C# | Copy StringCollection at the specified index of array

Last Updated : 01 Feb, 2019

StringCollection class is a new addition to the .NET Framework class library that represents a collection of strings. StringCollection class is defined in the System.Collections.Specialized namespace.

StringCollection.CopyTo(String[], Int32) method is used to copy the entire StringCollection values to a one-dimensional array of strings which starts at the specified index of the target array.

Syntax:

  public void CopyTo (string[] array, int index);

Parameters:

array : It is the one-dimensional array of strings that is the destination of the elements copied from StringCollection. The Array must have zero-based indexing.
index : It is the zero-based index in array at which copying begins.

Exceptions:

ArgumentNullException : If the array is null.
ArgumentOutOfRangeException : If the index is less than zero.
InvalidCastException : If the type of the source StringCollection cannot be cast automatically to the type of the destination array.
ArgumentException : If the array is multidimensional or the number of elements in the source StringCollection is greater than the available space from index to the end of the destination array.

Note:

The specified array must be of a compatible type.
This method is an O(n) operation, where n is Count.

Below given are some examples to understand the implementation in a better way:

Example 1:

   // C# code to copy StringCollection to array, 
// starting at the specified index of 
// the target array 
using System; 
using System.Collections; 
using System.Collections.Specialized; 
  
class GFG { 
  
    // Driver code 
    public static void Main() 
    { 
  
        // creating a StringCollection named myCol 
        StringCollection myCol = new StringCollection(); 
  
        // creating a string array named myArr1 
        String[] myArr1 = new String[] { "A", "B", "C", "D", "E" }; 
  
        // Copying the elements of a string 
        // array to the end of the StringCollection. 
        myCol.AddRange(myArr1); 
  
        // creating a String array named myArr2 
        String[] myArr2 = new String[myCol.Count]; 
  
        // Copying StringCollection to array myArr2 
        // starting from index 0 
        myCol.CopyTo(myArr2, 0); 
  
        // Displaying elements in array myArr2 
        for (int i = 0; i < myArr2.Length; i++) { 
            Console.WriteLine(myArr2[i]); 
        } 
    } 
} 
 
  

Output:

  A  B  C  D  E

Example 2:

   // C# code to copy StringCollection to array, 
// starting at the specified index of 
// the target array 
using System; 
using System.Collections; 
using System.Collections.Specialized; 
  
class GFG { 
  
    // Driver code 
    public static void Main() 
    { 
  
        // creating a StringCollection named myCol 
        StringCollection myCol = new StringCollection(); 
  
        // creating a string array named myArr1 
        String[] myArr1 = new String[] {"1", "2", "3", 
                                       "4", "5", "6"}; 
  
        // Copying the elements of a string 
        // array to the end of the StringCollection. 
        myCol.AddRange(myArr1); 
  
        // creating a String array named myArr2 
        String[] myArr2 = new String[myCol.Count]; 
  
        // Copying StringCollection to array myArr2 
        // starting from index -1 
        // This should raise exception "ArgumentOutOfRangeException" 
        // as index is less than 0 
        myCol.CopyTo(myArr2, -1); 
  
        // Displaying elements in array myArr2 
        for (int i = 0; i < myArr2.Length; i++) { 
            Console.WriteLine(myArr2[i]); 
        } 
    } 
} 
 
  

Output:

Unhandled Exception:
System.ArgumentOutOfRangeException: Value has to be >= 0.
Parameter name: destinationIndex

Reference:

https://docs.microsoft.com/en-us/dotnet/api/system.collections.specialized.stringcollection.copyto?view=netframework-4.7.2

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