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C# DictionaryEntry Type

DictionaryEntry is used with Hashtable. The Hashtable collection provides a way to access objects based on a key. But it does not implement advanced logic for iterating over the contents. We use DictionaryEntry in a foreach-loop.


Example. This example uses the Hashtable type and instantiates it upon the managed heap. Then, three key-value pairs are added to the instance. Third, we use the foreach-loop construct to loop over the contents of the Hashtable instance.

Hashtable

Note: This gives us a pair of values, encoded in a DictionaryEntry struct value.

Struct

Also: To access the key and value of a DictionaryEntry, please use the named properties.

C# program that uses DictionaryEntry type and foreach

using System;
using System.Collections;

class Program
{
    static void Main()
    {
	// Create hashtable with some keys and values.
	Hashtable hashtable = new Hashtable();
	hashtable.Add(1, "one");
	hashtable.Add(2, "two");
	hashtable.Add(3, "three");

	// Enumerate the hashtable.
	foreach (DictionaryEntry entry in hashtable)
	{
	    Console.WriteLine("{0} = {1}", entry.Key, entry.Value);
	}
    }
}

Output

3 = three
2 = two
1 = one


Discussion. DictionaryEntry is not tied to the Hashtable collection. You can create an instance to store a key-value pair anywhere. Because this type is a value type, it is copied onto the evaluation stack whenever used as a variable or parameter.

And: The DictionaryEntry stores two object pointers, which are four bytes on 32-bit operating systems but eight bytes on 64-bit systems.


Summary. To loop over a Hashtable collection, then, you can use a foreach-loop construct and then access the properties on each DictionaryEntry. As with many associative collections, the looping order is undefined.

Value type: The DictionaryEntry type, as a value type, does not incur the overhead of objects.

Further: It can be instantiated anywhere in your program to store a pair of object references.