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# QBitArray Class Reference

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

    #include <QBitArray>

Part of the QtCore module.

Note: All the functions in this class are reentrant.

- List of all members, including inherited members

### Public Functions

- QBitArray ()
- QBitArray ( int size, bool value = false )
- QBitArray ( const QBitArray & other )
- bool at ( int i ) const
- void clear ()
- void clearBit ( int i )
- int count () const
- bool fill ( bool value, int size = -1 )
- 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
- 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 )
- 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

### 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=().

### 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[]().

### 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().

### bool QBitArray::fill ( bool value, int size = -1 )

Sets every bit in the bit array to value. 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 member function, provided for convenience. It behaves essentially like the above function.

Sets bits at index positions begin up to and excluding end to value.

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

### 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 member function, provided for convenience. It behaves essentially like the above 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().

### 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.

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] = 0;             // 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.

### 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 member function, provided for convenience. It behaves essentially like the above function.

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

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

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

This is an overloaded member function, provided for convenience. It behaves essentially like the above 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] = 0;             // 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] = 0;             // 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:

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

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

## 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.

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

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

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

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

Writes bit array ba to stream out.

See also Format of the QDataStream operators.

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

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

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.

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

See also QBitArray::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.

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

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