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.
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.
Version 1 This foreach-loop is done of the string List. Accesses each string in the list.
Version 2 This foreach-loop acts on the string Array. It gets the length for each string (the same as Version 1).
Result The string Array is faster for the foreach-loop. Even if the tests are reordered, the result seems to be consistent.
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.
A summary. 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.
Dot Net Perls is a collection of tested code examples. Pages are continually updated to stay current, with code correctness a top priority.
Sam Allen is passionate about computer languages. In the past, his work has been recommended by Apple and Microsoft and he has studied computers at a selective university in the United States.
