C# – Parse a comma-separated string from app.config

I’ll show how to parse comma-separated integer values from app.config and load them into a HashSet for efficient lookups. First, take a look at the setting (retryStatusCodes) in app.config:

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <startup> 
        <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.6.1" />
    </startup>
  <appSettings>
    <add key="retryStatusCodes" value="408,429,503"/>
  </appSettings>
</configuration>
Code language: HTML, XML (xml)

To load and parse this setting from app.config, do the following:

• Get the setting from app.config with ConfigurationManager.AppSettings.
• Split the comma-separated string, giving you an array of string values.
• Loop over the string values and parse them into integers with int.Parse().
• Add the integers to a HashSet for later use.

The following code shows how to do this:

using System.Configuration;
using System.Linq;

var csv = ConfigurationManager.AppSettings["retryStatusCodes"];

var errorCodes = csv.Split(',').Select(i => Int32.Parse(i));

var retryStatusCodes = new HashSet<int>(errorCodes);

Console.WriteLine($"We have {retryStatusCodes.Count} retry status codes");
Console.WriteLine($"Retry when status code is 404? {retryStatusCodes.Contains(404)}");
Console.WriteLine($"Retry when status code is 429? {retryStatusCodes.Contains(429)}");
Code language: C# (cs)

Note: You have to add a reference to System.Configuration in your project (see section below).

This outputs the following:

We have 3 retry status codes
Retry when status code is 404? False
Retry when status code is 429? TrueCode language: plaintext (plaintext)

This example shows how to parse comma-separated integers, but you can apply this approach to any target type.

Add a reference to System.Configuration

To use ConfigurationManager for getting values from app.config, you’ll need to add a reference to System.Configuration:

• Right-click References.
• Click Add Reference.
• In Assemblies > Framework, find System.Configuration and tick the box.
• Click OK.