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.

Example

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

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.

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.

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."

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.