C# - char Array - Dot Net Perls

Char array. A C# char array stores string data. Each character can be accessed (and changed) without copying the rest of the characters. It enables optimizations.

A char array is an alternative to using StringBuilder for quickly creating string data. We evaluate StringBuilder and compare it to character arrays.

StringBuilder

Array

Example. First we create new char arrays. When you use the new operator, the execution engine allocates memory on the managed heap.

new

Note Array elements are stored together in one block of memory. This reduces the overhead with storing separate objects.

object

And Char is a value type so the value itself, not a reference, is stored in the storage location.

char

using System; char[] array1 = { 'a', 'b', 'c' }; char[] array2 = new char[] { 'a', 'b', 'c' }; char[] array3 = new char[3]; array3[0] = 'a'; array3[1] = 'b'; array3[2] = 'c'; // Write total length. Console.WriteLine("LENGTH: {0}", array1.Length + array2.Length + array3.Length);

LENGTH: 9

Benchmark, char array. Character arrays can be used to store character data such as letters or numbers. Here we append characters one-by-one to an array using the char data type.

Note Remember that chars in the C# language are 2 bytes. So for each char, 2 bytes are copied on the stack.

Version 1 This version uses a char array. We assign each index to the char we want to append. We use the string constructor.

String Constructor

Version 2 We use StringBuilder here. With StringBuilder, you could keep appending items to the buffer after the 100th char.

Result With .NET 5 on Linux (in 2021) this benchmark still shows that using a char array is much faster than the StringBuilder.

using System; using System.Diagnostics; using System.Text; const int _max = 1000000; var s1 = Stopwatch.StartNew(); // Version 1: use a new char array. for (int i = 0; i < _max; i++) { char[] buffer = new char[100]; for (int v = 0; v < 100; v++) { buffer[v] = 'a'; } string result = new string(buffer); } s1.Stop(); var s2 = Stopwatch.StartNew(); // Version 2: use a StringBuilder. for (int i = 0; i < _max; i++) { StringBuilder builder = new StringBuilder(100); for (int v = 0; v < 100; v++) { builder.Append('a'); } string result = builder.ToString(); } s2.Stop(); Console.WriteLine(((double)(s1.Elapsed.TotalMilliseconds * 1000000) / _max).ToString("0.00 ns")); Console.WriteLine(((double)(s2.Elapsed.TotalMilliseconds * 1000000) / _max).ToString("0.00 ns"));

86.30 ns char array 288.69 ns StringBuilder

Notes, performance. Char arrays are faster because they have fewer features. Meanwhile StringBuilder handles many cases and has many methods.

And StringBuilder is easy to use and a great optimization, but it is far slower in simple cases. It can help in real programs.

Note We used char arrays as an improvement in the alphanumeric sorting algorithm. This improved performance.

Sort Alphanumeric

Result Char arrays can be around 7 times faster on certain tasks. Char buffers have a big performance advantage.

A discussion. Using char arrays allows us to use more lower-level algorithms with greater performance. The char array code forces us to have more "coding discipline."

And It is more exact if you can enforce the constraints of char arrays (like the fixed length).

Array Length

Note StringBuilder could have extra chars appended, but the char array wouldn't allow that.

Detail The IndexOutOfRangeException that would be thrown is useful for debugging the algorithm.

IndexOutOfRangeException

Summary. Using char arrays is better when you know in advance the number of characters. StringBuilder is fast and useful, but using char arrays is sometimes more appropriate.