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C# StringDictionary Class - GeeksforGeeks

C# StringDictionary Class

Last Updated : 11 Jul, 2025

In C#, the StringDictionary class is the part of the System.Collections.Specialized namespace. It is a collection of key-value pairs where the keys are strings and values are objects. It is similar to a Hashtable. But it is specifically designed for use with string keys.

Keys are always strings, and values can be any object.
It does not maintain the order of insertion of elements.
Provides indexed access to values based on string keys.
By default, it is case-sensitive.

Example: This example demonstrates how to use the StringDictionary class to store and iterate over key-value pairs where keys are strings and values can be any object.


 // C# program to demonstrate StringDictionary class
using System;
using System.Collections;
using System.Collections.Specialized;

class Geeks
{
    static void Main()
    {
        // Create a StringDictionary
        StringDictionary sd = new StringDictionary();

        // Insert key-value pairs
        sd.Add("1", "Geek1");
        sd.Add("2", "Geek2");
        sd.Add("3", "Geek3");
        sd.Add("4", "Geek4");

        // Iterate through the StringDictionary 
        // and print the key-value pairs
        foreach (DictionaryEntry i in sd)
        {
            Console.WriteLine($"{i.Key} --> {i.Value}");
        }
    }
}

Output

3 --> Geek3
4 --> Geek4
2 --> Geek2
1 --> Geek1

Declaration of StringDictionary

In C#, the StringDictionary is declared as:

StringDictionary dictionary = new StringDictionary();

Constructor

StringDictionary(): Initializes a new instance of the StringDictionary class.

Example: This example demonstrates how to create a StringDictionary, add integer values as string, and iterate through the dictionary to display the keys and their corresponding values.


 // C# program to demonstrates how to 
// create a StringDictionary 
using System; 
using System.Collections; 
using System.Collections.Specialized; 

class Geeks { 

	public static void Main() 
	{ 

		// Creating a StringDictionary
		StringDictionary sd = new StringDictionary(); 

		// Adding key and value into the StringDictionary 
		sd.Add("X", "100"); 
		sd.Add("Y", "200"); 
		sd.Add("Z", "300"); 

		// Displaying the keys and values in StringDictionary 
		foreach(DictionaryEntry i in sd) 
		{ 
			Console.WriteLine(i.Key + " --> " + i.Value); 
		} 
	} 
}

Output

x --> 100
z --> 300
y --> 200

Properties Properties Description Count Gets the number of key/value pairs in the StringDictionary. IsSynchronized Gets a value indicating whether access to the StringDictionary is synchronized (thread safe). Item[String] Gets or sets the value associated with the specified key. Keys Gets a collection of keys in the StringDictionary. SyncRoot Gets an object that can be used to synchronize access to the StringDictionary. Values Gets a collection of values in the StringDictionary.

Example: This example demonstrates how to use Values property to access that values in StringDictionary and check its IsSynchronized property to determine if its thread-safe.


 // C# program to demonstrates the working of 
// values and IsSynchronized property
using System;
using System.Collections;
using System.Collections.Specialized;

class Geeks{

    public static void Main() {

        // Creating a StringDictionary
        StringDictionary sd = new StringDictionary();

        // Adding key and value 
        sd.Add("1", "One");
        sd.Add("5", "Five");
        sd.Add("7", "Seven");
        sd.Add("10", "Ten");

        // Values Property

        // Getting a collection of values in the StringDictionary
        foreach (string i in sd.Values) {
            Console.WriteLine(i);
        }

        // IsSynchronized Property

        // Checking if StringDictionary is synchronized(thread-safe)
        Console.WriteLine(sd.IsSynchronized);
    }
}

Output

Five
Seven
Ten
One
False

Methods Methods Description Add(String, String) Adds an entry with the specified key and value into the StringDictionary. Clear() Removes all entries from the StringDictionary. ContainsKey(String) Determines if the StringDictionary contains a specific key. ContainsValue(String) Determines if the StringDictionary contains a specific value. CopyTo(Array, Int32) Copies the string dictionary values to a one-dimensional Array instance at the specified index. Equals(Object) Determines whether the specified object is equal to the current object. GetEnumerator() Returns an enumerator that iterates through the string dictionary. GetHashCode() Serves as the default hash function. GetType() Gets the Type of the current instance. MemberwiseClone() Creates a shallow copy of the current Object. Remove(String) Removes the entry with the specified key from the string dictionary. ToString() Returns a string that represents the current object.

Example 1: This example demonstrates how to use the Count property to get the number of key-value pairs and how to remove key-value pair using the Remove() method.


 // C# code to remove the entry 
// with the specified key from 
// the StringDictionary 
using System; 
using System.Collections; 
using System.Collections.Specialized; 

class Geeks { 

	public static void Main() 
	{ 

		// Creating a StringDictionary 
		StringDictionary sd = new StringDictionary(); 

		// Adding key and value into the StringDictionary 
		sd.Add("X", "100"); 
		sd.Add("Y", "200"); 
		sd.Add("Z", "300"); 
	
		// Displaying the keys and values in StringDictionary 
		Console.WriteLine("The number of key-value pairs are : " + sd.Count); 

		// Removing the entry with the specified 
		// key from the StringDictionary 
		sd.Remove("Y"); 

		// Displaying the keys and values in StringDictionary 
		Console.WriteLine("The number of key-value pairs are : " + sd.Count); 
	} 
}

Output

The number of key-value pairs are : 3
The number of key-value pairs are : 2

Example 2: This example demonstrates how to use the CopyTo method to copy the contents of a StringDicitonary into an array and then display the key-value pairs from the array.


 // C# code to copy StringDictionary
// to Array at the specified index
using System;
using System.Collections;
using System.Collections.Specialized;

class Geeks {

    public static void Main()
    {

        // Creating a StringDictionary
        StringDictionary sd = new StringDictionary();

        // Adding key and value into the StringDictionary
        sd.Add("1", "Geeks");
        sd.Add("2", "for");
        sd.Add("3", "Geeks");

        // Creating an Array
        DictionaryEntry[] arr = { new DictionaryEntry(),
                                  new DictionaryEntry(),
                                  new DictionaryEntry() };

        // Copying StringDictionary to
        // Array at the specified index
        sd.CopyTo(arr, 0);

        // Displaying key and value pairs in Array
        for (int i = 0; i < arr.Length; i++) {
            Console.WriteLine(arr[i].Key + " --> "
                              + arr[i].Value);
        }
    }
}

Output

3 --> Geeks
2 --> for
1 --> Geeks

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