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# QBitArray Class Reference
[QtCore module]

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

### Methods

- __init__ (self)
- __init__ (self, int size, bool val = False)
- __init__ (self, QBitArray other)
- bool at (self, int i)
- clear (self)
- clearBit (self, int i)
- int count (self)
- int count (self, bool on)
- detach (self)
- fill (self, bool val, int first, int last)
- bool fill (self, bool aval, int asize = -1)
- bool isDetached (self)
- bool isEmpty (self)
- bool isNull (self)
- resize (self, int size)
- setBit (self, int i)
- setBit (self, int i, bool val)
- int size (self)
- bool testBit (self, int i)
- bool toggleBit (self, int i)
- truncate (self, int pos)

### Special Methods

- QBitArray __and__ (self, QBitArray)
- bool __eq__ (self, QBitArray a)
- bool __getitem__ (self, int i)
- long __hash__ (self)
- QBitArray __iand__ (self, QBitArray)
- QBitArray __invert__ (self)
- QBitArray __ior__ (self, QBitArray)
- QBitArray __ixor__ (self, QBitArray)
- bool __ne__ (self, QBitArray a)
- QBitArray __or__ (self, QBitArray)
- QBitArray __xor__ (self, QBitArray)

## 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.

## Method Documentation

### QBitArray.__init__ (self)

Constructs an empty bit array.

See also isEmpty().

### QBitArray.__init__ (self, int size, bool val = False)

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

### QBitArray.__init__ (self, 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 (self, int i)

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[]().

### QBitArray.clear (self)

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

See also resize() and isEmpty().

### QBitArray.clearBit (self, 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 (self)

Same as size().

### int QBitArray.count (self, bool on)

This is an overloaded member function, provided for convenience.

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.

### QBitArray.detach (self)

### QBitArray.fill (self, bool val, int first, int last)

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().

### bool QBitArray.fill (self, bool aval, int asize = -1)

This is an overloaded member function, provided for convenience.

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.isDetached (self)

### bool QBitArray.isEmpty (self)

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

See also size().

### bool QBitArray.isNull (self)

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().

### QBitArray.resize (self, 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().

### QBitArray.setBit (self, 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().

### QBitArray.setBit (self, int i, bool val)

This is an overloaded member function, provided for convenience.

Sets the bit at index position i to value.

### int QBitArray.size (self)

Returns the number of bits stored in the bit array.

See also resize().

### bool QBitArray.testBit (self, int i)

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 (self, 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().

### QBitArray.truncate (self, int pos)

Truncates the bit array at index position pos.

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

See also resize().

### QBitArray QBitArray.__and__ (self, QBitArray)

### bool QBitArray.__eq__ (self, QBitArray a)

### bool QBitArray.__getitem__ (self, int i)

### long QBitArray.__hash__ (self)

### QBitArray QBitArray.__iand__ (self, QBitArray)

### QBitArray QBitArray.__invert__ (self)

### QBitArray QBitArray.__ior__ (self, QBitArray)

### QBitArray QBitArray.__ixor__ (self, QBitArray)

### bool QBitArray.__ne__ (self, QBitArray a)

### QBitArray QBitArray.__or__ (self, QBitArray)

### QBitArray QBitArray.__xor__ (self, QBitArray)