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C# String List ExampleUse a string List with the generic type syntax. Loop over a string List.
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.
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.
Enum
For We use a for-loop over the string List. See carefully how the index is used to access each item in the values List.
For
Foreach The foreach-loop passes over all elements, and no index int is used. We test each string with char.IsUpper.
Foreach
C# program that uses string List
using System; using System.Collections.Generic; class Program { static void Main() { 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.
C# program that benchmarks string List
using System; using System.Collections.Generic; using System.Diagnostics; class Program { static void Main() { 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.
Array
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.
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