String List

In C# we sometimes need to store strings. We might want to store some of them in a collection, packed together—in a string List.

With a string List, each element is added with a method like Add. The strings are stored separately, with references pointing to each one, in the List.

First example

Consider this example program. We create a string List and add 3 values to it—these are stored in the order added.

using System;
using System.Collections.Generic;

List<string> values = new List<string>();
values.Add("one");
values.Add("two");
values.Add("THREE");

// Use for loop.
for (int i = 0; i < values.Count; i++)
{
    // Get element at this index.
    string value = values[i];
    // Display with string interpolation.
    Console.WriteLine($"Value {i}: {value}");
}

// Use foreach loop.
foreach (string value in values)
{
    if (char.IsUpper(value[0]))
    {
        Console.WriteLine($"Uppercase: {value}");
    }
}
Value 0: one
Value 1: two
Value 2: THREE
Uppercase: THREE

Benchmark

We can use a string List instead of a string Array. But this has a performance cost. Consider this benchmark—we loop over a string List, and loop over a string Array.

using System;
using System.Collections.Generic;
using System.Diagnostics;

List<string> colorsList = new List<string>();
colorsList.Add("blue");
colorsList.Add("red");
colorsList.Add("orange");
colorsList.Add("aqua");

string[] colorsArray = new string[4];
colorsArray[0] = "blue";
colorsArray[1] = "red";
colorsArray[2] = "orange";
colorsArray[3] = "aqua";

const int _max = 2000000;
int sum = 0;
var s1 = Stopwatch.StartNew();
// Version 1: use string List.
for (int i = 0; i < _max; i++)
{
    foreach (string item in colorsList)
    {
        sum += item.Length;
    }
}
s1.Stop();
var s2 = Stopwatch.StartNew();
// Version 2: use string array.
for (int i = 0; i < _max; i++)
{
    foreach (string item in colorsArray)
    {
        sum += item.Length;
    }
}
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"));
32.93 ns    foreach string List
 4.61 ns    foreach string[]

String array note

We cannot add items to an array as easily—we must manage the size ourselves. For a string list, we can just call Add() as much as needed. This makes programs simpler.

Changing a string List to a string array may have performance benefits in programs. A simple foreach-loop may perform better. In most programs, a string List is a good choice.