* must be a valid index position in the bit array (i.e., 0 <= *i* < size()).

**See also **clearBit() and toggleBit().

### void QBitArray::setBit(int *i*, bool *value*)

This is an overloaded function.

Sets the bit at index position *i* to *value*.

### int QBitArray::size() const

Returns the number of bits stored in the bit array.

**See also **resize().

### void QBitArray::swap(QBitArray &*other*)

Swaps bit array *other* with this bit array. This operation is very fast and never fails.

This function was introduced in Qt 4.8.

### bool QBitArray::testBit(int *i*) const

Returns `true`

if the bit at index position *i* is 1; otherwise returns `false`

.

*i* must be a valid index position in the bit array (i.e., 0 <= *i* < size()).

**See also **setBit() and clearBit().

### bool QBitArray::toggleBit(int *i*)

Inverts the value of the bit at index position *i*, returning the previous value of that bit as either true (if it was set) or false (if it was unset).

If the previous value was 0, the new value will be 1. If the previous value was 1, the new value will be 0.

*i* must be a valid index position in the bit array (i.e., 0 <= *i* < size()).

**See also **setBit() and clearBit().

### void QBitArray::truncate(int *pos*)

Truncates the bit array at index position *pos*.

If *pos* is beyond the end of the array, nothing happens.

**See also **resize().

### bool QBitArray::operator!=(const QBitArray &*other*) const

Returns `true`

if *other* is not equal to this bit array; otherwise returns `false`

.

**See also **operator==().

### QBitArray &QBitArray::operator&=(const QBitArray &*other*)

Performs the AND operation between all bits in this bit array and *other*. Assigns the result to this bit array, and returns a reference to it.

The result has the length of the longest of the two bit arrays, with any missing bits (if one array is shorter than the other) taken to be 0.

Example:

QBitArray a(3); QBitArray b(2); a[0] = 1; a[1] = 0; a[2] = 1; // a: [ 1, 0, 1 ] b[0] = 1; b[1] = 1; // b: [ 1, 1 ] a &= b; // a: [ 1, 0, 0 ]

**See also **operator&(), operator|=(), operator^=(), and operator~().

### QBitArray &QBitArray::operator=(const QBitArray &*other*)

Assigns *other* to this bit array and returns a reference to this bit array.

### QBitArray &QBitArray::operator=(QBitArray &&*other*)

Moves *other* to this bit array and returns a reference to this bit array.

This function was introduced in Qt 5.2.

### bool QBitArray::operator==(const QBitArray &*other*) const

Returns `true`

if *other* is equal to this bit array; otherwise returns `false`

.

**See also **operator!=().

### QBitRef QBitArray::operator[](int *i*)

Returns the bit at index position *i* as a modifiable reference.

*i* must be a valid index position in the bit array (i.e., 0 <= *i* < size()).

Example:

QBitArray a(3); a[0] = false; a[1] = true; a[2] = a[0] ^ a[1];

The return value is of type QBitRef, a helper class for QBitArray. When you get an object of type QBitRef, you can assign to it, and the assignment will apply to the bit in the QBitArray from which you got the reference.

The functions testBit(), setBit(), and clearBit() are slightly faster.

**See also **at(), testBit(), setBit(), and clearBit().

### bool QBitArray::operator[](int *i*) const

This is an overloaded function.

### QBitRef QBitArray::operator[](uint *i*)

This is an overloaded function.

### bool QBitArray::operator[](uint *i*) const

This is an overloaded function.

### QBitArray &QBitArray::operator^=(const QBitArray &*other*)

Performs the XOR operation between all bits in this bit array and *other*. Assigns the result to this bit array, and returns a reference to it.

The result has the length of the longest of the two bit arrays, with any missing bits (if one array is shorter than the other) taken to be 0.

Example:

QBitArray a(3); QBitArray b(2); a[0] = 1; a[1] = 0; a[2] = 1; // a: [ 1, 0, 1 ] b[0] = 1; b[1] = 1; // b: [ 1, 1 ] a ^= b; // a: [ 0, 1, 1 ]

**See also **operator^(), operator&=(), operator|=(), and operator~().

### QBitArray &QBitArray::operator|=(const QBitArray &*other*)

Performs the OR operation between all bits in this bit array and *other*. Assigns the result to this bit array, and returns a reference to it.

The result has the length of the longest of the two bit arrays, with any missing bits (if one array is shorter than the other) taken to be 0.

Example:

QBitArray a(3); QBitArray b(2); a[0] = 1; a[1] = 0; a[2] = 1; // a: [ 1, 0, 1 ] b[0] = 1; b[1] = 1; // b: [ 1, 1 ] a |= b; // a: [ 1, 1, 1 ]

**See also **operator|(), operator&=(), operator^=(), and operator~().

### QBitArray QBitArray::operator~() const

Returns a bit array that contains the inverted bits of this bit array.

Example:

## Related Non-Members

### QBitArray operator&(const QBitArray &*a1*, const QBitArray &*a2*)

Returns a bit array that is the AND of the bit arrays *a1* and *a2*.

Example:

QBitArray a(3); QBitArray b(2); QBitArray c; a[0] = 1; a[1] = 0; a[2] = 1; // a: [ 1, 0, 1 ] b[0] = 1; b[1] = 1; // b: [ 1, 1 ] c = a & b; // c: [ 1, 0, 0 ]

**See also **operator&=(), operator|(), and operator^().

### QDataStream &operator<<(QDataStream &*out*, const QBitArray &*ba*)

Writes bit array *ba* to stream *out*.

**See also **Format of the QDataStream operators.

### QDataStream &operator>>(QDataStream &*in*, QBitArray &*ba*)

Reads a bit array into *ba* from stream *in*.

**See also **Format of the QDataStream operators.

### QBitArray operator^(const QBitArray &*a1*, const QBitArray &*a2*)

Returns a bit array that is the XOR of the bit arrays *a1* and *a2*.

Example:

QBitArray a(3); QBitArray b(2); QBitArray c; a[0] = 1; a[1] = 0; a[2] = 1; // a: [ 1, 0, 1 ] b[0] = 1; b[1] = 1; // b: [ 1, 1 ] c = a ^ b; // c: [ 0, 1, 1 ]

**See also **operator^=(), operator&(), and operator|().

### QBitArray operator|(const QBitArray &*a1*, const QBitArray &*a2*)

Returns a bit array that is the OR of the bit arrays *a1* and *a2*.

Example:

QBitArray a(3); QBitArray b(2); QBitArray c; a[0] = 1; a[1] = 0; a[2] = 1; // a: [ 1, 0, 1 ] b[0] = 1; b[1] = 1; // b: [ 1, 1 ] c = a | b; // c: [ 1, 1, 1 ]

**See also **QBitArray::operator|=(), operator&(), and operator^().

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