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The QBitArray class provides an array of bits. More...
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().
Constructs an empty bit array.
See also isEmpty().
Constructs a bit array containing size bits. The bits are initialized with value, which defaults to false (0).
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=().
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[]().
Clears the contents of the bit array and makes it empty.
See also resize() and isEmpty().
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().
Same as size().
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.
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().
This is an overloaded 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()).
Returns true if this bit array has size 0; otherwise returns false.
See also size().
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().
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().
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().
This is an overloaded function.
Sets the bit at index position i to value.
Returns the number of bits stored in the bit array.
See also resize().
Swaps bit array other with this bit array. This operation is very fast and never fails.
This function was introduced in Qt 4.8.
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().
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().
Truncates the bit array at index position pos.
If pos is beyond the end of the array, nothing happens.
See also resize().
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