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C# BitArray Examples

Use the BitArray class and its constructor to reduce memory usage.
BitArray is a compact and easy-to-use object. Found in System.Collections, it offers a clear interface to bitwise operations. It allows you to perform bitwise operations. With it we count and display bits.BitConverter
First, BitArray has many constructors, including ones that receive int32, int32 arrays, byte arrays and default values. When you pass values to the constructor, integers are copied, but bytes and bools are processed first.

Next: We use the BitArray type. This example initializes a BitArray from a bool array.

Here: The program creates a bool array with true and false values, and then the BitArray constructor converts those into one bit each.

Bool Array

Info: This means that instead of one byte for a bool, the values are stored as one bit, in one-eighth the space.

True, False
C# program that creates new BitArray using System; using System.Collections; class Program { static void Main() { // Create array of 5 elements and 3 true values. bool[] array = new bool[5]; array[0] = true; array[1] = false; // <-- False value is default array[2] = true; array[3] = false; array[4] = true; // Create BitArray from the array. BitArray bitArray = new BitArray(array); // Display all bits. foreach (bool bit in bitArray) { Console.WriteLine(bit); } } } Output True False True False True
Set, count. Here we assign bits with the indexer and the Set method, and also Count the BitArray's capacity. The program here also shows how to count bits set to one in a loop. This loop is likely far slower than more optimized bitcounting methods.Bitcounts

Count: The Count on BitArray instances does not return the number of set bits. Instead, it returns the count of all bits of any value.

Therefore: You will need to loop over bits individually to count them. You can also use a for-loop.

C# program that sets and counts bits using System; using System.Collections; class Program { static void Main() { // Create BitArray from the array. BitArray bitArray = new BitArray(32); // Set three bits to 1. bitArray[3] = true; // You can set the bits with the indexer. bitArray[5] = true; bitArray.Set(10, true); // You can set the bits with Set. // Count returns the total of all bits (1s and 0s). Console.WriteLine("--- Total bits ---"); Console.WriteLine(bitArray.Count); // You can loop to count set bits. Console.WriteLine("--- Total bits set to 1 ---"); Console.WriteLine(CountBitArray(bitArray)); } /// <summary> /// Count set bits in BitArray. /// </summary> static int CountBitArray(BitArray bitArray) { int count = 0; foreach (bool bit in bitArray) { if (bit) { count++; } } return count; } } Output --- Total bits --- 32 --- Total bits set to 1 --- 3
Display. Here we display all the bits as ones and zeros in a BitArray. This is easier than doing the iteration with bitwise operators. We also use the bitwise And method on BitArray, which shows how to get all the bits that are one in both arrays.
C# program that displays bits and uses And using System; using System.Collections; class Program { static void Main() { // // Initialize BitArray with 4 true bits and 12 false bits. // BitArray bitArray1 = new BitArray(16); bitArray1.Set(0, true); bitArray1.Set(1, true); bitArray1.Set(4, true); bitArray1.Set(5, true); // // Display the BitArray. // DisplayBitArray(bitArray1); // // Initialize BitArray with two set bits. // BitArray bitArray2 = new BitArray(16); bitArray2.Set(0, true); bitArray2.Set(7, true); DisplayBitArray(bitArray2); // // And the bits. // bitArray1.And(bitArray2); DisplayBitArray(bitArray1); } /// <summary> /// Display bits as 0s and 1s. /// </summary> static void DisplayBitArray(BitArray bitArray) { for (int i = 0; i < bitArray.Count; i++) { bool bit = bitArray.Get(i); Console.Write(bit ? 1 : 0); } Console.WriteLine(); } } Output 1100110000000000 1000000100000000 1000000000000000
Bitwise methods. The BitArray class defines several more useful methods you can call. These methods, including the bitwise operations Not(), Or() and Xor() provide functionality equivalent to the bitwise operators.

Note: You can find more reference on the behavior of these operators on Wikipedia.

Internals. BitArray contains an integer array that stores the bits themselves, and a separate length value. The length member is accessed through the Count property. The Get method returns bit values by using an "AND" and shift on the internal array.
Internal members of BitArray: private int[] m_array; private int m_length;
Internally, each call to Get will result in the method checking all the parameters. This introduces two extra branches, which may be a burden on certain algorithms that require top performance.

Therefore: The BitArray is unsuitable for performance-sensitive applications that access many separate bits.

Memory allocation. I instrumented an application with CLRProfiler, which revealed that each bit in a BitArray is stored as a single bit in memory. Therefore, BitArray uses eight times less memory on large bit collections.
A summary. BitArray is a powerful wrapper over the complex bitwise operations that connect an array of four-byte integers with single bits. It is memory-efficient and easy to reuse.
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