QBitArray Class

Detailed Description

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().