Bitarray VS bool[]

Question

I expected to find a existing question here on SO about this but i didn't.

What is the advantage of using a Bitarray when you can store your bool values in a bool[]?

System.Collections.BitArray biArray = new System.Collections.BitArray(8);
biArray[4] = true;

bool[] boArray = new bool[8];
boArray[4] = true;

The bool[] seems a little more handy to me because there exist more (extension)methods to work with a array instead of a BitArray

Answer 1

There's a memory/performance tradeoff. BitArray will store 8 entries per byte, but accessing a single entry requires a bunch of logical operations under the hood. A bool array will store each entry as one byte and thus taking up more memory, but requiring fewer CPU cycles to access.

Essentially, BitArray is a memory optimization over bool[], but there's no point in using it unless memory is sparse.

Edit: Created a simple performance test. Inversing 500M elements using BitArray takes 6 seconds on my machine:

const int limit = 500000000;
var bitarray = new BitArray(limit);
for (var i = 0; i < limit; ++i)
{
    bitarray[i] = !bitarray[i];
}

The same test using a bool array takes about 1.5 seconds:

const int limit = 500000000;
var boolarray = new bool[limit];
for (var i = 0; i < limit; ++i)
{
    boolarray[i] = !boolarray[i];
}

Answer 2

BitArray is compact and allows you to perform bitwise operations. From the MSDN forum :

A BitArray uses one bit for each value, while a bool[] uses one byte for each value. You can pass to the BitArray constructor either an array of bools, an array of bytes or an array of integers. You can also pass an integer value specifying the desired length and (optionally) a boolean argument that specifies if the individual bits should be set or not.