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# QBitArray Class Reference

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

All the functions in this class are reentrant when Qt is built with thread support.

`#include <qbitarray.h>`

Inherits QByteArray.

List of all member functions.

## Public Members

- QBitArray ()
- QBitArray ( uint size )
- QBitArray ( const QBitArray & a )
- QBitArray & operator= ( const QBitArray & a )
- uint size () const
- bool resize ( uint size )
- bool fill ( bool v, int size = -1 )
- virtual void detach ()
- QBitArray copy () const
- bool testBit ( uint index ) const
- void setBit ( uint index )
- void setBit ( uint index, bool value )
- void clearBit ( uint index )
- bool toggleBit ( uint index )
- bool at ( uint index ) const
- QBitVal operator[] ( int index )
- bool operator[] ( int index ) const
- QBitArray & operator&= ( const QBitArray & a )
- QBitArray & operator|= ( const QBitArray & a )
- QBitArray & operator^= ( const QBitArray & a )
- QBitArray operator~ () const

## Related Functions

- QBitArray operator& ( const QBitArray & a1, const QBitArray & a2 )
- QBitArray operator| ( const QBitArray & a1, const QBitArray & a2 )
- QBitArray operator^ ( const QBitArray & a1, const QBitArray & a2 )
- QDataStream & operator<< ( QDataStream & s, const QBitArray & a )
- QDataStream & operator>> ( QDataStream & s, QBitArray & a )

## Detailed Description

The QBitArray class provides an array of bits.

Because QBitArray is a QMemArray, it uses explicit sharing with a reference count.

A QBitArray is a special byte array that can access individual bits and perform bit-operations (AND, OR, XOR and NOT) on entire arrays or bits.

Bits can be manipulated by the setBit() and clearBit() functions, but it is also possible to use the indexing [] operator to test and set individual bits. The [] operator is a little slower than setBit() and clearBit() because some tricks are required to implement single-bit assignments.

Example:

        QBitArray a(3);
        a.setBit( 0 );
        a.clearBit( 1 );
        a.setBit( 2 );     // a = [1 0 1]

        QBitArray b(3);
        b[0] = 1;
        b[1] = 1;
        b[2] = 0;          // b = [1 1 0]

        QBitArray c;
        c = ~a & b;        // c = [0 1 0]

When a QBitArray is constructed the bits are uninitialized. Use fill() to set all the bits to 0 or 1. The array can be resized with resize() and copied with copy(). Bits can be set with setBit() and cleared with clearBit(). Bits can be toggled with toggleBit(). A bit's value can be obtained with testBit() and with at().

QBitArray supports the & (AND), | (OR), ^ (XOR) and ~ (NOT) operators.

See also Collection Classes, Implicitly and Explicitly Shared Classes, and Non-GUI Classes.

## Member Function Documentation

### QBitArray::QBitArray ()

Constructs an empty bit array.

### QBitArray::QBitArray ( uint size )

Constructs a bit array of size bits. The bits are uninitialized.

See also fill().

### QBitArray::QBitArray ( const QBitArray & a )

Constructs a shallow copy of a.

### bool QBitArray::at ( uint index ) const

Returns the value (0 or 1) of the bit at position index.

See also operator[]().

### void QBitArray::clearBit ( uint index )

Clears the bit at position index, i.e. sets it to 0.

See also setBit() and toggleBit().

### QBitArray QBitArray::copy () const

Returns a deep copy of the bit array.

See also detach().

### void QBitArray::detach ()`[virtual]`

Detaches from shared bit array data and makes sure that this bit array is the only one referring to the data.

If multiple bit arrays share common data, this bit array dereferences the data and gets a copy of the data. Nothing happens if there is only a single reference.

See also copy().

Reimplemented from QMemArray.

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

Fills the bit array with v (1's if v is TRUE, or 0's if v is FALSE).

fill() resizes the bit array to size bits if size is nonnegative.

Returns FALSE if a nonnegative size was specified and the bit array could not be resized; otherwise returns TRUE.

See also resize().

### QBitArray & QBitArray::operator&= ( const QBitArray & a )

Performs the AND operation between all bits in this bit array and a. Returns a reference to this bit array.

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

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

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

### QBitArray & QBitArray::operator= ( const QBitArray & a )

Assigns a shallow copy of a to this bit array and returns a reference to this array.

### QBitVal QBitArray::operator[] ( int index )

Implements the [] operator for bit arrays.

The returned QBitVal is a context object. It makes it possible to get and set a single bit value by its index position.

Example:

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

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

See also at().

### bool QBitArray::operator[] ( int index ) const

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

Implements the [] operator for constant bit arrays.

### QBitArray & QBitArray::operator^= ( const QBitArray & a )

Performs the XOR operation between all bits in this bit array and a. Returns a reference to this bit array.

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

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

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

### QBitArray & QBitArray::operator|= ( const QBitArray & a )

Performs the OR operation between all bits in this bit array and a. Returns a reference to this bit array.

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

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

See also 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 ), b;
        a[0] = 1;  a[1] = 0; a[2] = 1;      // a = [1 0 1]
        b = ~a;                             // b = [0 1 0]

### bool QBitArray::resize ( uint size )

Resizes the bit array to size bits and returns TRUE if the bit array could be resized; otherwise returns FALSE. The array becomes a null array if size == 0.

If the array is expanded, the new bits are set to 0.

See also size().

### void QBitArray::setBit ( uint index, bool value )

Sets the bit at position index to value.

Equivalent to:

        if ( value )
            setBit( index );
        else
            clearBit( index );

See also clearBit() and toggleBit().

### void QBitArray::setBit ( uint index )

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

Sets the bit at position index to 1.

See also clearBit() and toggleBit().

### uint QBitArray::size () const

Returns the bit array's size (number of bits).

See also resize().

### bool QBitArray::testBit ( uint index ) const

Returns TRUE if the bit at position index is set, i.e. is 1; otherwise returns FALSE.

See also setBit() and clearBit().

### bool QBitArray::toggleBit ( uint index )

Toggles the bit at position index.

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

See also setBit() and clearBit().

## Related Functions

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

Returns the AND result between the bit arrays a1 and a2.

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

See also QBitArray::operator&=().

### QDataStream & operator<< ( QDataStream & s, const QBitArray & a )

Writes bit array a to stream s.

See also Format of the QDataStream operators.

### QDataStream & operator>> ( QDataStream & s, QBitArray & a )

Reads a bit array into a from stream s.

See also Format of the QDataStream operators.

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

Returns the XOR result between the bit arrays a1 and a2.

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

See also QBitArray::operator^().

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

Returns the OR result between the bit arrays a1 and a2.

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

See also QBitArray::operator|=().

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