How to Parse a Comma-Separated String from App.config in C#

This is a useful technique when you want to manage multiple configuration values, such as error codes or status codes, and quickly check for their presence in your application.

Let's start with a simple setting in your app.config. We'll define a key called retryStatusCodes that holds a comma-separated list of HTTP status codes.

Here's what it looks like in your 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="301,302,403"/>
    </appSettings>
</configuration>

In this example, the retryStatusCodes setting contains three HTTP status codes (301, 302, and 503), separated by commas.

To retrieve and parse this setting in C#, follow these steps:

First, Use ConfigurationManager.AppSettings to retrieve the value from app.config.

Next, Use Split(',') to break the comma-separated string into individual values, then loop through the split strings and parse them into integers using Int32.Parse().

Finally, Use a HashSet<int> to store the parsed integers. This provides fast lookups, which is especially useful when working with larger sets of values.

Here's the code that demonstrates how to parse the retryStatusCodes setting and store the values in a HashSet<int>:

using System.Configuration;
using System.Linq;

var settings = ConfigurationManager.AppSettings["retryStatusCodes"];  // Retrieve the value from app.config
// Split the CSV string, parse each value as an integer, and create a HashSet for efficient lookup
var errorCodes = settings.Split(',').Select(i => Int32.Parse(i));
var retryStatusCodes = new HashSet<int>(errorCodes);

// Output the result
Console.WriteLine($"Total status codes: {retryStatusCodes.Count}");
Console.WriteLine($"Status code is 301? {retryStatusCodes.Contains(301)}");
Console.WriteLine($"Status code is 302? {retryStatusCodes.Contains(302)}");

Output:

Total status codes: 3
Status code is 301? False
Status code is 302? True

In order to use ConfigurationManager.AppSettings to access values from app.config, you need to add a reference to System.Configuration in your project.

You can do that by right-clicking on References in the Solution Explorer, then click Add Reference.

In the Assemblies section, locate System.Configuration, and check the box next to it, then click OK.