C# - char Combine: Get String From chars

Char combine. In C# several chars can be concatenated or combined into a string. We test whether the string.Concat method is useful.

Method info. We look at a way you can combine several characters. And we consider the fastest and most elegant ways of merging characters together.

string.Concat

Example. Here we see a method that deals with char arrays and the new string constructor. When you need to build a string char-by-char, you should use a char array for best performance.

char Array

Start We call the CharCombine method by passing it 4 chars. We can adapt the code to be used on any number of chars.

Info CharCombine allocates a new char array with 4 elements. Then, it assigns slots at indices 0 to 3 to the four parameter chars.

Finally The new string constructor is invoked in the return statement, which builds the string from the char buffer we created.

String Constructor

return

using System;

class Program
{
    public static string CharCombine(char c0, char c1, char c2, char c3)
    {
        // Allocate an array, and assign its elements to the arguments, then convert to a string.
        char[] array = new char[4];
        array[0] = c0;
        array[1] = c1;
        array[2] = c2;
        array[3] = c3;
        return new string(array);
    }

    static void Main()
    {
        char a = 'a';
        char b = 'b';
        char c = 'c';
        char d = 'd';
        char e = 'e';
        // Use CharCombine method.
        Console.WriteLine(CharCombine(a, b, c, d));
        Console.WriteLine(CharCombine(b, c, d, e));
    }
}abcd
bcde

Benchmark. What is the fastest way to convert multiple chars to a string? This benchmark will help us learn the answer to this question. The CharCombine() method is faster.

Version 1 Here we call CharCombine() with 4 arguments in a tight loop. We ensure the returned strings are valid.

Version 2 The alternative here is the string.Concat method, which you can use with "+" between the chars with ToString().

Result In .NET 8, using a char array to combine multiple chars into a string is significantly faster.

using System;
using System.Diagnostics;

class Program
{
    public static string CharCombine(char c0, char c1, char c2, char c3)
    {
        char[] array = new char[4];
        array[0] = c0;
        array[1] = c1;
        array[2] = c2;
        array[3] = c3;
        return new string(array);
    }

    public static void Main()
    {
        char a = 'a';
        char b = 'b';
        char c = 'c';
        char d = 'd';

        const int _max = 1000000;
        var s1 = Stopwatch.StartNew();
        // Version 1: combine chars with char array.
        for (int i = 0; i < _max; i++)
        {
            string v1 = CharCombine(a, b, c, d);
            string v2 = CharCombine(d, c, b, a);
            if (v1 != "abcd" || v2 != "dcba") {
                return;
            }
        }
        s1.Stop();
        var s2 = Stopwatch.StartNew();
        // Version 2: use ToString and concatenation.
        for (int i = 0; i < _max; i++)
        {
            string v1 = a.ToString() + b.ToString() + c.ToString() + d.ToString();
            string v2 = d.ToString() + c.ToString() + b.ToString() + a.ToString();
            if (v1 != "abcd" || v2 != "dcba") {
                return;
            }
        }
        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"));
    }
}22.27 ns    CharCombine
60.78 ns    +

Summary. We allocated a char array as a buffer to store 4 chars. You can easily adapt the method to handle two, three, five, or even more chars, and it will likely perform well.