How to create a StringDictionary in C#?

The StringDictionary in C# is a specialized collection class from the System.Collections.Specialized namespace that stores key-value pairs where both keys and values are strings. It's important to note that StringDictionary is case-insensitive and automatically converts all keys to lowercase.

Note: StringDictionary is considered legacy and is generally replaced by Dictionary<string, string> in modern C# applications. However, understanding StringDictionary is useful for maintaining older codebases.

Syntax

Following is the syntax for creating and using a StringDictionary −

StringDictionary stringDict = new StringDictionary();
stringDict.Add("key", "value");
string value = stringDict["key"];

Creating a Basic StringDictionary

Example

using System;
using System.Collections;
using System.Collections.Specialized;

public class Demo {
   public static void Main() {
      StringDictionary strDict = new StringDictionary();
      strDict.Add("A", "John");
      strDict.Add("B", "Andy");
      strDict.Add("C", "Tim");
      strDict.Add("D", "Ryan");
      strDict.Add("E", "Kevin");
      strDict.Add("F", "Katie");
      strDict.Add("G", "Brad");
      
      Console.WriteLine("StringDictionary elements...");
      foreach(DictionaryEntry de in strDict) {
         Console.WriteLine(de.Key + " " + de.Value);
      }
   }
}

The output of the above code is −

StringDictionary elements...
a John
b Andy
c Tim
d Ryan
e Kevin
f Katie
g Brad

Accessing Values by Key

Example

using System;
using System.Collections.Specialized;

public class Demo {
   public static void Main() {
      StringDictionary myDict = new StringDictionary();
      myDict.Add("1", "Tablet");
      myDict.Add("2", "Desktop");
      myDict.Add("3", "Speakers");
      myDict.Add("4", "Laptop");
      myDict.Add("5", "Notebook");
      myDict.Add("6", "Ultrabook");
      myDict.Add("7", "HDD");
      myDict.Add("8", "SSD");
      myDict.Add("9", "Headphone");
      myDict.Add("10", "Earphone");
      
      Console.WriteLine("Value for key 5 = " + myDict["5"]);
      Console.WriteLine("Total items: " + myDict.Count);
   }
}

The output of the above code is −

Value for key 5 = Notebook
Total items: 10

Common Operations

Example

using System;
using System.Collections.Specialized;

public class Demo {
   public static void Main() {
      StringDictionary dict = new StringDictionary();
      
      // Adding items
      dict.Add("Name", "Alice");
      dict.Add("AGE", "25");  // Key will be stored as "age"
      dict.Add("city", "New York");
      
      // Accessing with different case - all work the same
      Console.WriteLine("Name: " + dict["name"]);        // Works
      Console.WriteLine("Age: " + dict["AGE"]);          // Works
      Console.WriteLine("City: " + dict["CITY"]);        // Works
      
      // Check if key exists
      Console.WriteLine("Contains 'NAME': " + dict.ContainsKey("NAME"));
      
      // Remove an item
      dict.Remove("age");
      Console.WriteLine("Count after removal: " + dict.Count);
   }
}

The output of the above code is −

Name: Alice
Age: 25
City: New York
Contains 'NAME': True
Count after removal: 2

StringDictionary vs Dictionary<string, string>

Conclusion

StringDictionary in C# provides a case-insensitive way to store string key-value pairs, automatically converting all keys to lowercase. While functional, modern C# applications should prefer Dictionary<string, string> for better performance and type safety, using StringComparer.OrdinalIgnoreCase when case-insensitive behavior is needed.