Copy StringDictionary to Array at the specified index in C#

The StringDictionary class in C# provides the CopyTo() method to copy its key-value pairs to a DictionaryEntry array starting at a specified index. This method is useful when you need to convert dictionary data into an array format for processing or manipulation.

Syntax

The syntax for copying a StringDictionary to an array at a specified index is −

stringDictionary.CopyTo(array, index);

Parameters

• array − The destination DictionaryEntry[] array where elements will be copied.
• index − The zero-based index in the array where copying begins.

Using CopyTo() Starting at Index 0

This example demonstrates copying all StringDictionary entries to an array starting from index 0 −

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

public class Demo {
   public static void Main(){
      StringDictionary strDict = new StringDictionary();
      strDict.Add("1", "SUV");
      strDict.Add("2", "AUV");
      strDict.Add("3", "Electric Car");
      strDict.Add("4", "Utility Vehicle");
      strDict.Add("5", "Hatchback");
      strDict.Add("6", "Compact car");
      strDict.Add("7", "MUV");
      strDict.Add("8", "Crossover");
      strDict.Add("9", "Convertible");
      strDict.Add("10", "Quadricycle");
      
      DictionaryEntry[] arr = new DictionaryEntry[strDict.Count];
      strDict.CopyTo(arr, 0);
      
      Console.WriteLine("StringDictionary copied to array:");
      for (int i = 0; i < arr.Length; i++) {
         Console.WriteLine(arr[i].Key + " " + arr[i].Value);
      }
   }
}

The output of the above code is −

StringDictionary copied to array:
10 Quadricycle
1 SUV
2 AUV
3 Electric Car
4 Utility Vehicle
5 Hatchback
6 Compact car
7 MUV
8 Crossover
9 Convertible

Using CopyTo() Starting at Specified Index

This example shows copying StringDictionary entries to an array starting from index 2, leaving the first two positions empty −

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

public class Demo {
   public static void Main(){
      StringDictionary strDict = new StringDictionary();
      strDict.Add("1", "SUV");
      strDict.Add("2", "AUV");
      strDict.Add("3", "Electric Car");
      strDict.Add("4", "Utility Vehicle");
      strDict.Add("5", "Hatchback");
      strDict.Add("6", "Compact car");
      
      DictionaryEntry[] arr = new DictionaryEntry[strDict.Count + 2];
      strDict.CopyTo(arr, 2);
      
      Console.WriteLine("Array contents after copying at index 2:");
      for (int i = 0; i < arr.Length; i++) {
         if (arr[i].Key != null)
            Console.WriteLine("Index " + i + ": " + arr[i].Key + " " + arr[i].Value);
         else
            Console.WriteLine("Index " + i + ": Empty");
      }
   }
}

The output of the above code is −

Array contents after copying at index 2:
Index 0: Empty
Index 1: Empty
Index 2: 1 SUV
Index 3: 2 AUV
Index 4: 3 Electric Car
Index 5: 4 Utility Vehicle
Index 6: 5 Hatchback
Index 7: 6 Compact car

Key Points

• The destination array must be of type DictionaryEntry[] to hold both keys and values.
• The array must have enough space from the specified index to accommodate all dictionary entries.
• StringDictionary stores keys in lowercase, so the order may differ from insertion order.
• If the array is too small, an ArgumentException will be thrown.

Conclusion

The CopyTo() method of StringDictionary provides an efficient way to transfer dictionary contents to a DictionaryEntry array at any specified starting index. This is particularly useful for data processing scenarios where array operations are preferred over dictionary operations.